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GNU Coreutils
*************

This manual documents version 8.4 of the GNU core utilities, including
the standard programs for text and file manipulation.

   Copyright (C) 1994-1996, 2000-2010 Free Software Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.3 or any later version published by the Free Software
     Foundation; with no Invariant Sections, with no Front-Cover Texts,
     and with no Back-Cover Texts.  A copy of the license is included
     in the section entitled "GNU Free Documentation License".

* Menu:

* Introduction::                 Caveats, overview, and authors
* Common options::               Common options
* Output of entire files::       cat tac nl od base64
* Formatting file contents::     fmt pr fold
* Output of parts of files::     head tail split csplit
* Summarizing files::            wc sum cksum md5sum sha1sum sha2
* Operating on sorted files::    sort shuf uniq comm ptx tsort
* Operating on fields::          cut paste join
* Operating on characters::      tr expand unexpand
* Directory listing::            ls dir vdir dircolors
* Basic operations::             cp dd install mv rm shred
* Special file types::         mkdir rmdir unlink mkfifo mknod ln link readlink
* Changing file attributes::     chgrp chmod chown touch
* Disk usage::                   df du stat sync truncate
* Printing text::                echo printf yes
* Conditions::                   false true test expr
* Redirection::                  tee
* File name manipulation::       dirname basename pathchk mktemp
* Working context::              pwd stty printenv tty
* User information::             id logname whoami groups users who
* System context::               date arch uname hostname hostid uptime
* SELinux context::              chcon runcon
* Modified command invocation::  chroot env nice nohup stdbuf su timeout
* Process control::              kill
* Delaying::                     sleep
* Numeric operations::           factor seq
* File permissions::             Access modes
* Date input formats::           Specifying date strings
* Opening the software toolbox:: The software tools philosophy
* GNU Free Documentation License:: Copying and sharing this manual
* Concept index::                General index

 --- The Detailed Node Listing ---

Common Options

* Exit status::                  Indicating program success or failure
* Backup options::               Backup options
* Block size::                   Block size
* Signal specifications::        Specifying signals
* Disambiguating names and IDs:: chgrp and chown owner and group syntax
* Random sources::               Sources of random data
* Target directory::             Target directory
* Trailing slashes::             Trailing slashes
* Traversing symlinks::          Traversing symlinks to directories
* Treating / specially::         Treating / specially
* Standards conformance::        Standards conformance

Output of entire files

* cat invocation::               Concatenate and write files
* tac invocation::               Concatenate and write files in reverse
* nl invocation::                Number lines and write files
* od invocation::                Write files in octal or other formats
* base64 invocation::            Transform data into printable data

Formatting file contents

* fmt invocation::               Reformat paragraph text
* pr invocation::                Paginate or columnate files for printing
* fold invocation::              Wrap input lines to fit in specified width

Output of parts of files

* head invocation::              Output the first part of files
* tail invocation::              Output the last part of files
* split invocation::             Split a file into fixed-size pieces
* csplit invocation::            Split a file into context-determined pieces

Summarizing files

* wc invocation::                Print newline, word, and byte counts
* sum invocation::               Print checksum and block counts
* cksum invocation::             Print CRC checksum and byte counts
* md5sum invocation::            Print or check MD5 digests
* sha1sum invocation::           Print or check SHA-1 digests
* sha2 utilities::               Print or check SHA-2 digests

Operating on sorted files

* sort invocation::              Sort text files
* shuf invocation::              Shuffle text files
* uniq invocation::              Uniquify files
* comm invocation::              Compare two sorted files line by line
* ptx invocation::               Produce a permuted index of file contents
* tsort invocation::             Topological sort

`ptx': Produce permuted indexes

* General options in ptx::       Options which affect general program behavior
* Charset selection in ptx::     Underlying character set considerations
* Input processing in ptx::      Input fields, contexts, and keyword selection
* Output formatting in ptx::     Types of output format, and sizing the fields
* Compatibility in ptx::         The GNU extensions to `ptx'

Operating on fields

* cut invocation::               Print selected parts of lines
* paste invocation::             Merge lines of files
* join invocation::              Join lines on a common field

Operating on characters

* tr invocation::                Translate, squeeze, and/or delete characters
* expand invocation::            Convert tabs to spaces
* unexpand invocation::          Convert spaces to tabs

`tr': Translate, squeeze, and/or delete characters

* Character sets::               Specifying sets of characters
* Translating::                  Changing one set of characters to another
* Squeezing::                    Squeezing repeats and deleting

Directory listing

* ls invocation::                List directory contents
* dir invocation::               Briefly list directory contents
* vdir invocation::              Verbosely list directory contents
* dircolors invocation::         Color setup for `ls'

`ls':  List directory contents

* Which files are listed::       Which files are listed
* What information is listed::   What information is listed
* Sorting the output::           Sorting the output
* Details about version sort::   More details about version sort
* General output formatting::    General output formatting
* Formatting the file names::    Formatting the file names

Basic operations

* cp invocation::                Copy files and directories
* dd invocation::                Convert and copy a file
* install invocation::           Copy files and set attributes
* mv invocation::                Move (rename) files
* rm invocation::                Remove files or directories
* shred invocation::             Remove files more securely

Special file types

* link invocation::              Make a hard link via the link syscall
* ln invocation::                Make links between files
* mkdir invocation::             Make directories
* mkfifo invocation::            Make FIFOs (named pipes)
* mknod invocation::             Make block or character special files
* readlink invocation::          Print value of a symlink or canonical file name
* rmdir invocation::             Remove empty directories
* unlink invocation::            Remove files via unlink syscall

Changing file attributes

* chown invocation::             Change file owner and group
* chgrp invocation::             Change group ownership
* chmod invocation::             Change access permissions
* touch invocation::             Change file timestamps

Disk usage

* df invocation::                Report file system disk space usage
* du invocation::                Estimate file space usage
* stat invocation::              Report file or file system status
* sync invocation::              Synchronize data on disk with memory
* truncate invocation::          Shrink or extend the size of a file

Printing text

* echo invocation::              Print a line of text
* printf invocation::            Format and print data
* yes invocation::               Print a string until interrupted

Conditions

* false invocation::             Do nothing, unsuccessfully
* true invocation::              Do nothing, successfully
* test invocation::              Check file types and compare values
* expr invocation::              Evaluate expressions

`test': Check file types and compare values

* File type tests::              File type tests
* Access permission tests::      Access permission tests
* File characteristic tests::    File characteristic tests
* String tests::                 String tests
* Numeric tests::                Numeric tests

`expr': Evaluate expression

* String expressions::           + : match substr index length
* Numeric expressions::          + - * / %
* Relations for expr::           | & < <= = == != >= >
* Examples of expr::             Examples of using `expr'

Redirection

* tee invocation::               Redirect output to multiple files or processes

File name manipulation

* basename invocation::          Strip directory and suffix from a file name
* dirname invocation::           Strip non-directory suffix from a file name
* pathchk invocation::           Check file name validity and portability
* mktemp invocation::            Create temporary file or directory

Working context

* pwd invocation::               Print working directory
* stty invocation::              Print or change terminal characteristics
* printenv invocation::          Print all or some environment variables
* tty invocation::               Print file name of terminal on standard input

`stty': Print or change terminal characteristics

* Control::                      Control settings
* Input::                        Input settings
* Output::                       Output settings
* Local::                        Local settings
* Combination::                  Combination settings
* Characters::                   Special characters
* Special::                      Special settings

User information

* id invocation::                Print user identity
* logname invocation::           Print current login name
* whoami invocation::            Print effective user ID
* groups invocation::            Print group names a user is in
* users invocation::             Print login names of users currently logged in
* who invocation::               Print who is currently logged in

System context

* arch invocation::              Print machine hardware name
* date invocation::              Print or set system date and time
* nproc invocation::             Print the number of processors
* uname invocation::             Print system information
* hostname invocation::          Print or set system name
* hostid invocation::            Print numeric host identifier
* uptime invocation::            Print system uptime and load

`date': Print or set system date and time

* Time conversion specifiers::   %[HIklMNpPrRsSTXzZ]
* Date conversion specifiers::   %[aAbBcCdDeFgGhjmuUVwWxyY]
* Literal conversion specifiers:: %[%nt]
* Padding and other flags::      Pad with zeros, spaces, etc.
* Setting the time::             Changing the system clock
* Options for date::             Instead of the current time
* Date input formats::           Specifying date strings
* Examples of date::             Examples

SELinux context

* chcon invocation::             Change SELinux context of file
* runcon invocation::            Run a command in specified SELinux context

Modified command invocation

* chroot invocation::            Run a command with a different root directory
* env invocation::               Run a command in a modified environment
* nice invocation::              Run a command with modified niceness
* nohup invocation::             Run a command immune to hangups
* stdbuf invocation::            Run a command with modified I/O buffering
* su invocation::                Run a command with substitute user and group ID
* timeout invocation::           Run a command with a time limit

Process control

* kill invocation::              Sending a signal to processes.

Delaying

* sleep invocation::             Delay for a specified time

Numeric operations

* factor invocation::            Print prime factors
* seq invocation::               Print numeric sequences

File permissions

* Mode Structure::               Structure of file mode bits
* Symbolic Modes::               Mnemonic representation of file mode bits
* Numeric Modes::                File mode bits as octal numbers
* Directory Setuid and Setgid::  Set-user-ID and set-group-ID on directories

Date input formats

* General date syntax::          Common rules
* Calendar date items::          19 Dec 1994
* Time of day items::            9:20pm
* Time zone items::              EST, PDT, GMT
* Day of week items::            Monday and others
* Relative items in date strings:: next tuesday, 2 years ago
* Pure numbers in date strings:: 19931219, 1440
* Seconds since the Epoch::      @1078100502
* Specifying time zone rules::   TZ="America/New_York", TZ="UTC0"
* Authors of get_date::          Bellovin, Eggert, Salz, Berets, et al

Opening the software toolbox

* Toolbox introduction::         Toolbox introduction
* I/O redirection::              I/O redirection
* The who command::              The `who' command
* The cut command::              The `cut' command
* The sort command::             The `sort' command
* The uniq command::             The `uniq' command
* Putting the tools together::   Putting the tools together

Copying This Manual

* GNU Free Documentation License::     Copying and sharing this manual

File: coreutils.info,  Node: Introduction,  Next: Common options,  Prev: Top,  Up: Top

1 Introduction
**************

This manual is a work in progress: many sections make no attempt to
explain basic concepts in a way suitable for novices.  Thus, if you are
interested, please get involved in improving this manual.  The entire
GNU community will benefit.

   The GNU utilities documented here are mostly compatible with the
POSIX standard.  Please report bugs to <bug-coreutils AT gnu.org>.
Remember to include the version number, machine architecture, input
files, and any other information needed to reproduce the bug: your
input, what you expected, what you got, and why it is wrong.  Diffs are
welcome, but please include a description of the problem as well, since
this is sometimes difficult to infer.  *Note Bugs: (gcc)Bugs.

   This manual was originally derived from the Unix man pages in the
distributions, which were written by David MacKenzie and updated by Jim
Meyering.  What you are reading now is the authoritative documentation
for these utilities; the man pages are no longer being maintained.  The
original `fmt' man page was written by Ross Paterson.  Franc,ois Pinard
did the initial conversion to Texinfo format.  Karl Berry did the
indexing, some reorganization, and editing of the results.  Brian
Youmans of the Free Software Foundation office staff combined the
manuals for textutils, fileutils, and sh-utils to produce the present
omnibus manual.  Richard Stallman contributed his usual invaluable
insights to the overall process.

File: coreutils.info,  Node: Common options,  Next: Output of entire files,  Prev: Introduction,  Up: Top

2 Common options
****************

Certain options are available in all of these programs.  Rather than
writing identical descriptions for each of the programs, they are
described here.  (In fact, every GNU program accepts (or should accept)
these options.)

   Normally options and operands can appear in any order, and programs
act as if all the options appear before any operands.  For example,
`sort -r passwd -t :' acts like `sort -r -t : passwd', since `:' is an
option-argument of `-t'.  However, if the `POSIXLY_CORRECT' environment
variable is set, options must appear before operands, unless otherwise
specified for a particular command.

   A few programs can usefully have trailing operands with leading `-'.
With such a program, options must precede operands even if
`POSIXLY_CORRECT' is not set, and this fact is noted in the program
description.  For example, the `env' command's options must appear
before its operands, since in some cases the operands specify a command
that itself contains options.

   Most programs that accept long options recognize unambiguous
abbreviations of those options.  For example, `rmdir
--ignore-fail-on-non-empty' can be invoked as `rmdir --ignore-fail' or
even `rmdir --i'.  Ambiguous options, such as `ls --h', are identified
as such.

   Some of these programs recognize the `--help' and `--version'
options only when one of them is the sole command line argument.  For
these programs, abbreviations of the long options are not always
recognized.

`--help'
     Print a usage message listing all available options, then exit
     successfully.

`--version'
     Print the version number, then exit successfully.

`--'
     Delimit the option list.  Later arguments, if any, are treated as
     operands even if they begin with `-'.  For example, `sort -- -r'
     reads from the file named `-r'.


   A single `-' operand is not really an option, though it looks like
one.  It stands for standard input, or for standard output if that is
clear from the context.  For example, `sort -' reads from standard
input, and is equivalent to plain `sort', and `tee -' writes an extra
copy of its input to standard output.  Unless otherwise specified, `-'
can appear as any operand that requires a file name.

* Menu:

* Exit status::                 Indicating program success or failure.
* Backup options::              -b -S, in some programs.
* Block size::                  BLOCK_SIZE and --block-size, in some programs.
* Signal specifications::       Specifying signals using the --signal option.
* Disambiguating names and IDs:: chgrp and chown owner and group syntax
* Random sources::              --random-source, in some programs.
* Target directory::            Specifying a target directory, in some programs.
* Trailing slashes::            --strip-trailing-slashes, in some programs.
* Traversing symlinks::         -H, -L, or -P, in some programs.
* Treating / specially::        --preserve-root and --no-preserve-root.
* Special built-in utilities::  `break', `:', `eval', ...
* Standards conformance::       Conformance to the POSIX standard.

File: coreutils.info,  Node: Exit status,  Next: Backup options,  Up: Common options

2.1 Exit status
===============

Nearly every command invocation yields an integral "exit status" that
can be used to change how other commands work.  For the vast majority
of commands, an exit status of zero indicates success.  Failure is
indicated by a nonzero value--typically `1', though it may differ on
unusual platforms as POSIX requires only that it be nonzero.

   However, some of the programs documented here do produce other exit
status values and a few associate different meanings with the values
`0' and `1'.  Here are some of the exceptions: `chroot', `env', `expr',
`nice', `nohup', `printenv', `sort', `stdbuf', `su', `test', `timeout',
`tty'.

File: coreutils.info,  Node: Backup options,  Next: Block size,  Prev: Exit status,  Up: Common options

2.2 Backup options
==================

Some GNU programs (at least `cp', `install', `ln', and `mv') optionally
make backups of files before writing new versions.  These options
control the details of these backups.  The options are also briefly
mentioned in the descriptions of the particular programs.

`-b'
`--backup[=METHOD]'
     Make a backup of each file that would otherwise be overwritten or
     removed.  Without this option, the original versions are destroyed.
     Use METHOD to determine the type of backups to make.  When this
     option is used but METHOD is not specified, then the value of the
     `VERSION_CONTROL' environment variable is used.  And if
     `VERSION_CONTROL' is not set, the default backup type is
     `existing'.

     Note that the short form of this option, `-b' does not accept any
     argument.  Using `-b' is equivalent to using `--backup=existing'.

     This option corresponds to the Emacs variable `version-control';
     the values for METHOD are the same as those used in Emacs.  This
     option also accepts more descriptive names.  The valid METHODs are
     (unique abbreviations are accepted):

    `none'
    `off'
          Never make backups.

    `numbered'
    `t'
          Always make numbered backups.

    `existing'
    `nil'
          Make numbered backups of files that already have them, simple
          backups of the others.

    `simple'
    `never'
          Always make simple backups.  Please note `never' is not to be
          confused with `none'.


`-S SUFFIX'
`--suffix=SUFFIX'
     Append SUFFIX to each backup file made with `-b'.  If this option
     is not specified, the value of the `SIMPLE_BACKUP_SUFFIX'
     environment variable is used.  And if `SIMPLE_BACKUP_SUFFIX' is not
     set, the default is `~', just as in Emacs.


File: coreutils.info,  Node: Block size,  Next: Signal specifications,  Prev: Backup options,  Up: Common options

2.3 Block size
==============

Some GNU programs (at least `df', `du', and `ls') display sizes in
"blocks".  You can adjust the block size and method of display to make
sizes easier to read.  The block size used for display is independent
of any file system block size.  Fractional block counts are rounded up
to the nearest integer.

   The default block size is chosen by examining the following
environment variables in turn; the first one that is set determines the
block size.

`DF_BLOCK_SIZE'
     This specifies the default block size for the `df' command.
     Similarly, `DU_BLOCK_SIZE' specifies the default for `du' and
     `LS_BLOCK_SIZE' for `ls'.

`BLOCK_SIZE'
     This specifies the default block size for all three commands, if
     the above command-specific environment variables are not set.

`BLOCKSIZE'
     This specifies the default block size for all values that are
     normally printed as blocks, if neither `BLOCK_SIZE' nor the above
     command-specific environment variables are set.  Unlike the other
     environment variables, `BLOCKSIZE' does not affect values that are
     normally printed as byte counts, e.g., the file sizes contained in
     `ls -l' output.

`POSIXLY_CORRECT'
     If neither `COMMAND_BLOCK_SIZE', nor `BLOCK_SIZE', nor `BLOCKSIZE'
     is set, but this variable is set, the block size defaults to 512.


   If none of the above environment variables are set, the block size
currently defaults to 1024 bytes in most contexts, but this number may
change in the future.  For `ls' file sizes, the block size defaults to
1 byte.

   A block size specification can be a positive integer specifying the
number of bytes per block, or it can be `human-readable' or `si' to
select a human-readable format.  Integers may be followed by suffixes
that are upward compatible with the SI prefixes
(http://www.bipm.fr/enus/3_SI/si-prefixes.html) for decimal multiples
and with the IEC 60027-2 prefixes for binary multiples
(http://physics.nist.gov/cuu/Units/binary.html).

   With human-readable formats, output sizes are followed by a size
letter such as `M' for megabytes.  `BLOCK_SIZE=human-readable' uses
powers of 1024; `M' stands for 1,048,576 bytes.  `BLOCK_SIZE=si' is
similar, but uses powers of 1000 and appends `B'; `MB' stands for
1,000,000 bytes.

   A block size specification preceded by `'' causes output sizes to be
displayed with thousands separators.  The `LC_NUMERIC' locale specifies
the thousands separator and grouping.  For example, in an American
English locale, `--block-size="'1kB"' would cause a size of 1234000
bytes to be displayed as `1,234'.  In the default C locale, there is no
thousands separator so a leading `'' has no effect.

   An integer block size can be followed by a suffix to specify a
multiple of that size.  A bare size letter, or one followed by `iB',
specifies a multiple using powers of 1024.  A size letter followed by
`B' specifies powers of 1000 instead.  For example, `1M' and `1MiB' are
equivalent to `1048576', whereas `1MB' is equivalent to `1000000'.

   A plain suffix without a preceding integer acts as if `1' were
prepended, except that it causes a size indication to be appended to
the output.  For example, `--block-size="kB"' displays 3000 as `3kB'.

   The following suffixes are defined.  Large sizes like `1Y' may be
rejected by your computer due to limitations of its arithmetic.

`kB'
     kilobyte: 10^3 = 1000.

`k'
`K'
`KiB'
     kibibyte: 2^10 = 1024.  `K' is special: the SI prefix is `k' and
     the IEC 60027-2 prefix is `Ki', but tradition and POSIX use `k' to
     mean `KiB'.

`MB'
     megabyte: 10^6 = 1,000,000.

`M'
`MiB'
     mebibyte: 2^20 = 1,048,576.

`GB'
     gigabyte: 10^9 = 1,000,000,000.

`G'
`GiB'
     gibibyte: 2^30 = 1,073,741,824.

`TB'
     terabyte:  10^12 = 1,000,000,000,000.

`T'
`TiB'
     tebibyte: 2^40 = 1,099,511,627,776.

`PB'
     petabyte: 10^15 = 1,000,000,000,000,000.

`P'
`PiB'
     pebibyte: 2^50 = 1,125,899,906,842,624.

`EB'
     exabyte: 10^18 = 1,000,000,000,000,000,000.

`E'
`EiB'
     exbibyte: 2^60 = 1,152,921,504,606,846,976.

`ZB'
     zettabyte: 10^21 = 1,000,000,000,000,000,000,000

`Z'
`ZiB'
     2^70 = 1,180,591,620,717,411,303,424.  (`Zi' is a GNU extension to
     IEC 60027-2.)

`YB'
     yottabyte: 10^24 = 1,000,000,000,000,000,000,000,000.

`Y'
`YiB'
     2^80 = 1,208,925,819,614,629,174,706,176.  (`Yi' is a GNU
     extension to IEC 60027-2.)

   Block size defaults can be overridden by an explicit
`--block-size=SIZE' option.  The `-k' option is equivalent to
`--block-size=1K', which is the default unless the `POSIXLY_CORRECT'
environment variable is set.  The `-h' or `--human-readable' option is
equivalent to `--block-size=human-readable'.  The `--si' option is
equivalent to `--block-size=si'.

File: coreutils.info,  Node: Signal specifications,  Next: Disambiguating names and IDs,  Prev: Block size,  Up: Common options

2.4 Signal specifications
=========================

A SIGNAL may be a signal name like `HUP', or a signal number like `1',
or an exit status of a process terminated by the signal.  A signal name
can be given in canonical form or prefixed by `SIG'.  The case of the
letters is ignored. The following signal names and numbers are
supported on all POSIX compliant systems:

`HUP'
     1.  Hangup.

`INT'
     2.  Terminal interrupt.

`QUIT'
     3.  Terminal quit.

`ABRT'
     6.  Process abort.

`KILL'
     9.  Kill (cannot be caught or ignored).

`ALRM'
     14.  Alarm Clock.

`TERM'
     15.  Termination.

Other supported signal names have system-dependent corresponding
numbers.  All systems conforming to POSIX 1003.1-2001 also support the
following signals:

`BUS'
     Access to an undefined portion of a memory object.

`CHLD'
     Child process terminated, stopped, or continued.

`CONT'
     Continue executing, if stopped.

`FPE'
     Erroneous arithmetic operation.

`ILL'
     Illegal Instruction.

`PIPE'
     Write on a pipe with no one to read it.

`SEGV'
     Invalid memory reference.

`STOP'
     Stop executing (cannot be caught or ignored).

`TSTP'
     Terminal stop.

`TTIN'
     Background process attempting read.

`TTOU'
     Background process attempting write.

`URG'
     High bandwidth data is available at a socket.

`USR1'
     User-defined signal 1.

`USR2'
     User-defined signal 2.

POSIX 1003.1-2001 systems that support the XSI extension also support
the following signals:

`POLL'
     Pollable event.

`PROF'
     Profiling timer expired.

`SYS'
     Bad system call.

`TRAP'
     Trace/breakpoint trap.

`VTALRM'
     Virtual timer expired.

`XCPU'
     CPU time limit exceeded.

`XFSZ'
     File size limit exceeded.

POSIX 1003.1-2001 systems that support the XRT extension also support
at least eight real-time signals called `RTMIN', `RTMIN+1', ...,
`RTMAX-1', `RTMAX'.

File: coreutils.info,  Node: Disambiguating names and IDs,  Next: Random sources,  Prev: Signal specifications,  Up: Common options

2.5 chown and chgrp: Disambiguating user names and IDs
======================================================

Since the OWNER and GROUP arguments to `chown' and `chgrp' may be
specified as names or numeric IDs, there is an apparent ambiguity.
What if a user or group _name_ is a string of digits?  (1) Should the
command interpret it as a user name or as an ID?  POSIX requires that
`chown' and `chgrp' first attempt to resolve the specified string as a
name, and only once that fails, then try to interpret it as an ID.
This is troublesome when you want to specify a numeric ID, say 42, and
it must work even in a pathological situation where `42' is a user name
that maps to some other user ID, say 1000.  Simply invoking `chown 42
F', will set `F's owner ID to 1000--not what you intended.

   GNU `chown' and `chgrp' provide a way to work around this, that at
the same time may result in a significant performance improvement by
eliminating a database look-up.  Simply precede each numeric user ID
and/or group ID with a `+', in order to force its interpretation as an
integer:

     chown +42 F
     chgrp +$numeric_group_id another-file
     chown +0:+0 /

   GNU `chown' and `chgrp' skip the name look-up process for each
`+'-prefixed string, because a string containing `+' is never a valid
user or group name.  This syntax is accepted on most common Unix
systems, but not on Solaris 10.

   ---------- Footnotes ----------

   (1) Using a number as a user name is common in some environments.

File: coreutils.info,  Node: Random sources,  Next: Target directory,  Prev: Disambiguating names and IDs,  Up: Common options

2.6 Sources of random data
==========================

The `shuf', `shred', and `sort' commands sometimes need random data to
do their work.  For example, `sort -R' must choose a hash function at
random, and it needs random data to make this selection.

   By default these commands use an internal pseudorandom generator
initialized by a small amount of entropy, but can be directed to use an
external source with the `--random-source=FILE' option.  An error is
reported if FILE does not contain enough bytes.

   For example, the device file `/dev/urandom' could be used as the
source of random data.  Typically, this device gathers environmental
noise from device drivers and other sources into an entropy pool, and
uses the pool to generate random bits.  If the pool is short of data,
the device reuses the internal pool to produce more bits, using a
cryptographically secure pseudorandom number generator.  But be aware
that this device is not designed for bulk random data generation and is
relatively slow.

   `/dev/urandom' suffices for most practical uses, but applications
requiring high-value or long-term protection of private data may
require an alternate data source like `/dev/random' or `/dev/arandom'.
The set of available sources depends on your operating system.

   To reproduce the results of an earlier invocation of a command, you
can save some random data into a file and then use that file as the
random source in earlier and later invocations of the command.

File: coreutils.info,  Node: Target directory,  Next: Trailing slashes,  Prev: Random sources,  Up: Common options

2.7 Target directory
====================

The `cp', `install', `ln', and `mv' commands normally treat the last
operand specially when it is a directory or a symbolic link to a
directory.  For example, `cp source dest' is equivalent to `cp source
dest/source' if `dest' is a directory.  Sometimes this behavior is not
exactly what is wanted, so these commands support the following options
to allow more fine-grained control:

`-T'
`--no-target-directory'
     Do not treat the last operand specially when it is a directory or a
     symbolic link to a directory.  This can help avoid race conditions
     in programs that operate in a shared area.  For example, when the
     command `mv /tmp/source /tmp/dest' succeeds, there is no guarantee
     that `/tmp/source' was renamed to `/tmp/dest': it could have been
     renamed to `/tmp/dest/source' instead, if some other process
     created `/tmp/dest' as a directory.  However, if `mv -T
     /tmp/source /tmp/dest' succeeds, there is no question that
     `/tmp/source' was renamed to `/tmp/dest'.

     In the opposite situation, where you want the last operand to be
     treated as a directory and want a diagnostic otherwise, you can use
     the `--target-directory' (`-t') option.

`-t DIRECTORY'
`--target-directory=DIRECTORY'
     Use DIRECTORY as the directory component of each destination file
     name.

     The interface for most programs is that after processing options
     and a finite (possibly zero) number of fixed-position arguments,
     the remaining argument list is either expected to be empty, or is
     a list of items (usually files) that will all be handled
     identically.  The `xargs' program is designed to work well with
     this convention.

     The commands in the `mv'-family are unusual in that they take a
     variable number of arguments with a special case at the _end_
     (namely, the target directory).  This makes it nontrivial to
     perform some operations, e.g., "move all files from here to
     ../d/", because `mv * ../d/' might exhaust the argument space, and
     `ls | xargs ...' doesn't have a clean way to specify an extra
     final argument for each invocation of the subject command.  (It
     can be done by going through a shell command, but that requires
     more human labor and brain power than it should.)

     The `--target-directory' (`-t') option allows the `cp', `install',
     `ln', and `mv' programs to be used conveniently with `xargs'.  For
     example, you can move the files from the current directory to a
     sibling directory, `d' like this:

          ls | xargs mv -t ../d --

     However, this doesn't move files whose names begin with `.'.  If
     you use the GNU `find' program, you can move those files too, with
     this command:

          find . -mindepth 1 -maxdepth 1 \
            | xargs mv -t ../d

     But both of the above approaches fail if there are no files in the
     current directory, or if any file has a name containing a blank or
     some other special characters.  The following example removes
     those limitations and requires both GNU `find' and GNU `xargs':

          find . -mindepth 1 -maxdepth 1 -print0 \
            | xargs --null --no-run-if-empty \
                mv -t ../d


The `--target-directory' (`-t') and `--no-target-directory' (`-T')
options cannot be combined.

File: coreutils.info,  Node: Trailing slashes,  Next: Traversing symlinks,  Prev: Target directory,  Up: Common options

2.8 Trailing slashes
====================

Some GNU programs (at least `cp' and `mv') allow you to remove any
trailing slashes from each SOURCE argument before operating on it.  The
`--strip-trailing-slashes' option enables this behavior.

   This is useful when a SOURCE argument may have a trailing slash and
specify a symbolic link to a directory.  This scenario is in fact rather
common because some shells can automatically append a trailing slash
when performing file name completion on such symbolic links.  Without
this option, `mv', for example, (via the system's rename function) must
interpret a trailing slash as a request to dereference the symbolic link
and so must rename the indirectly referenced _directory_ and not the
symbolic link.  Although it may seem surprising that such behavior be
the default, it is required by POSIX and is consistent with other parts
of that standard.

File: coreutils.info,  Node: Traversing symlinks,  Next: Treating / specially,  Prev: Trailing slashes,  Up: Common options

2.9 Traversing symlinks
=======================

The following options modify how `chown' and `chgrp' traverse a
hierarchy when the `--recursive' (`-R') option is also specified.  If
more than one of the following options is specified, only the final one
takes effect.  These options specify whether processing a symbolic link
to a directory entails operating on just the symbolic link or on all
files in the hierarchy rooted at that directory.

   These options are independent of `--dereference' and
`--no-dereference' (`-h'), which control whether to modify a symlink or
its referent.

`-H'
     If `--recursive' (`-R') is specified and a command line argument
     is a symbolic link to a directory, traverse it.

`-L'
     In a recursive traversal, traverse every symbolic link to a
     directory that is encountered.

`-P'
     Do not traverse any symbolic links.  This is the default if none
     of `-H', `-L', or `-P' is specified.


File: coreutils.info,  Node: Treating / specially,  Next: Special built-in utilities,  Prev: Traversing symlinks,  Up: Common options

2.10 Treating `/' specially
===========================

Certain commands can operate destructively on entire hierarchies.  For
example, if a user with appropriate privileges mistakenly runs `rm -rf
/ tmp/junk', that may remove all files on the entire system.  Since
there are so few legitimate uses for such a command, GNU `rm' normally
declines to operate on any directory that resolves to `/'.  If you
really want to try to remove all the files on your system, you can use
the `--no-preserve-root' option, but the default behavior, specified by
the `--preserve-option', is safer for most purposes.

   The commands `chgrp', `chmod' and `chown' can also operate
destructively on entire hierarchies, so they too support these options.
Although, unlike `rm', they don't actually unlink files, these commands
are arguably more dangerous when operating recursively on `/', since
they often work much more quickly, and hence damage more files before
an alert user can interrupt them.  Tradition and POSIX require these
commands to operate recursively on `/', so they default to
`--no-preserve-root', but using the `--preserve-root' option makes them
safer for most purposes.  For convenience you can specify
`--preserve-root' in an alias or in a shell function.

   Note that the `--preserve-root' option also ensures that `chgrp' and
`chown' do not modify `/' even when dereferencing a symlink pointing to
`/'.

File: coreutils.info,  Node: Special built-in utilities,  Next: Standards conformance,  Prev: Treating / specially,  Up: Common options

2.11 Special built-in utilities
===============================

Some programs like `nice' can invoke other programs; for example, the
command `nice cat file' invokes the program `cat' by executing the
command `cat file'.  However, "special built-in utilities" like `exit'
cannot be invoked this way.  For example, the command `nice exit' does
not have a well-defined behavior: it may generate an error message
instead of exiting.

   Here is a list of the special built-in utilities that are
standardized by POSIX 1003.1-2004.

     . : break continue eval exec exit export readonly return set shift
     times trap unset

   For example, because `.', `:', and `exec' are special, the commands
`nice . foo.sh', `nice :', and `nice exec pwd' do not work as you might
expect.

   Many shells extend this list.  For example, Bash has several extra
special built-in utilities like `history', and `suspend', and with Bash
the command `nice suspend' generates an error message instead of
suspending.

File: coreutils.info,  Node: Standards conformance,  Prev: Special built-in utilities,  Up: Common options

2.12 Standards conformance
==========================

In a few cases, the GNU utilities' default behavior is incompatible
with the POSIX standard.  To suppress these incompatibilities, define
the `POSIXLY_CORRECT' environment variable.  Unless you are checking
for POSIX conformance, you probably do not need to define
`POSIXLY_CORRECT'.

   Newer versions of POSIX are occasionally incompatible with older
versions.  For example, older versions of POSIX required the command
`sort +1' to sort based on the second and succeeding fields in each
input line, but starting with POSIX 1003.1-2001 the same command is
required to sort the file named `+1', and you must instead use the
command `sort -k 2' to get the field-based sort.

   The GNU utilities normally conform to the version of POSIX that is
standard for your system.  To cause them to conform to a different
version of POSIX, define the `_POSIX2_VERSION' environment variable to
a value of the form YYYYMM specifying the year and month the standard
was adopted.  Two values are currently supported for `_POSIX2_VERSION':
`199209' stands for POSIX 1003.2-1992, and `200112' stands for POSIX
1003.1-2001.  For example, if you have a newer system but are running
software that assumes an older version of POSIX and uses `sort +1' or
`tail +10', you can work around any compatibility problems by setting
`_POSIX2_VERSION=199209' in your environment.

File: coreutils.info,  Node: Output of entire files,  Next: Formatting file contents,  Prev: Common options,  Up: Top

3 Output of entire files
************************

These commands read and write entire files, possibly transforming them
in some way.

* Menu:

* cat invocation::              Concatenate and write files.
* tac invocation::              Concatenate and write files in reverse.
* nl invocation::               Number lines and write files.
* od invocation::               Write files in octal or other formats.
* base64 invocation::           Transform data into printable data.

File: coreutils.info,  Node: cat invocation,  Next: tac invocation,  Up: Output of entire files

3.1 `cat': Concatenate and write files
======================================

`cat' copies each FILE (`-' means standard input), or standard input if
none are given, to standard output.  Synopsis:

     cat [OPTION] [FILE]...

   The program accepts the following options.  Also see *note Common
options::.

`-A'
`--show-all'
     Equivalent to `-vET'.

`-b'
`--number-nonblank'
     Number all nonempty output lines, starting with 1.

`-e'
     Equivalent to `-vE'.

`-E'
`--show-ends'
     Display a `$' after the end of each line.

`-n'
`--number'
     Number all output lines, starting with 1.

`-s'
`--squeeze-blank'
     Suppress repeated adjacent empty lines; output just one empty line
     instead of several.

`-t'
     Equivalent to `-vT'.

`-T'
`--show-tabs'
     Display TAB characters as `^I'.

`-u'
     Ignored; for POSIX compatibility.

`-v'
`--show-nonprinting'
     Display control characters except for LFD and TAB using `^'
     notation and precede characters that have the high bit set with
     `M-'.


   On systems like MS-DOS that distinguish between text and binary
files, `cat' normally reads and writes in binary mode.  However, `cat'
reads in text mode if one of the options `-bensAE' is used or if `cat'
is reading from standard input and standard input is a terminal.
Similarly, `cat' writes in text mode if one of the options `-bensAE' is
used or if standard output is a terminal.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Examples:

     # Output f's contents, then standard input, then g's contents.
     cat f - g

     # Copy standard input to standard output.
     cat

File: coreutils.info,  Node: tac invocation,  Next: nl invocation,  Prev: cat invocation,  Up: Output of entire files

3.2 `tac': Concatenate and write files in reverse
=================================================

`tac' copies each FILE (`-' means standard input), or standard input if
none are given, to standard output, reversing the records (lines by
default) in each separately.  Synopsis:

     tac [OPTION]... [FILE]...

   "Records" are separated by instances of a string (newline by
default).  By default, this separator string is attached to the end of
the record that it follows in the file.

   The program accepts the following options.  Also see *note Common
options::.

`-b'
`--before'
     The separator is attached to the beginning of the record that it
     precedes in the file.

`-r'
`--regex'
     Treat the separator string as a regular expression.  Users of `tac'
     on MS-DOS/MS-Windows should note that, since `tac' reads files in
     binary mode, each line of a text file might end with a CR/LF pair
     instead of the Unix-style LF.

`-s SEPARATOR'
`--separator=SEPARATOR'
     Use SEPARATOR as the record separator, instead of newline.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: nl invocation,  Next: od invocation,  Prev: tac invocation,  Up: Output of entire files

3.3 `nl': Number lines and write files
======================================

`nl' writes each FILE (`-' means standard input), or standard input if
none are given, to standard output, with line numbers added to some or
all of the lines.  Synopsis:

     nl [OPTION]... [FILE]...

   `nl' decomposes its input into (logical) pages; by default, the line
number is reset to 1 at the top of each logical page.  `nl' treats all
of the input files as a single document; it does not reset line numbers
or logical pages between files.

   A logical page consists of three sections: header, body, and footer.
Any of the sections can be empty.  Each can be numbered in a different
style from the others.

   The beginnings of the sections of logical pages are indicated in the
input file by a line containing exactly one of these delimiter strings:

`\:\:\:'
     start of header;

`\:\:'
     start of body;

`\:'
     start of footer.

   The two characters from which these strings are made can be changed
from `\' and `:' via options (see below), but the pattern and length of
each string cannot be changed.

   A section delimiter is replaced by an empty line on output.  Any text
that comes before the first section delimiter string in the input file
is considered to be part of a body section, so `nl' treats a file that
contains no section delimiters as a single body section.

   The program accepts the following options.  Also see *note Common
options::.

`-b STYLE'
`--body-numbering=STYLE'
     Select the numbering style for lines in the body section of each
     logical page.  When a line is not numbered, the current line number
     is not incremented, but the line number separator character is
     still prepended to the line.  The styles are:

    `a'
          number all lines,

    `t'
          number only nonempty lines (default for body),

    `n'
          do not number lines (default for header and footer),

    `pBRE'
          number only lines that contain a match for the basic regular
          expression BRE.  *Note Regular Expressions: (grep)Regular
          Expressions.

`-d CD'
`--section-delimiter=CD'
     Set the section delimiter characters to CD; default is `\:'.  If
     only C is given, the second remains `:'.  (Remember to protect `\'
     or other metacharacters from shell expansion with quotes or extra
     backslashes.)

`-f STYLE'
`--footer-numbering=STYLE'
     Analogous to `--body-numbering'.

`-h STYLE'
`--header-numbering=STYLE'
     Analogous to `--body-numbering'.

`-i NUMBER'
`--line-increment=NUMBER'
     Increment line numbers by NUMBER (default 1).

`-l NUMBER'
`--join-blank-lines=NUMBER'
     Consider NUMBER (default 1) consecutive empty lines to be one
     logical line for numbering, and only number the last one.  Where
     fewer than NUMBER consecutive empty lines occur, do not number
     them.  An empty line is one that contains no characters, not even
     spaces or tabs.

`-n FORMAT'
`--number-format=FORMAT'
     Select the line numbering format (default is `rn'):

    `ln'
          left justified, no leading zeros;

    `rn'
          right justified, no leading zeros;

    `rz'
          right justified, leading zeros.

`-p'
`--no-renumber'
     Do not reset the line number at the start of a logical page.

`-s STRING'
`--number-separator=STRING'
     Separate the line number from the text line in the output with
     STRING (default is the TAB character).

`-v NUMBER'
`--starting-line-number=NUMBER'
     Set the initial line number on each logical page to NUMBER
     (default 1).

`-w NUMBER'
`--number-width=NUMBER'
     Use NUMBER characters for line numbers (default 6).


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: od invocation,  Next: base64 invocation,  Prev: nl invocation,  Up: Output of entire files

3.4 `od': Write files in octal or other formats
===============================================

`od' writes an unambiguous representation of each FILE (`-' means
standard input), or standard input if none are given.  Synopses:

     od [OPTION]... [FILE]...
     od [-abcdfilosx]... [FILE] [[+]OFFSET[.][b]]
     od [OPTION]... --traditional [FILE] [[+]OFFSET[.][b] [[+]LABEL[.][b]]]

   Each line of output consists of the offset in the input, followed by
groups of data from the file.  By default, `od' prints the offset in
octal, and each group of file data is a C `short int''s worth of input
printed as a single octal number.

   If OFFSET is given, it specifies how many input bytes to skip before
formatting and writing.  By default, it is interpreted as an octal
number, but the optional trailing decimal point causes it to be
interpreted as decimal.  If no decimal is specified and the offset
begins with `0x' or `0X' it is interpreted as a hexadecimal number.  If
there is a trailing `b', the number of bytes skipped will be OFFSET
multiplied by 512.

   If a command is of both the first and second forms, the second form
is assumed if the last operand begins with `+' or (if there are two
operands) a digit.  For example, in `od foo 10' and `od +10' the `10'
is an offset, whereas in `od 10' the `10' is a file name.

   The program accepts the following options.  Also see *note Common
options::.

`-A RADIX'
`--address-radix=RADIX'
     Select the base in which file offsets are printed.  RADIX can be
     one of the following:

    `d'
          decimal;

    `o'
          octal;

    `x'
          hexadecimal;

    `n'
          none (do not print offsets).

     The default is octal.

`-j BYTES'
`--skip-bytes=BYTES'
     Skip BYTES input bytes before formatting and writing.  If BYTES
     begins with `0x' or `0X', it is interpreted in hexadecimal;
     otherwise, if it begins with `0', in octal; otherwise, in decimal.
     BYTES may be, or may be an integer optionally followed by, one of
     the following multiplicative suffixes:
          `b'  =>            512 ("blocks")
          `KB' =>           1000 (KiloBytes)
          `K'  =>           1024 (KibiBytes)
          `MB' =>      1000*1000 (MegaBytes)
          `M'  =>      1024*1024 (MebiBytes)
          `GB' => 1000*1000*1000 (GigaBytes)
          `G'  => 1024*1024*1024 (GibiBytes)
     and so on for `T', `P', `E', `Z', and `Y'.

`-N BYTES'
`--read-bytes=BYTES'
     Output at most BYTES bytes of the input.  Prefixes and suffixes on
     `bytes' are interpreted as for the `-j' option.

`-S BYTES'
`--strings[=BYTES]'
     Instead of the normal output, output only "string constants": at
     least BYTES consecutive ASCII graphic characters, followed by a
     zero byte (ASCII NUL).  Prefixes and suffixes on `bytes' are
     interpreted as for the `-j' option.

     If N is omitted with `--strings', the default is 3.

`-t TYPE'
`--format=TYPE'
     Select the format in which to output the file data.  TYPE is a
     string of one or more of the below type indicator characters.  If
     you include more than one type indicator character in a single TYPE
     string, or use this option more than once, `od' writes one copy of
     each output line using each of the data types that you specified,
     in the order that you specified.

     Adding a trailing "z" to any type specification appends a display
     of the ASCII character representation of the printable characters
     to the output line generated by the type specification.

    `a'
          named character, ignoring high-order bit

    `c'
          ASCII character or backslash escape,

    `d'
          signed decimal

    `f'
          floating point

    `o'
          octal

    `u'
          unsigned decimal

    `x'
          hexadecimal

     The type `a' outputs things like `sp' for space, `nl' for newline,
     and `nul' for a zero byte.  Only the least significant seven bits
     of each byte is used; the high-order bit is ignored.  Type `c'
     outputs ` ', `\n', and `\0', respectively.

     Except for types `a' and `c', you can specify the number of bytes
     to use in interpreting each number in the given data type by
     following the type indicator character with a decimal integer.
     Alternately, you can specify the size of one of the C compiler's
     built-in data types by following the type indicator character with
     one of the following characters.  For integers (`d', `o', `u',
     `x'):

    `C'
          char

    `S'
          short

    `I'
          int

    `L'
          long

     For floating point (`f'):

    F
          float

    D
          double

    L
          long double

`-v'
`--output-duplicates'
     Output consecutive lines that are identical.  By default, when two
     or more consecutive output lines would be identical, `od' outputs
     only the first line, and puts just an asterisk on the following
     line to indicate the elision.

`-w[N]'
`--width[=N]'
     Dump `n' input bytes per output line.  This must be a multiple of
     the least common multiple of the sizes associated with the
     specified output types.

     If this option is not given at all, the default is 16.  If N is
     omitted, the default is 32.


   The next several options are shorthands for format specifications.
GNU `od' accepts any combination of shorthands and format specification
options.  These options accumulate.

`-a'
     Output as named characters.  Equivalent to `-t a'.

`-b'
     Output as octal bytes.  Equivalent to `-t o1'.

`-c'
     Output as ASCII characters or backslash escapes.  Equivalent to
     `-t c'.

`-d'
     Output as unsigned decimal two-byte units.  Equivalent to `-t u2'.

`-f'
     Output as floats.  Equivalent to `-t fF'.

`-i'
     Output as decimal ints.  Equivalent to `-t dI'.

`-l'
     Output as decimal long ints.  Equivalent to `-t dL'.

`-o'
     Output as octal two-byte units.  Equivalent to `-t o2'.

`-s'
     Output as decimal two-byte units.  Equivalent to `-t d2'.

`-x'
     Output as hexadecimal two-byte units.  Equivalent to `-t x2'.

`--traditional'
     Recognize the non-option label argument that traditional `od'
     accepted.  The following syntax:

          od --traditional [FILE] [[+]OFFSET[.][b] [[+]LABEL[.][b]]]

     can be used to specify at most one file and optional arguments
     specifying an offset and a pseudo-start address, LABEL.  The LABEL
     argument is interpreted just like OFFSET, but it specifies an
     initial pseudo-address.  The pseudo-addresses are displayed in
     parentheses following any normal address.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: base64 invocation,  Prev: od invocation,  Up: Output of entire files

3.5 `base64': Transform data into printable data
================================================

`base64' transforms data read from a file, or standard input, into (or
from) base64 encoded form.  The base64 encoded form uses printable
ASCII characters to represent binary data.  Synopses:

     base64 [OPTION]... [FILE]
     base64 --decode [OPTION]... [FILE]

   The base64 encoding expands data to roughly 133% of the original.
The format conforms to RFC 4648
(ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt).

   The program accepts the following options.  Also see *note Common
options::.

`-w COLS'
`--wrap=COLS'
     During encoding, wrap lines after COLS characters.  This must be a
     positive number.

     The default is to wrap after 76 characters.  Use the value 0 to
     disable line wrapping altogether.

`-d'
`--decode'
     Change the mode of operation, from the default of encoding data, to
     decoding data.  Input is expected to be base64 encoded data, and
     the output will be the original data.

`-i'
`--ignore-garbage'
     When decoding, newlines are always accepted.  During decoding,
     ignore unrecognized bytes, to permit distorted data to be decoded.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: Formatting file contents,  Next: Output of parts of files,  Prev: Output of entire files,  Up: Top

4 Formatting file contents
**************************

These commands reformat the contents of files.

* Menu:

* fmt invocation::              Reformat paragraph text.
* pr invocation::               Paginate or columnate files for printing.
* fold invocation::             Wrap input lines to fit in specified width.

File: coreutils.info,  Node: fmt invocation,  Next: pr invocation,  Up: Formatting file contents

4.1 `fmt': Reformat paragraph text
==================================

`fmt' fills and joins lines to produce output lines of (at most) a
given number of characters (75 by default).  Synopsis:

     fmt [OPTION]... [FILE]...

   `fmt' reads from the specified FILE arguments (or standard input if
none are given), and writes to standard output.

   By default, blank lines, spaces between words, and indentation are
preserved in the output; successive input lines with different
indentation are not joined; tabs are expanded on input and introduced on
output.

   `fmt' prefers breaking lines at the end of a sentence, and tries to
avoid line breaks after the first word of a sentence or before the last
word of a sentence.  A "sentence break" is defined as either the end of
a paragraph or a word ending in any of `.?!', followed by two spaces or
end of line, ignoring any intervening parentheses or quotes.  Like TeX,
`fmt' reads entire "paragraphs" before choosing line breaks; the
algorithm is a variant of that given by Donald E. Knuth and Michael F.
Plass in "Breaking Paragraphs Into Lines", `Software--Practice &
Experience' 11, 11 (November 1981), 1119-1184.

   The program accepts the following options.  Also see *note Common
options::.

`-c'
`--crown-margin'
     "Crown margin" mode: preserve the indentation of the first two
     lines within a paragraph, and align the left margin of each
     subsequent line with that of the second line.

`-t'
`--tagged-paragraph'
     "Tagged paragraph" mode: like crown margin mode, except that if
     indentation of the first line of a paragraph is the same as the
     indentation of the second, the first line is treated as a one-line
     paragraph.

`-s'
`--split-only'
     Split lines only.  Do not join short lines to form longer ones.
     This prevents sample lines of code, and other such "formatted"
     text from being unduly combined.

`-u'
`--uniform-spacing'
     Uniform spacing.  Reduce spacing between words to one space, and
     spacing between sentences to two spaces.

`-WIDTH'
`-w WIDTH'
`--width=WIDTH'
     Fill output lines up to WIDTH characters (default 75).  `fmt'
     initially tries to make lines about 7% shorter than this, to give
     it room to balance line lengths.

`-p PREFIX'
`--prefix=PREFIX'
     Only lines beginning with PREFIX (possibly preceded by whitespace)
     are subject to formatting.  The prefix and any preceding
     whitespace are stripped for the formatting and then re-attached to
     each formatted output line.  One use is to format certain kinds of
     program comments, while leaving the code unchanged.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: pr invocation,  Next: fold invocation,  Prev: fmt invocation,  Up: Formatting file contents

4.2 `pr': Paginate or columnate files for printing
==================================================

`pr' writes each FILE (`-' means standard input), or standard input if
none are given, to standard output, paginating and optionally
outputting in multicolumn format; optionally merges all FILEs, printing
all in parallel, one per column.  Synopsis:

     pr [OPTION]... [FILE]...

   By default, a 5-line header is printed at each page: two blank lines;
a line with the date, the file name, and the page count; and two more
blank lines.  A footer of five blank lines is also printed.  The
default PAGE_LENGTH is 66 lines.  The default number of text lines is
therefore 56.  The text line of the header takes the form `DATE STRING
PAGE', with spaces inserted around STRING so that the line takes up the
full PAGE_WIDTH.  Here, DATE is the date (see the `-D' or
`--date-format' option for details), STRING is the centered header
string, and PAGE identifies the page number.  The `LC_MESSAGES' locale
category affects the spelling of PAGE; in the default C locale, it is
`Page NUMBER' where NUMBER is the decimal page number.

   Form feeds in the input cause page breaks in the output.  Multiple
form feeds produce empty pages.

   Columns are of equal width, separated by an optional string (default
is `space').  For multicolumn output, lines will always be truncated to
PAGE_WIDTH (default 72), unless you use the `-J' option.  For single
column output no line truncation occurs by default.  Use `-W' option to
truncate lines in that case.

   The following changes were made in version 1.22i and apply to later
versions of `pr':  - Brian
   * Some small LETTER OPTIONS (`-s', `-w') have been redefined for
     better POSIX compliance.  The output of some further cases has
     been adapted to other Unix systems.  These changes are not
     compatible with earlier versions of the program.

   * Some NEW CAPITAL LETTER options (`-J', `-S', `-W') have been
     introduced to turn off unexpected interferences of small letter
     options.  The `-N' option and the second argument LAST_PAGE of
     `+FIRST_PAGE' offer more flexibility.  The detailed handling of
     form feeds set in the input files requires the `-T' option.

   * Capital letter options override small letter ones.

   * Some of the option-arguments (compare `-s', `-e', `-i', `-n')
     cannot be specified as separate arguments from the preceding
     option letter (already stated in the POSIX specification).

   The program accepts the following options.  Also see *note Common
options::.

`+FIRST_PAGE[:LAST_PAGE]'
`--pages=FIRST_PAGE[:LAST_PAGE]'
     Begin printing with page FIRST_PAGE and stop with LAST_PAGE.
     Missing `:LAST_PAGE' implies end of file.  While estimating the
     number of skipped pages each form feed in the input file results
     in a new page.  Page counting with and without `+FIRST_PAGE' is
     identical.  By default, counting starts with the first page of
     input file (not first page printed).  Line numbering may be
     altered by `-N' option.

`-COLUMN'
`--columns=COLUMN'
     With each single FILE, produce COLUMN columns of output (default
     is 1) and print columns down, unless `-a' is used.  The column
     width is automatically decreased as COLUMN increases; unless you
     use the `-W/-w' option to increase PAGE_WIDTH as well.  This
     option might well cause some lines to be truncated.  The number of
     lines in the columns on each page are balanced.  The options `-e'
     and `-i' are on for multiple text-column output.  Together with
     `-J' option column alignment and line truncation is turned off.
     Lines of full length are joined in a free field format and `-S'
     option may set field separators.  `-COLUMN' may not be used with
     `-m' option.

`-a'
`--across'
     With each single FILE, print columns across rather than down.  The
     `-COLUMN' option must be given with COLUMN greater than one.  If a
     line is too long to fit in a column, it is truncated.

`-c'
`--show-control-chars'
     Print control characters using hat notation (e.g., `^G'); print
     other nonprinting characters in octal backslash notation.  By
     default, nonprinting characters are not changed.

`-d'
`--double-space'
     Double space the output.

`-D FORMAT'
`--date-format=FORMAT'
     Format header dates using FORMAT, using the same conventions as
     for the command `date +FORMAT'; *Note date invocation::.  Except
     for directives, which start with `%', characters in FORMAT are
     printed unchanged.  You can use this option to specify an
     arbitrary string in place of the header date, e.g.,
     `--date-format="Monday morning"'.

     The default date format is `%Y-%m-%d %H:%M' (for example,
     `2001-12-04 23:59'); but if the `POSIXLY_CORRECT' environment
     variable is set and the `LC_TIME' locale category specifies the
     POSIX locale, the default is `%b %e %H:%M %Y' (for example, `Dec
     4 23:59 2001'.

     Time stamps are listed according to the time zone rules specified
     by the `TZ' environment variable, or by the system default rules if
     `TZ' is not set.  *Note Specifying the Time Zone with `TZ':
     (libc)TZ Variable.

`-e[IN-TABCHAR[IN-TABWIDTH]]'
`--expand-tabs[=IN-TABCHAR[IN-TABWIDTH]]'
     Expand TABs to spaces on input.  Optional argument IN-TABCHAR is
     the input tab character (default is the TAB character).  Second
     optional argument IN-TABWIDTH is the input tab character's width
     (default is 8).

`-f'
`-F'
`--form-feed'
     Use a form feed instead of newlines to separate output pages.
     This does not alter the default page length of 66 lines.

`-h HEADER'
`--header=HEADER'
     Replace the file name in the header with the centered string
     HEADER.  When using the shell, HEADER should be quoted and should
     be separated from `-h' by a space.

`-i[OUT-TABCHAR[OUT-TABWIDTH]]'
`--output-tabs[=OUT-TABCHAR[OUT-TABWIDTH]]'
     Replace spaces with TABs on output.  Optional argument OUT-TABCHAR
     is the output tab character (default is the TAB character).
     Second optional argument OUT-TABWIDTH is the output tab
     character's width (default is 8).

`-J'
`--join-lines'
     Merge lines of full length.  Used together with the column options
     `-COLUMN', `-a -COLUMN' or `-m'.  Turns off `-W/-w' line
     truncation; no column alignment used; may be used with
     `--sep-string[=STRING]'.  `-J' has been introduced (together with
     `-W' and `--sep-string') to disentangle the old (POSIX-compliant)
     options `-w' and `-s' along with the three column options.

`-l PAGE_LENGTH'
`--length=PAGE_LENGTH'
     Set the page length to PAGE_LENGTH (default 66) lines, including
     the lines of the header [and the footer].  If PAGE_LENGTH is less
     than or equal to 10, the header and footer are omitted, as if the
     `-t' option had been given.

`-m'
`--merge'
     Merge and print all FILEs in parallel, one in each column.  If a
     line is too long to fit in a column, it is truncated, unless the
     `-J' option is used.  `--sep-string[=STRING]' may be used.  Empty
     pages in some FILEs (form feeds set) produce empty columns, still
     marked by STRING.  The result is a continuous line numbering and
     column marking throughout the whole merged file.  Completely empty
     merged pages show no separators or line numbers.  The default
     header becomes `DATE PAGE' with spaces inserted in the middle; this
     may be used with the `-h' or `--header' option to fill up the
     middle blank part.

`-n[NUMBER-SEPARATOR[DIGITS]]'
`--number-lines[=NUMBER-SEPARATOR[DIGITS]]'
     Provide DIGITS digit line numbering (default for DIGITS is 5).
     With multicolumn output the number occupies the first DIGITS
     column positions of each text column or only each line of `-m'
     output.  With single column output the number precedes each line
     just as `-m' does.  Default counting of the line numbers starts
     with the first line of the input file (not the first line printed,
     compare the `--page' option and `-N' option).  Optional argument
     NUMBER-SEPARATOR is the character appended to the line number to
     separate it from the text followed.  The default separator is the
     TAB character.  In a strict sense a TAB is always printed with
     single column output only.  The TAB width varies with the TAB
     position, e.g., with the left MARGIN specified by `-o' option.
     With multicolumn output priority is given to `equal width of
     output columns' (a POSIX specification).  The TAB width is fixed
     to the value of the first column and does not change with
     different values of left MARGIN.  That means a fixed number of
     spaces is always printed in the place of the NUMBER-SEPARATOR TAB.
     The tabification depends upon the output position.

`-N LINE_NUMBER'
`--first-line-number=LINE_NUMBER'
     Start line counting with the number LINE_NUMBER at first line of
     first page printed (in most cases not the first line of the input
     file).

`-o MARGIN'
`--indent=MARGIN'
     Indent each line with a margin MARGIN spaces wide (default is
     zero).  The total page width is the size of the margin plus the
     PAGE_WIDTH set with the `-W/-w' option.  A limited overflow may
     occur with numbered single column output (compare `-n' option).

`-r'
`--no-file-warnings'
     Do not print a warning message when an argument FILE cannot be
     opened.  (The exit status will still be nonzero, however.)

`-s[CHAR]'
`--separator[=CHAR]'
     Separate columns by a single character CHAR.  The default for CHAR
     is the TAB character without `-w' and `no character' with `-w'.
     Without `-s' the default separator `space' is set.  `-s[char]'
     turns off line truncation of all three column options
     (`-COLUMN'|`-a -COLUMN'|`-m') unless `-w' is set.  This is a
     POSIX-compliant formulation.

`-SSTRING'
`--sep-string[=STRING]'
     Use STRING to separate output columns.  The `-S' option doesn't
     affect the `-W/-w' option, unlike the `-s' option which does.  It
     does not affect line truncation or column alignment.  Without
     `-S', and with `-J', `pr' uses the default output separator, TAB.
     Without `-S' or `-J', `pr' uses a `space' (same as `-S" "').
     `--sep-string' with no `=STRING' is equivalent to
     `--sep-string=""'.

`-t'
`--omit-header'
     Do not print the usual header [and footer] on each page, and do
     not fill out the bottom of pages (with blank lines or a form
     feed).  No page structure is produced, but form feeds set in the
     input files are retained.  The predefined pagination is not
     changed.  `-t' or `-T' may be useful together with other options;
     e.g.: `-t -e4', expand TAB characters in the input file to 4
     spaces but don't make any other changes.  Use of `-t' overrides
     `-h'.

`-T'
`--omit-pagination'
     Do not print header [and footer].  In addition eliminate all form
     feeds set in the input files.

`-v'
`--show-nonprinting'
     Print nonprinting characters in octal backslash notation.

`-w PAGE_WIDTH'
`--width=PAGE_WIDTH'
     Set page width to PAGE_WIDTH characters for multiple text-column
     output only (default for PAGE_WIDTH is 72).  `-s[CHAR]' turns off
     the default page width and any line truncation and column
     alignment.  Lines of full length are merged, regardless of the
     column options set.  No PAGE_WIDTH setting is possible with single
     column output.  A POSIX-compliant formulation.

`-W PAGE_WIDTH'
`--page_width=PAGE_WIDTH'
     Set the page width to PAGE_WIDTH characters.  That's valid with and
     without a column option.  Text lines are truncated, unless `-J' is
     used.  Together with one of the three column options (`-COLUMN',
     `-a -COLUMN' or `-m') column alignment is always used.  The
     separator options `-S' or `-s' don't affect the `-W' option.
     Default is 72 characters.  Without `-W PAGE_WIDTH' and without any
     of the column options NO line truncation is used (defined to keep
     downward compatibility and to meet most frequent tasks).  That's
     equivalent to `-W 72 -J'.  The header line is never truncated.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: fold invocation,  Prev: pr invocation,  Up: Formatting file contents

4.3 `fold': Wrap input lines to fit in specified width
======================================================

`fold' writes each FILE (`-' means standard input), or standard input
if none are given, to standard output, breaking long lines.  Synopsis:

     fold [OPTION]... [FILE]...

   By default, `fold' breaks lines wider than 80 columns.  The output
is split into as many lines as necessary.

   `fold' counts screen columns by default; thus, a tab may count more
than one column, backspace decreases the column count, and carriage
return sets the column to zero.

   The program accepts the following options.  Also see *note Common
options::.

`-b'
`--bytes'
     Count bytes rather than columns, so that tabs, backspaces, and
     carriage returns are each counted as taking up one column, just
     like other characters.

`-s'
`--spaces'
     Break at word boundaries: the line is broken after the last blank
     before the maximum line length.  If the line contains no such
     blanks, the line is broken at the maximum line length as usual.

`-w WIDTH'
`--width=WIDTH'
     Use a maximum line length of WIDTH columns instead of 80.

     For compatibility `fold' supports an obsolete option syntax
     `-WIDTH'.  New scripts should use `-w WIDTH' instead.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: Output of parts of files,  Next: Summarizing files,  Prev: Formatting file contents,  Up: Top

5 Output of parts of files
**************************

These commands output pieces of the input.

* Menu:

* head invocation::             Output the first part of files.
* tail invocation::             Output the last part of files.
* split invocation::            Split a file into fixed-size pieces.
* csplit invocation::           Split a file into context-determined pieces.

File: coreutils.info,  Node: head invocation,  Next: tail invocation,  Up: Output of parts of files

5.1 `head': Output the first part of files
==========================================

`head' prints the first part (10 lines by default) of each FILE; it
reads from standard input if no files are given or when given a FILE of
`-'.  Synopsis:

     head [OPTION]... [FILE]...

   If more than one FILE is specified, `head' prints a one-line header
consisting of:

     ==> FILE NAME <==

before the output for each FILE.

   The program accepts the following options.  Also see *note Common
options::.

`-c K'
`--bytes=K'
     Print the first K bytes, instead of initial lines.  However, if K
     starts with a `-', print all but the last K bytes of each file.  K
     may be, or may be an integer optionally followed by, one of the
     following multiplicative suffixes:
          `b'  =>            512 ("blocks")
          `KB' =>           1000 (KiloBytes)
          `K'  =>           1024 (KibiBytes)
          `MB' =>      1000*1000 (MegaBytes)
          `M'  =>      1024*1024 (MebiBytes)
          `GB' => 1000*1000*1000 (GigaBytes)
          `G'  => 1024*1024*1024 (GibiBytes)
     and so on for `T', `P', `E', `Z', and `Y'.

`-n K'
`--lines=K'
     Output the first K lines.  However, if K starts with a `-', print
     all but the last K lines of each file.  Size multiplier suffixes
     are the same as with the `-c' option.

`-q'
`--quiet'
`--silent'
     Never print file name headers.

`-v'
`--verbose'
     Always print file name headers.


   For compatibility `head' also supports an obsolete option syntax
`-COUNTOPTIONS', which is recognized only if it is specified first.
COUNT is a decimal number optionally followed by a size letter (`b',
`k', `m') as in `-c', or `l' to mean count by lines, or other option
letters (`cqv').  Scripts intended for standard hosts should use `-c
COUNT' or `-n COUNT' instead.  If your script must also run on hosts
that support only the obsolete syntax, it is usually simpler to avoid
`head', e.g., by using `sed 5q' instead of `head -5'.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: tail invocation,  Next: split invocation,  Prev: head invocation,  Up: Output of parts of files

5.2 `tail': Output the last part of files
=========================================

`tail' prints the last part (10 lines by default) of each FILE; it
reads from standard input if no files are given or when given a FILE of
`-'.  Synopsis:

     tail [OPTION]... [FILE]...

   If more than one FILE is specified, `tail' prints a one-line header
consisting of:

     ==> FILE NAME <==

before the output for each FILE.

   GNU `tail' can output any amount of data (some other versions of
`tail' cannot).  It also has no `-r' option (print in reverse), since
reversing a file is really a different job from printing the end of a
file; BSD `tail' (which is the one with `-r') can only reverse files
that are at most as large as its buffer, which is typically 32 KiB.  A
more reliable and versatile way to reverse files is the GNU `tac'
command.

   The program accepts the following options.  Also see *note Common
options::.

`-c K'
`--bytes=K'
     Output the last K bytes, instead of final lines.  However, if K
     starts with a `+', start printing with the Kth byte from the start
     of each file, instead of from the end.  K may be, or may be an
     integer optionally followed by, one of the following
     multiplicative suffixes:
          `b'  =>            512 ("blocks")
          `KB' =>           1000 (KiloBytes)
          `K'  =>           1024 (KibiBytes)
          `MB' =>      1000*1000 (MegaBytes)
          `M'  =>      1024*1024 (MebiBytes)
          `GB' => 1000*1000*1000 (GigaBytes)
          `G'  => 1024*1024*1024 (GibiBytes)
     and so on for `T', `P', `E', `Z', and `Y'.

`-f'
`--follow[=HOW]'
     Loop forever trying to read more characters at the end of the file,
     presumably because the file is growing.  If more than one file is
     given, `tail' prints a header whenever it gets output from a
     different file, to indicate which file that output is from.

     There are two ways to specify how you'd like to track files with
     this option, but that difference is noticeable only when a
     followed file is removed or renamed.  If you'd like to continue to
     track the end of a growing file even after it has been unlinked,
     use `--follow=descriptor'.  This is the default behavior, but it
     is not useful if you're tracking a log file that may be rotated
     (removed or renamed, then reopened).  In that case, use
     `--follow=name' to track the named file, perhaps by reopening it
     periodically to see if it has been removed and recreated by some
     other program.  Note that the inotify-based implementation handles
     this case without the need for any periodic reopening.

     No matter which method you use, if the tracked file is determined
     to have shrunk, `tail' prints a message saying the file has been
     truncated and resumes tracking the end of the file from the
     newly-determined endpoint.

     When a file is removed, `tail''s behavior depends on whether it is
     following the name or the descriptor.  When following by name,
     tail can detect that a file has been removed and gives a message
     to that effect, and if `--retry' has been specified it will
     continue checking periodically to see if the file reappears.  When
     following a descriptor, tail does not detect that the file has
     been unlinked or renamed and issues no message;  even though the
     file may no longer be accessible via its original name, it may
     still be growing.

     The option values `descriptor' and `name' may be specified only
     with the long form of the option, not with `-f'.

     The `-f' option is ignored if no FILE operand is specified and
     standard input is a FIFO or a pipe.  Likewise, the `-f' option has
     no effect for any operand specified as `-', when standard input is
     a FIFO or a pipe.

     With kernel inotify support, output is triggered by file changes
     and is generally very prompt.  Otherwise, `tail' sleeps for one
     second between checks-- use `--sleep-interval=NUMBER' to change
     that default--which can make the output appear slightly less
     responsive or bursty.  When using tail without inotify support,
     you can make it more responsive by using a sub-second sleep
     interval, e.g., via an alias like this:

          alias tail='tail -s.1'

`-F'
     This option is the same as `--follow=name --retry'.  That is, tail
     will attempt to reopen a file when it is removed.  Should this
     fail, tail will keep trying until it becomes accessible again.

`--retry'
     This option is useful mainly when following by name (i.e., with
     `--follow=name').  Without this option, when tail encounters a
     file that doesn't exist or is otherwise inaccessible, it reports
     that fact and never checks it again.

`--sleep-interval=NUMBER'
     Change the number of seconds to wait between iterations (the
     default is 1.0).  During one iteration, every specified file is
     checked to see if it has changed size.  Historical implementations
     of `tail' have required that NUMBER be an integer.  However, GNU
     `tail' accepts an arbitrary floating point number (using a period
     before any fractional digits).  When `tail' uses inotify, this
     polling-related option is usually ignored. However, if you also
     specify `--pid=P', `tail' checks whether process P is alive at
     least every NUMBER seconds.

`--pid=PID'
     When following by name or by descriptor, you may specify the
     process ID, PID, of the sole writer of all FILE arguments.  Then,
     shortly after that process terminates, tail will also terminate.
     This will work properly only if the writer and the tailing process
     are running on the same machine.  For example, to save the output
     of a build in a file and to watch the file grow, if you invoke
     `make' and `tail' like this then the tail process will stop when
     your build completes.  Without this option, you would have had to
     kill the `tail -f' process yourself.

          $ make >& makerr & tail --pid=$! -f makerr

     If you specify a PID that is not in use or that does not correspond
     to the process that is writing to the tailed files, then `tail'
     may terminate long before any FILEs stop growing or it may not
     terminate until long after the real writer has terminated.  Note
     that `--pid' cannot be supported on some systems; `tail' will
     print a warning if this is the case.

`--max-unchanged-stats=N'
     When tailing a file by name, if there have been N (default
     n=5) consecutive iterations for which the file has not changed,
     then `open'/`fstat' the file to determine if that file name is
     still associated with the same device/inode-number pair as before.
     When following a log file that is rotated, this is approximately
     the number of seconds between when tail prints the last
     pre-rotation lines and when it prints the lines that have
     accumulated in the new log file.  This option is meaningful only
     when polling (i.e., without inotify) and when following by name.

`-n K'
`--lines=K'
     Output the last K lines.  However, if K starts with a `+', start
     printing with the Kth line from the start of each file, instead of
     from the end.  Size multiplier suffixes are the same as with the
     `-c' option.

`-q'
`--quiet'
`--silent'
     Never print file name headers.

`-v'
`--verbose'
     Always print file name headers.


   For compatibility `tail' also supports an obsolete usage `tail
-[COUNT][bcl][f] [FILE]', which is recognized only if it does not
conflict with the usage described above.  This obsolete form uses
exactly one option and at most one file.  In the option, COUNT is an
optional decimal number optionally followed by a size letter (`b', `c',
`l') to mean count by 512-byte blocks, bytes, or lines, optionally
followed by `f' which has the same meaning as `-f'.

   On older systems, the leading `-' can be replaced by `+' in the
obsolete option syntax with the same meaning as in counts, and obsolete
usage overrides normal usage when the two conflict.  This obsolete
behavior can be enabled or disabled with the `_POSIX2_VERSION'
environment variable (*note Standards conformance::).

   Scripts intended for use on standard hosts should avoid obsolete
syntax and should use `-c COUNT[b]', `-n COUNT', and/or `-f' instead.
If your script must also run on hosts that support only the obsolete
syntax, you can often rewrite it to avoid problematic usages, e.g., by
using `sed -n '$p'' rather than `tail -1'.  If that's not possible, the
script can use a test like `if tail -c +1 </dev/null >/dev/null 2>&1;
then ...' to decide which syntax to use.

   Even if your script assumes the standard behavior, you should still
beware usages whose behaviors differ depending on the POSIX version.
For example, avoid `tail - main.c', since it might be interpreted as
either `tail main.c' or as `tail -- - main.c'; avoid `tail -c 4', since
it might mean either `tail -c4' or `tail -c 10 4'; and avoid `tail +4',
since it might mean either `tail ./+4' or `tail -n +4'.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: split invocation,  Next: csplit invocation,  Prev: tail invocation,  Up: Output of parts of files

5.3 `split': Split a file into fixed-size pieces
================================================

`split' creates output files containing consecutive sections of INPUT
(standard input if none is given or INPUT is `-').  Synopsis:

     split [OPTION] [INPUT [PREFIX]]

   By default, `split' puts 1000 lines of INPUT (or whatever is left
over for the last section), into each output file.

   The output files' names consist of PREFIX (`x' by default) followed
by a group of characters (`aa', `ab', ... by default), such that
concatenating the output files in traditional sorted order by file name
produces the original input file.  If the output file names are
exhausted, `split' reports an error without deleting the output files
that it did create.

   The program accepts the following options.  Also see *note Common
options::.

`-l LINES'
`--lines=LINES'
     Put LINES lines of INPUT into each output file.

     For compatibility `split' also supports an obsolete option syntax
     `-LINES'.  New scripts should use `-l LINES' instead.

`-b SIZE'
`--bytes=SIZE'
     Put SIZE bytes of INPUT into each output file.  SIZE may be, or
     may be an integer optionally followed by, one of the following
     multiplicative suffixes:
          `b'  =>            512 ("blocks")
          `KB' =>           1000 (KiloBytes)
          `K'  =>           1024 (KibiBytes)
          `MB' =>      1000*1000 (MegaBytes)
          `M'  =>      1024*1024 (MebiBytes)
          `GB' => 1000*1000*1000 (GigaBytes)
          `G'  => 1024*1024*1024 (GibiBytes)
     and so on for `T', `P', `E', `Z', and `Y'.

`-C SIZE'
`--line-bytes=SIZE'
     Put into each output file as many complete lines of INPUT as
     possible without exceeding SIZE bytes.  Individual lines longer
     than SIZE bytes are broken into multiple files.  SIZE has the same
     format as for the `--bytes' option.

`-a LENGTH'
`--suffix-length=LENGTH'
     Use suffixes of length LENGTH.  The default LENGTH is 2.

`-d'
`--numeric-suffixes'
     Use digits in suffixes rather than lower-case letters.

`--verbose'
     Write a diagnostic just before each output file is opened.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: csplit invocation,  Prev: split invocation,  Up: Output of parts of files

5.4 `csplit': Split a file into context-determined pieces
=========================================================

`csplit' creates zero or more output files containing sections of INPUT
(standard input if INPUT is `-').  Synopsis:

     csplit [OPTION]... INPUT PATTERN...

   The contents of the output files are determined by the PATTERN
arguments, as detailed below.  An error occurs if a PATTERN argument
refers to a nonexistent line of the input file (e.g., if no remaining
line matches a given regular expression).  After every PATTERN has been
matched, any remaining input is copied into one last output file.

   By default, `csplit' prints the number of bytes written to each
output file after it has been created.

   The types of pattern arguments are:

`N'
     Create an output file containing the input up to but not including
     line N (a positive integer).  If followed by a repeat count, also
     create an output file containing the next N lines of the input
     file once for each repeat.

`/REGEXP/[OFFSET]'
     Create an output file containing the current line up to (but not
     including) the next line of the input file that contains a match
     for REGEXP.  The optional OFFSET is an integer.  If it is given,
     the input up to (but not including) the matching line plus or
     minus OFFSET is put into the output file, and the line after that
     begins the next section of input.

`%REGEXP%[OFFSET]'
     Like the previous type, except that it does not create an output
     file, so that section of the input file is effectively ignored.

`{REPEAT-COUNT}'
     Repeat the previous pattern REPEAT-COUNT additional times.  The
     REPEAT-COUNT can either be a positive integer or an asterisk,
     meaning repeat as many times as necessary until the input is
     exhausted.


   The output files' names consist of a prefix (`xx' by default)
followed by a suffix.  By default, the suffix is an ascending sequence
of two-digit decimal numbers from `00' to `99'.  In any case,
concatenating the output files in sorted order by file name produces the
original input file.

   By default, if `csplit' encounters an error or receives a hangup,
interrupt, quit, or terminate signal, it removes any output files that
it has created so far before it exits.

   The program accepts the following options.  Also see *note Common
options::.

`-f PREFIX'
`--prefix=PREFIX'
     Use PREFIX as the output file name prefix.

`-b SUFFIX'
`--suffix=SUFFIX'
     Use SUFFIX as the output file name suffix.  When this option is
     specified, the suffix string must include exactly one
     `printf(3)'-style conversion specification, possibly including
     format specification flags, a field width, a precision
     specifications, or all of these kinds of modifiers.  The format
     letter must convert a binary integer argument to readable form;
     thus, only `d', `i', `u', `o', `x', and `X' conversions are
     allowed.  The entire SUFFIX is given (with the current output file
     number) to `sprintf(3)' to form the file name suffixes for each of
     the individual output files in turn.  If this option is used, the
     `--digits' option is ignored.

`-n DIGITS'
`--digits=DIGITS'
     Use output file names containing numbers that are DIGITS digits
     long instead of the default 2.

`-k'
`--keep-files'
     Do not remove output files when errors are encountered.

`-z'
`--elide-empty-files'
     Suppress the generation of zero-length output files.  (In cases
     where the section delimiters of the input file are supposed to
     mark the first lines of each of the sections, the first output
     file will generally be a zero-length file unless you use this
     option.)  The output file sequence numbers always run
     consecutively starting from 0, even when this option is specified.

`-s'
`-q'
`--silent'
`--quiet'
     Do not print counts of output file sizes.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Here is an example of its usage.  First, create an empty directory
for the exercise, and cd into it:

     $ mkdir d && cd d

   Now, split the sequence of 1..14 on lines that end with 0 or 5:

     $ seq 14 | csplit - '/[05]$/' '{*}'
     8
     10
     15

   Each number printed above is the size of an output file that csplit
has just created.  List the names of those output files:

     $ ls
     xx00  xx01  xx02

   Use `head' to show their contents:

     $ head xx*
     ==> xx00 <==
     1
     2
     3
     4

     ==> xx01 <==
     5
     6
     7
     8
     9

     ==> xx02 <==
     10
     11
     12
     13
     14

File: coreutils.info,  Node: Summarizing files,  Next: Operating on sorted files,  Prev: Output of parts of files,  Up: Top

6 Summarizing files
*******************

These commands generate just a few numbers representing entire contents
of files.

* Menu:

* wc invocation::               Print newline, word, and byte counts.
* sum invocation::              Print checksum and block counts.
* cksum invocation::            Print CRC checksum and byte counts.
* md5sum invocation::           Print or check MD5 digests.
* sha1sum invocation::          Print or check SHA-1 digests.
* sha2 utilities::              Print or check SHA-2 digests.

File: coreutils.info,  Node: wc invocation,  Next: sum invocation,  Up: Summarizing files

6.1 `wc': Print newline, word, and byte counts
==============================================

`wc' counts the number of bytes, characters, whitespace-separated
words, and newlines in each given FILE, or standard input if none are
given or for a FILE of `-'.  Synopsis:

     wc [OPTION]... [FILE]...

   `wc' prints one line of counts for each file, and if the file was
given as an argument, it prints the file name following the counts.  If
more than one FILE is given, `wc' prints a final line containing the
cumulative counts, with the file name `total'.  The counts are printed
in this order: newlines, words, characters, bytes, maximum line length.
Each count is printed right-justified in a field with at least one
space between fields so that the numbers and file names normally line
up nicely in columns.  The width of the count fields varies depending
on the inputs, so you should not depend on a particular field width.
However, as a GNU extension, if only one count is printed, it is
guaranteed to be printed without leading spaces.

   By default, `wc' prints three counts: the newline, words, and byte
counts.  Options can specify that only certain counts be printed.
Options do not undo others previously given, so

     wc --bytes --words

prints both the byte counts and the word counts.

   With the `--max-line-length' option, `wc' prints the length of the
longest line per file, and if there is more than one file it prints the
maximum (not the sum) of those lengths.  The line lengths here are
measured in screen columns, according to the current locale and
assuming tab positions in every 8th column.

   The program accepts the following options.  Also see *note Common
options::.

`-c'
`--bytes'
     Print only the byte counts.

`-m'
`--chars'
     Print only the character counts.

`-w'
`--words'
     Print only the word counts.

`-l'
`--lines'
     Print only the newline counts.

`-L'
`--max-line-length'
     Print only the maximum line lengths.

`--files0-from=FILE'
     Disallow processing files named on the command line, and instead
     process those named in file FILE; each name being terminated by a
     zero byte (ASCII NUL).  This is useful when the list of file names
     is so long that it may exceed a command line length limitation.
     In such cases, running `wc' via `xargs' is undesirable because it
     splits the list into pieces and makes `wc' print a total for each
     sublist rather than for the entire list.  One way to produce a
     list of ASCII NUL terminated file names is with GNU `find', using
     its `-print0' predicate.  If FILE is `-' then the ASCII NUL
     terminated file names are read from standard input.

     For example, to find the length of the longest line in any `.c' or
     `.h' file in the current hierarchy, do this:

          find . -name '*.[ch]' -print0 |
            wc -L --files0-from=- | tail -n1


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: sum invocation,  Next: cksum invocation,  Prev: wc invocation,  Up: Summarizing files

6.2 `sum': Print checksum and block counts
==========================================

`sum' computes a 16-bit checksum for each given FILE, or standard input
if none are given or for a FILE of `-'.  Synopsis:

     sum [OPTION]... [FILE]...

   `sum' prints the checksum for each FILE followed by the number of
blocks in the file (rounded up).  If more than one FILE is given, file
names are also printed (by default).  (With the `--sysv' option,
corresponding file names are printed when there is at least one file
argument.)

   By default, GNU `sum' computes checksums using an algorithm
compatible with BSD `sum' and prints file sizes in units of 1024-byte
blocks.

   The program accepts the following options.  Also see *note Common
options::.

`-r'
     Use the default (BSD compatible) algorithm.  This option is
     included for compatibility with the System V `sum'.  Unless `-s'
     was also given, it has no effect.

`-s'
`--sysv'
     Compute checksums using an algorithm compatible with System V
     `sum''s default, and print file sizes in units of 512-byte blocks.


   `sum' is provided for compatibility; the `cksum' program (see next
section) is preferable in new applications.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: cksum invocation,  Next: md5sum invocation,  Prev: sum invocation,  Up: Summarizing files

6.3 `cksum': Print CRC checksum and byte counts
===============================================

`cksum' computes a cyclic redundancy check (CRC) checksum for each
given FILE, or standard input if none are given or for a FILE of `-'.
Synopsis:

     cksum [OPTION]... [FILE]...

   `cksum' prints the CRC checksum for each file along with the number
of bytes in the file, and the file name unless no arguments were given.

   `cksum' is typically used to ensure that files transferred by
unreliable means (e.g., netnews) have not been corrupted, by comparing
the `cksum' output for the received files with the `cksum' output for
the original files (typically given in the distribution).

   The CRC algorithm is specified by the POSIX standard.  It is not
compatible with the BSD or System V `sum' algorithms (see the previous
section); it is more robust.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: md5sum invocation,  Next: sha1sum invocation,  Prev: cksum invocation,  Up: Summarizing files

6.4 `md5sum': Print or check MD5 digests
========================================

`md5sum' computes a 128-bit checksum (or "fingerprint" or
"message-digest") for each specified FILE.

   Note: The MD5 digest is more reliable than a simple CRC (provided by
the `cksum' command) for detecting accidental file corruption, as the
chances of accidentally having two files with identical MD5 are
vanishingly small.  However, it should not be considered truly secure
against malicious tampering: although finding a file with a given MD5
fingerprint, or modifying a file so as to retain its MD5 are considered
infeasible at the moment, it is known how to produce different files
with identical MD5 (a "collision"), something which can be a security
issue in certain contexts.  For more secure hashes, consider using
SHA-1 or SHA-2.  *Note sha1sum invocation::, and *note sha2 utilities::.

   If a FILE is specified as `-' or if no files are given `md5sum'
computes the checksum for the standard input.  `md5sum' can also
determine whether a file and checksum are consistent.  Synopsis:

     md5sum [OPTION]... [FILE]...

   For each FILE, `md5sum' outputs the MD5 checksum, a flag indicating
a binary or text input file, and the file name.  If FILE contains a
backslash or newline, the line is started with a backslash, and each
problematic character in the file name is escaped with a backslash,
making the output unambiguous even in the presence of arbitrary file
names.  If FILE is omitted or specified as `-', standard input is read.

   The program accepts the following options.  Also see *note Common
options::.

`-b'
`--binary'
     Treat each input file as binary, by reading it in binary mode and
     outputting a `*' flag.  This is the inverse of `--text'.  On
     systems like GNU that do not distinguish between binary and text
     files, this option merely flags each input file as binary: the MD5
     checksum is unaffected.  This option is the default on systems
     like MS-DOS that distinguish between binary and text files, except
     for reading standard input when standard input is a terminal.

`-c'
`--check'
     Read file names and checksum information (not data) from each FILE
     (or from stdin if no FILE was specified) and report whether the
     checksums match the contents of the named files.  The input to
     this mode of `md5sum' is usually the output of a prior,
     checksum-generating run of `md5sum'.  Each valid line of input
     consists of an MD5 checksum, a binary/text flag, and then a file
     name.  Binary files are marked with `*', text with ` '.  For each
     such line, `md5sum' reads the named file and computes its MD5
     checksum.  Then, if the computed message digest does not match the
     one on the line with the file name, the file is noted as having
     failed the test.  Otherwise, the file passes the test.  By
     default, for each valid line, one line is written to standard
     output indicating whether the named file passed the test.  After
     all checks have been performed, if there were any failures, a
     warning is issued to standard error.  Use the `--status' option to
     inhibit that output.  If any listed file cannot be opened or read,
     if any valid line has an MD5 checksum inconsistent with the
     associated file, or if no valid line is found, `md5sum' exits with
     nonzero status.  Otherwise, it exits successfully.

`--quiet'
     This option is useful only when verifying checksums.  When
     verifying checksums, don't generate an 'OK' message per
     successfully checked file.  Files that fail the verification are
     reported in the default one-line-per-file format.  If there is any
     checksum mismatch, print a warning summarizing the failures to
     standard error.

`--status'
     This option is useful only when verifying checksums.  When
     verifying checksums, don't generate the default one-line-per-file
     diagnostic and don't output the warning summarizing any failures.
     Failures to open or read a file still evoke individual diagnostics
     to standard error.  If all listed files are readable and are
     consistent with the associated MD5 checksums, exit successfully.
     Otherwise exit with a status code indicating there was a failure.

`-t'
`--text'
     Treat each input file as text, by reading it in text mode and
     outputting a ` ' flag.  This is the inverse of `--binary'.  This
     option is the default on systems like GNU that do not distinguish
     between binary and text files.  On other systems, it is the
     default for reading standard input when standard input is a
     terminal.

`-w'
`--warn'
     When verifying checksums, warn about improperly formatted MD5
     checksum lines.  This option is useful only if all but a few lines
     in the checked input are valid.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: sha1sum invocation,  Next: sha2 utilities,  Prev: md5sum invocation,  Up: Summarizing files

6.5 `sha1sum': Print or check SHA-1 digests
===========================================

`sha1sum' computes a 160-bit checksum for each specified FILE.  The
usage and options of this command are precisely the same as for
`md5sum'.  *Note md5sum invocation::.

   Note: The SHA-1 digest is more secure than MD5, and no collisions of
it are known (different files having the same fingerprint).  However,
it is known that they can be produced with considerable, but not
unreasonable, resources.  For this reason, it is generally considered
that SHA-1 should be gradually phased out in favor of the more secure
SHA-2 hash algorithms.  *Note sha2 utilities::.

File: coreutils.info,  Node: sha2 utilities,  Prev: sha1sum invocation,  Up: Summarizing files

6.6 sha2 utilities: Print or check SHA-2 digests
================================================

The commands `sha224sum', `sha256sum', `sha384sum' and `sha512sum'
compute checksums of various lengths (respectively 224, 256, 384 and
512 bits), collectively known as the SHA-2 hashes.  The usage and
options of these commands are precisely the same as for `md5sum'.
*Note md5sum invocation::.

   Note: The SHA384 and SHA512 digests are considerably slower to
compute, especially on 32-bit computers, than SHA224 or SHA256.

File: coreutils.info,  Node: Operating on sorted files,  Next: Operating on fields,  Prev: Summarizing files,  Up: Top

7 Operating on sorted files
***************************

These commands work with (or produce) sorted files.

* Menu:

* sort invocation::             Sort text files.
* shuf invocation::             Shuffle text files.
* uniq invocation::             Uniquify files.
* comm invocation::             Compare two sorted files line by line.
* ptx invocation::              Produce a permuted index of file contents.
* tsort invocation::            Topological sort.

File: coreutils.info,  Node: sort invocation,  Next: shuf invocation,  Up: Operating on sorted files

7.1 `sort': Sort text files
===========================

`sort' sorts, merges, or compares all the lines from the given files,
or standard input if none are given or for a FILE of `-'.  By default,
`sort' writes the results to standard output.  Synopsis:

     sort [OPTION]... [FILE]...

   `sort' has three modes of operation: sort (the default), merge, and
check for sortedness.  The following options change the operation mode:

`-c'
`--check'
`--check=diagnose-first'
     Check whether the given file is already sorted: if it is not all
     sorted, print a diagnostic containing the first out-of-order line
     and exit with a status of 1.  Otherwise, exit successfully.  At
     most one input file can be given.

`-C'
`--check=quiet'
`--check=silent'
     Exit successfully if the given file is already sorted, and exit
     with status 1 otherwise.  At most one input file can be given.
     This is like `-c', except it does not print a diagnostic.

`-m'
`--merge'
     Merge the given files by sorting them as a group.  Each input file
     must always be individually sorted.  It always works to sort
     instead of merge; merging is provided because it is faster, in the
     case where it works.


   A pair of lines is compared as follows: `sort' compares each pair of
fields, in the order specified on the command line, according to the
associated ordering options, until a difference is found or no fields
are left.  If no key fields are specified, `sort' uses a default key of
the entire line.  Finally, as a last resort when all keys compare
equal, `sort' compares entire lines as if no ordering options other
than `--reverse' (`-r') were specified.  The `--stable' (`-s') option
disables this "last-resort comparison" so that lines in which all
fields compare equal are left in their original relative order.  The
`--unique' (`-u') option also disables the last-resort comparison.

   Unless otherwise specified, all comparisons use the character
collating sequence specified by the `LC_COLLATE' locale.(1)

   GNU `sort' (as specified for all GNU utilities) has no limit on
input line length or restrictions on bytes allowed within lines.  In
addition, if the final byte of an input file is not a newline, GNU
`sort' silently supplies one.  A line's trailing newline is not part of
the line for comparison purposes.

   Exit status:

     0 if no error occurred
     1 if invoked with `-c' or `-C' and the input is not sorted
     2 if an error occurred

   If the environment variable `TMPDIR' is set, `sort' uses its value
as the directory for temporary files instead of `/tmp'.  The
`--temporary-directory' (`-T') option in turn overrides the environment
variable.

   The following options affect the ordering of output lines.  They may
be specified globally or as part of a specific key field.  If no key
fields are specified, global options apply to comparison of entire
lines; otherwise the global options are inherited by key fields that do
not specify any special options of their own.  In pre-POSIX versions of
`sort', global options affect only later key fields, so portable shell
scripts should specify global options first.

`-b'
`--ignore-leading-blanks'
     Ignore leading blanks when finding sort keys in each line.  By
     default a blank is a space or a tab, but the `LC_CTYPE' locale can
     change this.  Note blanks may be ignored by your locale's collating
     rules, but without this option they will be significant for
     character positions specified in keys with the `-k' option.

`-d'
`--dictionary-order'
     Sort in "phone directory" order: ignore all characters except
     letters, digits and blanks when sorting.  By default letters and
     digits are those of ASCII and a blank is a space or a tab, but the
     `LC_CTYPE' locale can change this.

`-f'
`--ignore-case'
     Fold lowercase characters into the equivalent uppercase characters
     when comparing so that, for example, `b' and `B' sort as equal.
     The `LC_CTYPE' locale determines character types.  When used with
     `--unique' those lower case equivalent lines are thrown away.
     (There is currently no way to throw away the upper case equivalent
     instead. (Any `--reverse' given would only affect the final
     result, after the throwing away.))

`-g'
`--general-numeric-sort'
`--sort=general-numeric'
     Sort numerically, using the standard C function `strtod' to convert
     a prefix of each line to a double-precision floating point number.
     This allows floating point numbers to be specified in scientific
     notation, like `1.0e-34' and `10e100'.  The `LC_NUMERIC' locale
     determines the decimal-point character.  Do not report overflow,
     underflow, or conversion errors.  Use the following collating
     sequence:

        * Lines that do not start with numbers (all considered to be
          equal).

        * NaNs ("Not a Number" values, in IEEE floating point
          arithmetic) in a consistent but machine-dependent order.

        * Minus infinity.

        * Finite numbers in ascending numeric order (with -0 and +0
          equal).

        * Plus infinity.

     Use this option only if there is no alternative; it is much slower
     than `--numeric-sort' (`-n') and it can lose information when
     converting to floating point.

`-h'
`--human-numeric-sort'
`--sort=human-numeric'
     Sort numerically, as per the `--numeric-sort' option below, and in
     addition handle IEC or SI suffixes like MiB, MB etc (*note Block
     size::).  Note a mixture of IEC and SI suffixes is not supported
     and will be flagged as an error.  Also the numbers must be
     abbreviated uniformly.  I.E. values with different precisions like
     6000K and 5M will be sorted incorrectly.

`-i'
`--ignore-nonprinting'
     Ignore nonprinting characters.  The `LC_CTYPE' locale determines
     character types.  This option has no effect if the stronger
     `--dictionary-order' (`-d') option is also given.

`-M'
`--month-sort'
`--sort=month'
     An initial string, consisting of any amount of blanks, followed by
     a month name abbreviation, is folded to UPPER case and compared in
     the order `JAN' < `FEB' < ... < `DEC'.  Invalid names compare low
     to valid names.  The `LC_TIME' locale category determines the
     month spellings.  By default a blank is a space or a tab, but the
     `LC_CTYPE' locale can change this.

`-n'
`--numeric-sort'
`--sort=numeric'
     Sort numerically.  The number begins each line and consists of
     optional blanks, an optional `-' sign, and zero or more digits
     possibly separated by thousands separators, optionally followed by
     a decimal-point character and zero or more digits.  An empty
     number is treated as `0'.  The `LC_NUMERIC' locale specifies the
     decimal-point character and thousands separator.  By default a
     blank is a space or a tab, but the `LC_CTYPE' locale can change
     this.

     Comparison is exact; there is no rounding error.

     Neither a leading `+' nor exponential notation is recognized.  To
     compare such strings numerically, use the `--general-numeric-sort'
     (`-g') option.

`-V'
`--version-sort'
     Sort by version name and number.  It behaves like a standard sort,
     except that each sequence of decimal digits is treated numerically
     as an index/version number.  (*Note Details about version sort::.)

`-r'
`--reverse'
     Reverse the result of comparison, so that lines with greater key
     values appear earlier in the output instead of later.

`-R'
`--random-sort'
`--sort=random'
     Sort by hashing the input keys and then sorting the hash values.
     Choose the hash function at random, ensuring that it is free of
     collisions so that differing keys have differing hash values.
     This is like a random permutation of the inputs (*note shuf
     invocation::), except that keys with the same value sort together.

     If multiple random sort fields are specified, the same random hash
     function is used for all fields.  To use different random hash
     functions for different fields, you can invoke `sort' more than
     once.

     The choice of hash function is affected by the `--random-source'
     option.


   Other options are:

`--compress-program=PROG'
     Compress any temporary files with the program PROG.

     With no arguments, PROG must compress standard input to standard
     output, and when given the `-d' option it must decompress standard
     input to standard output.

     Terminate with an error if PROG exits with nonzero status.

     White space and the backslash character should not appear in PROG;
     they are reserved for future use.

`--files0-from=FILE'
     Disallow processing files named on the command line, and instead
     process those named in file FILE; each name being terminated by a
     zero byte (ASCII NUL).  This is useful when the list of file names
     is so long that it may exceed a command line length limitation.
     In such cases, running `sort' via `xargs' is undesirable because
     it splits the list into pieces and makes `sort' print sorted
     output for each sublist rather than for the entire list.  One way
     to produce a list of ASCII NUL terminated file names is with GNU
     `find', using its `-print0' predicate.  If FILE is `-' then the
     ASCII NUL terminated file names are read from standard input.

`-k POS1[,POS2]'
`--key=POS1[,POS2]'
     Specify a sort field that consists of the part of the line between
     POS1 and POS2 (or the end of the line, if POS2 is omitted),
     _inclusive_.

     Each POS has the form `F[.C][OPTS]', where F is the number of the
     field to use, and C is the number of the first character from the
     beginning of the field.  Fields and character positions are
     numbered starting with 1; a character position of zero in POS2
     indicates the field's last character.  If `.C' is omitted from
     POS1, it defaults to 1 (the beginning of the field); if omitted
     from POS2, it defaults to 0 (the end of the field).  OPTS are
     ordering options, allowing individual keys to be sorted according
     to different rules; see below for details.  Keys can span multiple
     fields.

     Example:  To sort on the second field, use `--key=2,2' (`-k 2,2').
     See below for more notes on keys and more examples.

`--batch-size=NMERGE'
     Merge at most NMERGE inputs at once.

     When `sort' has to merge more than NMERGE inputs, it merges them
     in groups of NMERGE, saving the result in a temporary file, which
     is then used as an input in a subsequent merge.

     A large value of NMERGE may improve merge performance and decrease
     temporary storage utilization at the expense of increased memory
     usage and I/0.  Conversely a small value of NMERGE may reduce
     memory requirements and I/0 at the expense of temporary storage
     consumption and merge performance.

     The value of NMERGE must be at least 2.  The default value is
     currently 16, but this is implementation-dependent and may change
     in the future.

     The value of NMERGE may be bounded by a resource limit for open
     file descriptors.  The commands `ulimit -n' or `getconf OPEN_MAX'
     may display limits for your systems; these limits may be modified
     further if your program already has some files open, or if the
     operating system has other limits on the number of open files.  If
     the value of NMERGE exceeds the resource limit, `sort' silently
     uses a smaller value.

`-o OUTPUT-FILE'
`--output=OUTPUT-FILE'
     Write output to OUTPUT-FILE instead of standard output.  Normally,
     `sort' reads all input before opening OUTPUT-FILE, so you can
     safely sort a file in place by using commands like `sort -o F F'
     and `cat F | sort -o F'.  However, `sort' with `--merge' (`-m')
     can open the output file before reading all input, so a command
     like `cat F | sort -m -o F - G' is not safe as `sort' might start
     writing `F' before `cat' is done reading it.

     On newer systems, `-o' cannot appear after an input file if
     `POSIXLY_CORRECT' is set, e.g., `sort F -o F'.  Portable scripts
     should specify `-o OUTPUT-FILE' before any input files.

`--random-source=FILE'
     Use FILE as a source of random data used to determine which random
     hash function to use with the `-R' option.  *Note Random sources::.

`-s'
`--stable'
     Make `sort' stable by disabling its last-resort comparison.  This
     option has no effect if no fields or global ordering options other
     than `--reverse' (`-r') are specified.

`-S SIZE'
`--buffer-size=SIZE'
     Use a main-memory sort buffer of the given SIZE.  By default, SIZE
     is in units of 1024 bytes.  Appending `%' causes SIZE to be
     interpreted as a percentage of physical memory.  Appending `K'
     multiplies SIZE by 1024 (the default), `M' by 1,048,576, `G' by
     1,073,741,824, and so on for `T', `P', `E', `Z', and `Y'.
     Appending `b' causes SIZE to be interpreted as a byte count, with
     no multiplication.

     This option can improve the performance of `sort' by causing it to
     start with a larger or smaller sort buffer than the default.
     However, this option affects only the initial buffer size.  The
     buffer grows beyond SIZE if `sort' encounters input lines larger
     than SIZE.

`-t SEPARATOR'
`--field-separator=SEPARATOR'
     Use character SEPARATOR as the field separator when finding the
     sort keys in each line.  By default, fields are separated by the
     empty string between a non-blank character and a blank character.
     By default a blank is a space or a tab, but the `LC_CTYPE' locale
     can change this.

     That is, given the input line ` foo bar', `sort' breaks it into
     fields ` foo' and ` bar'.  The field separator is not considered
     to be part of either the field preceding or the field following,
     so with `sort -t " "' the same input line has three fields: an
     empty field, `foo', and `bar'.  However, fields that extend to the
     end of the line, as `-k 2', or fields consisting of a range, as
     `-k 2,3', retain the field separators present between the
     endpoints of the range.

     To specify ASCII NUL as the field separator, use the two-character
     string `\0', e.g., `sort -t '\0''.

`-T TEMPDIR'
`--temporary-directory=TEMPDIR'
     Use directory TEMPDIR to store temporary files, overriding the
     `TMPDIR' environment variable.  If this option is given more than
     once, temporary files are stored in all the directories given.  If
     you have a large sort or merge that is I/O-bound, you can often
     improve performance by using this option to specify directories on
     different disks and controllers.

`-u'
`--unique'
     Normally, output only the first of a sequence of lines that compare
     equal.  For the `--check' (`-c' or `-C') option, check that no
     pair of consecutive lines compares equal.

     This option also disables the default last-resort comparison.

     The commands `sort -u' and `sort | uniq' are equivalent, but this
     equivalence does not extend to arbitrary `sort' options.  For
     example, `sort -n -u' inspects only the value of the initial
     numeric string when checking for uniqueness, whereas `sort -n |
     uniq' inspects the entire line.  *Note uniq invocation::.

`-z'
`--zero-terminated'
     Delimit items with a zero byte rather than a newline (ASCII LF).
     I.E. treat input as items separated by ASCII NUL and terminate
     output items with ASCII NUL.  This option can be useful in
     conjunction with `perl -0' or `find -print0' and `xargs -0' which
     do the same in order to reliably handle arbitrary file names (even
     those containing blanks or other special characters).


   Historical (BSD and System V) implementations of `sort' have
differed in their interpretation of some options, particularly `-b',
`-f', and `-n'.  GNU sort follows the POSIX behavior, which is usually
(but not always!) like the System V behavior.  According to POSIX, `-n'
no longer implies `-b'.  For consistency, `-M' has been changed in the
same way.  This may affect the meaning of character positions in field
specifications in obscure cases.  The only fix is to add an explicit
`-b'.

   A position in a sort field specified with `-k' may have any of the
option letters `MbdfghinRrV' appended to it, in which case no global
ordering options are inherited by that particular field.  The `-b'
option may be independently attached to either or both of the start and
end positions of a field specification, and if it is inherited from the
global options it will be attached to both.  If input lines can contain
leading or adjacent blanks and `-t' is not used, then `-k' is typically
combined with `-b' or an option that implicitly ignores leading blanks
(`MghnV') as otherwise the varying numbers of leading blanks in fields
can cause confusing results.

   If the start position in a sort field specifier falls after the end
of the line or after the end field, the field is empty.  If the `-b'
option was specified, the `.C' part of a field specification is counted
from the first nonblank character of the field.

   On older systems, `sort' supports an obsolete origin-zero syntax
`+POS1 [-POS2]' for specifying sort keys.  This obsolete behavior can
be enabled or disabled with the `_POSIX2_VERSION' environment variable
(*note Standards conformance::); it can also be enabled when
`POSIXLY_CORRECT' is not set by using the obsolete syntax with `-POS2'
present.

   Scripts intended for use on standard hosts should avoid obsolete
syntax and should use `-k' instead.  For example, avoid `sort +2',
since it might be interpreted as either `sort ./+2' or `sort -k 3'.  If
your script must also run on hosts that support only the obsolete
syntax, it can use a test like `if sort -k 1 </dev/null >/dev/null
2>&1; then ...' to decide which syntax to use.

   Here are some examples to illustrate various combinations of options.

   * Sort in descending (reverse) numeric order.

          sort -n -r

   * Sort alphabetically, omitting the first and second fields and the
     blanks at the start of the third field.  This uses a single key
     composed of the characters beginning at the start of the first
     nonblank character in field three and extending to the end of each
     line.

          sort -k 3b

   * Sort numerically on the second field and resolve ties by sorting
     alphabetically on the third and fourth characters of field five.
     Use `:' as the field delimiter.

          sort -t : -k 2,2n -k 5.3,5.4

     Note that if you had written `-k 2n' instead of `-k 2,2n' `sort'
     would have used all characters beginning in the second field and
     extending to the end of the line as the primary _numeric_ key.
     For the large majority of applications, treating keys spanning
     more than one field as numeric will not do what you expect.

     Also note that the `n' modifier was applied to the field-end
     specifier for the first key.  It would have been equivalent to
     specify `-k 2n,2' or `-k 2n,2n'.  All modifiers except `b' apply
     to the associated _field_, regardless of whether the modifier
     character is attached to the field-start and/or the field-end part
     of the key specifier.

   * Sort the password file on the fifth field and ignore any leading
     blanks.  Sort lines with equal values in field five on the numeric
     user ID in field three.  Fields are separated by `:'.

          sort -t : -k 5b,5 -k 3,3n /etc/passwd
          sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
          sort -t : -b -k 5,5 -k 3,3n /etc/passwd

     These three commands have equivalent effect.  The first specifies
     that the first key's start position ignores leading blanks and the
     second key is sorted numerically.  The other two commands rely on
     global options being inherited by sort keys that lack modifiers.
     The inheritance works in this case because `-k 5b,5b' and `-k
     5b,5' are equivalent, as the location of a field-end lacking a `.C'
     character position is not affected by whether initial blanks are
     skipped.

   * Sort a set of log files, primarily by IPv4 address and secondarily
     by time stamp.  If two lines' primary and secondary keys are
     identical, output the lines in the same order that they were
     input.  The log files contain lines that look like this:

          4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
          211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2

     Fields are separated by exactly one space.  Sort IPv4 addresses
     lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
     because 61 is less than 129.

          sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
          sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n

     This example cannot be done with a single `sort' invocation, since
     IPv4 address components are separated by `.' while dates come just
     after a space.  So it is broken down into two invocations of
     `sort': the first sorts by time stamp and the second by IPv4
     address.  The time stamp is sorted by year, then month, then day,
     and finally by hour-minute-second field, using `-k' to isolate each
     field.  Except for hour-minute-second there's no need to specify
     the end of each key field, since the `n' and `M' modifiers sort
     based on leading prefixes that cannot cross field boundaries.  The
     IPv4 addresses are sorted lexicographically.  The second sort uses
     `-s' so that ties in the primary key are broken by the secondary
     key; the first sort uses `-s' so that the combination of the two
     sorts is stable.

   * Generate a tags file in case-insensitive sorted order.

          find src -type f -print0 | sort -z -f | xargs -0 etags --append

     The use of `-print0', `-z', and `-0' in this case means that file
     names that contain blanks or other special characters are not
     broken up by the sort operation.

   * Use the common DSU (Decorate Sort Undecorate) idiom to sort lines
     according to their length.

          awk '{print length, $0}' /etc/passwd | sort -n | cut -f2- -d' '

     In general this technique can be used to sort data that the `sort'
     command does not support, or is inefficient at, sorting directly.

   * Shuffle a list of directories, but preserve the order of files
     within each directory.  For instance, one could use this to
     generate a music playlist in which albums are shuffled but the
     songs of each album are played in order.

          ls */* | sort -t / -k 1,1R -k 2,2


   ---------- Footnotes ----------

   (1) If you use a non-POSIX locale (e.g., by setting `LC_ALL' to
`en_US'), then `sort' may produce output that is sorted differently
than you're accustomed to.  In that case, set the `LC_ALL' environment
variable to `C'.  Note that setting only `LC_COLLATE' has two problems.
First, it is ineffective if `LC_ALL' is also set.  Second, it has
undefined behavior if `LC_CTYPE' (or `LANG', if `LC_CTYPE' is unset) is
set to an incompatible value.  For example, you get undefined behavior
if `LC_CTYPE' is `ja_JP.PCK' but `LC_COLLATE' is `en_US.UTF-8'.

File: coreutils.info,  Node: shuf invocation,  Next: uniq invocation,  Prev: sort invocation,  Up: Operating on sorted files

7.2 `shuf': Shuffling text
==========================

`shuf' shuffles its input by outputting a random permutation of its
input lines.  Each output permutation is equally likely.  Synopses:

     shuf [OPTION]... [FILE]
     shuf -e [OPTION]... [ARG]...
     shuf -i LO-HI [OPTION]...

   `shuf' has three modes of operation that affect where it obtains its
input lines.  By default, it reads lines from standard input.  The
following options change the operation mode:

`-e'
`--echo'
     Treat each command-line operand as an input line.

`-i LO-HI'
`--input-range=LO-HI'
     Act as if input came from a file containing the range of unsigned
     decimal integers LO...HI, one per line.


   `shuf''s other options can affect its behavior in all operation
modes:

`-n LINES'
`--head-count=COUNT'
     Output at most COUNT lines.  By default, all input lines are
     output.

`-o OUTPUT-FILE'
`--output=OUTPUT-FILE'
     Write output to OUTPUT-FILE instead of standard output.  `shuf'
     reads all input before opening OUTPUT-FILE, so you can safely
     shuffle a file in place by using commands like `shuf -o F <F' and
     `cat F | shuf -o F'.

`--random-source=FILE'
     Use FILE as a source of random data used to determine which
     permutation to generate.  *Note Random sources::.

`-z'
`--zero-terminated'
     Delimit items with a zero byte rather than a newline (ASCII LF).
     I.E. treat input as items separated by ASCII NUL and terminate
     output items with ASCII NUL.  This option can be useful in
     conjunction with `perl -0' or `find -print0' and `xargs -0' which
     do the same in order to reliably handle arbitrary file names (even
     those containing blanks or other special characters).


   For example:

     shuf <<EOF
     A man,
     a plan,
     a canal:
     Panama!
     EOF

might produce the output

     Panama!
     A man,
     a canal:
     a plan,

Similarly, the command:

     shuf -e clubs hearts diamonds spades

might output:

     clubs
     diamonds
     spades
     hearts

and the command `shuf -i 1-4' might output:

     4
     2
     1
     3

These examples all have four input lines, so `shuf' might produce any
of the twenty-four possible permutations of the input.  In general, if
there are N input lines, there are N! (i.e., N factorial, or N * (N -
1) * ... * 1) possible output permutations.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: uniq invocation,  Next: comm invocation,  Prev: shuf invocation,  Up: Operating on sorted files

7.3 `uniq': Uniquify files
==========================

`uniq' writes the unique lines in the given `input', or standard input
if nothing is given or for an INPUT name of `-'.  Synopsis:

     uniq [OPTION]... [INPUT [OUTPUT]]

   By default, `uniq' prints its input lines, except that it discards
all but the first of adjacent repeated lines, so that no output lines
are repeated.  Optionally, it can instead discard lines that are not
repeated, or all repeated lines.

   The input need not be sorted, but repeated input lines are detected
only if they are adjacent.  If you want to discard non-adjacent
duplicate lines, perhaps you want to use `sort -u'.  *Note sort
invocation::.

   Comparisons honor the rules specified by the `LC_COLLATE' locale
category.

   If no OUTPUT file is specified, `uniq' writes to standard output.

   The program accepts the following options.  Also see *note Common
options::.

`-f N'
`--skip-fields=N'
     Skip N fields on each line before checking for uniqueness.  Use a
     null string for comparison if a line has fewer than N fields.
     Fields are sequences of non-space non-tab characters that are
     separated from each other by at least one space or tab.

     For compatibility `uniq' supports an obsolete option syntax `-N'.
     New scripts should use `-f N' instead.

`-s N'
`--skip-chars=N'
     Skip N characters before checking for uniqueness.  Use a null
     string for comparison if a line has fewer than N characters.  If
     you use both the field and character skipping options, fields are
     skipped over first.

     On older systems, `uniq' supports an obsolete option syntax `+N'.
     This obsolete behavior can be enabled or disabled with the
     `_POSIX2_VERSION' environment variable (*note Standards
     conformance::), but portable scripts should avoid commands whose
     behavior depends on this variable.  For example, use `uniq ./+10'
     or `uniq -s 10' rather than the ambiguous `uniq +10'.

`-c'
`--count'
     Print the number of times each line occurred along with the line.

`-i'
`--ignore-case'
     Ignore differences in case when comparing lines.

`-d'
`--repeated'
     Discard lines that are not repeated.  When used by itself, this
     option causes `uniq' to print the first copy of each repeated line,
     and nothing else.

`-D'
`--all-repeated[=DELIMIT-METHOD]'
     Do not discard the second and subsequent repeated input lines, but
     discard lines that are not repeated.  This option is useful mainly
     in conjunction with other options e.g., to ignore case or to
     compare only selected fields.  The optional DELIMIT-METHOD tells
     how to delimit groups of repeated lines, and must be one of the
     following:

    `none'
          Do not delimit groups of repeated lines.  This is equivalent
          to `--all-repeated' (`-D').

    `prepend'
          Output a newline before each group of repeated lines.  With
          `--zero-terminated' (`-z'), use a zero byte (ASCII NUL)
          instead of a newline.

    `separate'
          Separate groups of repeated lines with a single newline.
          With `--zero-terminated' (`-z'), use a zero byte (ASCII NUL)
          instead of a newline.  This is the same as using `prepend',
          except that no delimiter is inserted before the first group,
          and hence may be better suited for output direct to users.

     Note that when groups are delimited and the input stream contains
     two or more consecutive blank lines, then the output is ambiguous.
     To avoid that, filter the input through `tr -s '\n'' to replace
     each sequence of consecutive newlines with a single newline.

     This is a GNU extension.

`-u'
`--unique'
     Discard the first repeated line.  When used by itself, this option
     causes `uniq' to print unique lines, and nothing else.

`-w N'
`--check-chars=N'
     Compare at most N characters on each line (after skipping any
     specified fields and characters).  By default the entire rest of
     the lines are compared.

`-z'
`--zero-terminated'
     Delimit items with a zero byte rather than a newline (ASCII LF).
     I.E. treat input as items separated by ASCII NUL and terminate
     output items with ASCII NUL.  This option can be useful in
     conjunction with `perl -0' or `find -print0' and `xargs -0' which
     do the same in order to reliably handle arbitrary file names (even
     those containing blanks or other special characters).


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: comm invocation,  Next: ptx invocation,  Prev: uniq invocation,  Up: Operating on sorted files

7.4 `comm': Compare two sorted files line by line
=================================================

`comm' writes to standard output lines that are common, and lines that
are unique, to two input files; a file name of `-' means standard
input.  Synopsis:

     comm [OPTION]... FILE1 FILE2

   Before `comm' can be used, the input files must be sorted using the
collating sequence specified by the `LC_COLLATE' locale.  If an input
file ends in a non-newline character, a newline is silently appended.
The `sort' command with no options always outputs a file that is
suitable input to `comm'.

   With no options, `comm' produces three-column output.  Column one
contains lines unique to FILE1, column two contains lines unique to
FILE2, and column three contains lines common to both files.  Columns
are separated by a single TAB character.

   The options `-1', `-2', and `-3' suppress printing of the
corresponding columns (and separators).  Also see *note Common
options::.

   Unlike some other comparison utilities, `comm' has an exit status
that does not depend on the result of the comparison.  Upon normal
completion `comm' produces an exit code of zero.  If there is an error
it exits with nonzero status.

   If the `--check-order' option is given, unsorted inputs will cause a
fatal error message.  If the option `--nocheck-order' is given,
unsorted inputs will never cause an error message.  If neither of these
options is given, wrongly sorted inputs are diagnosed only if an input
file is found to contain unpairable lines.  If an input file is
diagnosed as being unsorted, the `comm' command will exit with a
nonzero status (and the output should not be used).

   Forcing `comm' to process wrongly sorted input files containing
unpairable lines by specifying `--nocheck-order' is not guaranteed to
produce any particular output.  The output will probably not correspond
with whatever you hoped it would be.

`--check-order'
     Fail with an error message if either input file is wrongly ordered.

`--nocheck-order'
     Do not check that both input files are in sorted order.

     Other options are:

`--output-delimiter=STR'
     Print STR between adjacent output columns, rather than the default
     of a single TAB character.

     The delimiter STR may not be empty.


File: coreutils.info,  Node: ptx invocation,  Next: tsort invocation,  Prev: comm invocation,  Up: Operating on sorted files

7.5 `ptx': Produce permuted indexes
===================================

`ptx' reads a text file and essentially produces a permuted index, with
each keyword in its context.  The calling sketch is either one of:

     ptx [OPTION ...] [FILE ...]
     ptx -G [OPTION ...] [INPUT [OUTPUT]]

   The `-G' (or its equivalent: `--traditional') option disables all
GNU extensions and reverts to traditional mode, thus introducing some
limitations and changing several of the program's default option values.
When `-G' is not specified, GNU extensions are always enabled.  GNU
extensions to `ptx' are documented wherever appropriate in this
document.  For the full list, see *Note Compatibility in ptx::.

   Individual options are explained in the following sections.

   When GNU extensions are enabled, there may be zero, one or several
FILEs after the options.  If there is no FILE, the program reads the
standard input.  If there is one or several FILEs, they give the name
of input files which are all read in turn, as if all the input files
were concatenated.  However, there is a full contextual break between
each file and, when automatic referencing is requested, file names and
line numbers refer to individual text input files.  In all cases, the
program outputs the permuted index to the standard output.

   When GNU extensions are _not_ enabled, that is, when the program
operates in traditional mode, there may be zero, one or two parameters
besides the options.  If there are no parameters, the program reads the
standard input and outputs the permuted index to the standard output.
If there is only one parameter, it names the text INPUT to be read
instead of the standard input.  If two parameters are given, they give
respectively the name of the INPUT file to read and the name of the
OUTPUT file to produce.  _Be very careful_ to note that, in this case,
the contents of file given by the second parameter is destroyed.  This
behavior is dictated by System V `ptx' compatibility; GNU Standards
normally discourage output parameters not introduced by an option.

   Note that for _any_ file named as the value of an option or as an
input text file, a single dash `-' may be used, in which case standard
input is assumed.  However, it would not make sense to use this
convention more than once per program invocation.

* Menu:

* General options in ptx::      Options which affect general program behavior.
* Charset selection in ptx::    Underlying character set considerations.
* Input processing in ptx::     Input fields, contexts, and keyword selection.
* Output formatting in ptx::    Types of output format, and sizing the fields.
* Compatibility in ptx::

File: coreutils.info,  Node: General options in ptx,  Next: Charset selection in ptx,  Up: ptx invocation

7.5.1 General options
---------------------

`-G'
`--traditional'
     As already explained, this option disables all GNU extensions to
     `ptx' and switches to traditional mode.

`--help'
     Print a short help on standard output, then exit without further
     processing.

`--version'
     Print the program version on standard output, then exit without
     further processing.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: Charset selection in ptx,  Next: Input processing in ptx,  Prev: General options in ptx,  Up: ptx invocation

7.5.2 Charset selection
-----------------------

As it is set up now, the program assumes that the input file is coded
using 8-bit ISO 8859-1 code, also known as Latin-1 character set,
_unless_ it is compiled for MS-DOS, in which case it uses the character
set of the IBM-PC.  (GNU `ptx' is not known to work on smaller MS-DOS
machines anymore.)  Compared to 7-bit ASCII, the set of characters
which are letters is different; this alters the behavior of regular
expression matching.  Thus, the default regular expression for a
keyword allows foreign or diacriticized letters.  Keyword sorting,
however, is still crude; it obeys the underlying character set ordering
quite blindly.

`-f'
`--ignore-case'
     Fold lower case letters to upper case for sorting.


File: coreutils.info,  Node: Input processing in ptx,  Next: Output formatting in ptx,  Prev: Charset selection in ptx,  Up: ptx invocation

7.5.3 Word selection and input processing
-----------------------------------------

`-b FILE'
`--break-file=FILE'
     This option provides an alternative (to `-W') method of describing
     which characters make up words.  It introduces the name of a file
     which contains a list of characters which can_not_ be part of one
     word; this file is called the "Break file".  Any character which
     is not part of the Break file is a word constituent.  If both
     options `-b' and `-W' are specified, then `-W' has precedence and
     `-b' is ignored.

     When GNU extensions are enabled, the only way to avoid newline as a
     break character is to write all the break characters in the file
     with no newline at all, not even at the end of the file.  When GNU
     extensions are disabled, spaces, tabs and newlines are always
     considered as break characters even if not included in the Break
     file.

`-i FILE'
`--ignore-file=FILE'
     The file associated with this option contains a list of words
     which will never be taken as keywords in concordance output.  It
     is called the "Ignore file".  The file contains exactly one word
     in each line; the end of line separation of words is not subject
     to the value of the `-S' option.

`-o FILE'
`--only-file=FILE'
     The file associated with this option contains a list of words
     which will be retained in concordance output; any word not
     mentioned in this file is ignored.  The file is called the "Only
     file".  The file contains exactly one word in each line; the end
     of line separation of words is not subject to the value of the
     `-S' option.

     There is no default for the Only file.  When both an Only file and
     an Ignore file are specified, a word is considered a keyword only
     if it is listed in the Only file and not in the Ignore file.

`-r'
`--references'
     On each input line, the leading sequence of non-white space
     characters will be taken to be a reference that has the purpose of
     identifying this input line in the resulting permuted index.  For
     more information about reference production, see *Note Output
     formatting in ptx::.  Using this option changes the default value
     for option `-S'.

     Using this option, the program does not try very hard to remove
     references from contexts in output, but it succeeds in doing so
     _when_ the context ends exactly at the newline.  If option `-r' is
     used with `-S' default value, or when GNU extensions are disabled,
     this condition is always met and references are completely
     excluded from the output contexts.

`-S REGEXP'
`--sentence-regexp=REGEXP'
     This option selects which regular expression will describe the end
     of a line or the end of a sentence.  In fact, this regular
     expression is not the only distinction between end of lines or end
     of sentences, and input line boundaries have no special
     significance outside this option.  By default, when GNU extensions
     are enabled and if `-r' option is not used, end of sentences are
     used.  In this case, this REGEX is imported from GNU Emacs:

          [.?!][]\"')}]*\\($\\|\t\\|  \\)[ \t\n]*

     Whenever GNU extensions are disabled or if `-r' option is used, end
     of lines are used; in this case, the default REGEXP is just:

          \n

     Using an empty REGEXP is equivalent to completely disabling end of
     line or end of sentence recognition.  In this case, the whole file
     is considered to be a single big line or sentence.  The user might
     want to disallow all truncation flag generation as well, through
     option `-F ""'.  *Note Syntax of Regular Expressions:
     (emacs)Regexps.

     When the keywords happen to be near the beginning of the input
     line or sentence, this often creates an unused area at the
     beginning of the output context line; when the keywords happen to
     be near the end of the input line or sentence, this often creates
     an unused area at the end of the output context line.  The program
     tries to fill those unused areas by wrapping around context in
     them; the tail of the input line or sentence is used to fill the
     unused area on the left of the output line; the head of the input
     line or sentence is used to fill the unused area on the right of
     the output line.

     As a matter of convenience to the user, many usual backslashed
     escape sequences from the C language are recognized and converted
     to the corresponding characters by `ptx' itself.

`-W REGEXP'
`--word-regexp=REGEXP'
     This option selects which regular expression will describe each
     keyword.  By default, if GNU extensions are enabled, a word is a
     sequence of letters; the REGEXP used is `\w+'.  When GNU
     extensions are disabled, a word is by default anything which ends
     with a space, a tab or a newline; the REGEXP used is `[^ \t\n]+'.

     An empty REGEXP is equivalent to not using this option.  *Note
     Syntax of Regular Expressions: (emacs)Regexps.

     As a matter of convenience to the user, many usual backslashed
     escape sequences, as found in the C language, are recognized and
     converted to the corresponding characters by `ptx' itself.


File: coreutils.info,  Node: Output formatting in ptx,  Next: Compatibility in ptx,  Prev: Input processing in ptx,  Up: ptx invocation

7.5.4 Output formatting
-----------------------

Output format is mainly controlled by the `-O' and `-T' options
described in the table below.  When neither `-O' nor `-T' are selected,
and if GNU extensions are enabled, the program chooses an output format
suitable for a dumb terminal.  Each keyword occurrence is output to the
center of one line, surrounded by its left and right contexts.  Each
field is properly justified, so the concordance output can be readily
observed.  As a special feature, if automatic references are selected
by option `-A' and are output before the left context, that is, if
option `-R' is _not_ selected, then a colon is added after the
reference; this nicely interfaces with GNU Emacs `next-error'
processing.  In this default output format, each white space character,
like newline and tab, is merely changed to exactly one space, with no
special attempt to compress consecutive spaces.  This might change in
the future.  Except for those white space characters, every other
character of the underlying set of 256 characters is transmitted
verbatim.

   Output format is further controlled by the following options.

`-g NUMBER'
`--gap-size=NUMBER'
     Select the size of the minimum white space gap between the fields
     on the output line.

`-w NUMBER'
`--width=NUMBER'
     Select the maximum output width of each final line.  If references
     are used, they are included or excluded from the maximum output
     width depending on the value of option `-R'.  If this option is not
     selected, that is, when references are output before the left
     context, the maximum output width takes into account the maximum
     length of all references.  If this option is selected, that is,
     when references are output after the right context, the maximum
     output width does not take into account the space taken by
     references, nor the gap that precedes them.

`-A'
`--auto-reference'
     Select automatic references.  Each input line will have an
     automatic reference made up of the file name and the line ordinal,
     with a single colon between them.  However, the file name will be
     empty when standard input is being read.  If both `-A' and `-r'
     are selected, then the input reference is still read and skipped,
     but the automatic reference is used at output time, overriding the
     input reference.

`-R'
`--right-side-refs'
     In the default output format, when option `-R' is not used, any
     references produced by the effect of options `-r' or `-A' are
     placed to the far right of output lines, after the right context.
     With default output format, when the `-R' option is specified,
     references are rather placed at the beginning of each output line,
     before the left context.  For any other output format, option `-R'
     is ignored, with one exception:  with `-R' the width of references
     is _not_ taken into account in total output width given by `-w'.

     This option is automatically selected whenever GNU extensions are
     disabled.

`-F STRING'
`--flac-truncation=STRING'
     This option will request that any truncation in the output be
     reported using the string STRING.  Most output fields
     theoretically extend towards the beginning or the end of the
     current line, or current sentence, as selected with option `-S'.
     But there is a maximum allowed output line width, changeable
     through option `-w', which is further divided into space for
     various output fields.  When a field has to be truncated because
     it cannot extend beyond the beginning or the end of the current
     line to fit in, then a truncation occurs.  By default, the string
     used is a single slash, as in `-F /'.

     STRING may have more than one character, as in `-F ...'.  Also, in
     the particular case when STRING is empty (`-F ""'), truncation
     flagging is disabled, and no truncation marks are appended in this
     case.

     As a matter of convenience to the user, many usual backslashed
     escape sequences, as found in the C language, are recognized and
     converted to the corresponding characters by `ptx' itself.

`-M STRING'
`--macro-name=STRING'
     Select another STRING to be used instead of `xx', while generating
     output suitable for `nroff', `troff' or TeX.

`-O'
`--format=roff'
     Choose an output format suitable for `nroff' or `troff'
     processing.  Each output line will look like:

          .xx "TAIL" "BEFORE" "KEYWORD_AND_AFTER" "HEAD" "REF"

     so it will be possible to write a `.xx' roff macro to take care of
     the output typesetting.  This is the default output format when GNU
     extensions are disabled.  Option `-M' can be used to change `xx'
     to another macro name.

     In this output format, each non-graphical character, like newline
     and tab, is merely changed to exactly one space, with no special
     attempt to compress consecutive spaces.  Each quote character: `"'
     is doubled so it will be correctly processed by `nroff' or `troff'.

`-T'
`--format=tex'
     Choose an output format suitable for TeX processing.  Each output
     line will look like:

          \xx {TAIL}{BEFORE}{KEYWORD}{AFTER}{HEAD}{REF}

     so it will be possible to write a `\xx' definition to take care of
     the output typesetting.  Note that when references are not being
     produced, that is, neither option `-A' nor option `-r' is
     selected, the last parameter of each `\xx' call is inhibited.
     Option `-M' can be used to change `xx' to another macro name.

     In this output format, some special characters, like `$', `%',
     `&', `#' and `_' are automatically protected with a backslash.
     Curly brackets `{', `}' are protected with a backslash and a pair
     of dollar signs (to force mathematical mode).  The backslash
     itself produces the sequence `\backslash{}'.  Circumflex and tilde
     diacritical marks produce the sequence `^\{ }' and `~\{ }'
     respectively.  Other diacriticized characters of the underlying
     character set produce an appropriate TeX sequence as far as
     possible.  The other non-graphical characters, like newline and
     tab, and all other characters which are not part of ASCII, are
     merely changed to exactly one space, with no special attempt to
     compress consecutive spaces.  Let me know how to improve this
     special character processing for TeX.


File: coreutils.info,  Node: Compatibility in ptx,  Prev: Output formatting in ptx,  Up: ptx invocation

7.5.5 The GNU extensions to `ptx'
---------------------------------

This version of `ptx' contains a few features which do not exist in
System V `ptx'.  These extra features are suppressed by using the `-G'
command line option, unless overridden by other command line options.
Some GNU extensions cannot be recovered by overriding, so the simple
rule is to avoid `-G' if you care about GNU extensions.  Here are the
differences between this program and System V `ptx'.

   * This program can read many input files at once, it always writes
     the resulting concordance on standard output.  On the other hand,
     System V `ptx' reads only one file and sends the result to
     standard output or, if a second FILE parameter is given on the
     command, to that FILE.

     Having output parameters not introduced by options is a dangerous
     practice which GNU avoids as far as possible.  So, for using `ptx'
     portably between GNU and System V, you should always use it with a
     single input file, and always expect the result on standard
     output.  You might also want to automatically configure in a `-G'
     option to `ptx' calls in products using `ptx', if the configurator
     finds that the installed `ptx' accepts `-G'.

   * The only options available in System V `ptx' are options `-b',
     `-f', `-g', `-i', `-o', `-r', `-t' and `-w'.  All other options
     are GNU extensions and are not repeated in this enumeration.
     Moreover, some options have a slightly different meaning when GNU
     extensions are enabled, as explained below.

   * By default, concordance output is not formatted for `troff' or
     `nroff'.  It is rather formatted for a dumb terminal.  `troff' or
     `nroff' output may still be selected through option `-O'.

   * Unless `-R' option is used, the maximum reference width is
     subtracted from the total output line width.  With GNU extensions
     disabled, width of references is not taken into account in the
     output line width computations.

   * All 256 bytes, even ASCII NUL bytes, are always read and processed
     from input file with no adverse effect, even if GNU extensions are
     disabled. However, System V `ptx' does not accept 8-bit characters,
     a few control characters are rejected, and the tilde `~' is also
     rejected.

   * Input line length is only limited by available memory, even if GNU
     extensions are disabled.  However, System V `ptx' processes only
     the first 200 characters in each line.

   * The break (non-word) characters default to be every character
     except all letters of the underlying character set, diacriticized
     or not.  When GNU extensions are disabled, the break characters
     default to space, tab and newline only.

   * The program makes better use of output line width.  If GNU
     extensions are disabled, the program rather tries to imitate
     System V `ptx', but still, there are some slight disposition
     glitches this program does not completely reproduce.

   * The user can specify both an Ignore file and an Only file.  This
     is not allowed with System V `ptx'.


File: coreutils.info,  Node: tsort invocation,  Prev: ptx invocation,  Up: Operating on sorted files

7.6 `tsort': Topological sort
=============================

`tsort' performs a topological sort on the given FILE, or standard
input if no input file is given or for a FILE of `-'.  For more details
and some history, see *note tsort background::.  Synopsis:

     tsort [OPTION] [FILE]

   `tsort' reads its input as pairs of strings, separated by blanks,
indicating a partial ordering.  The output is a total ordering that
corresponds to the given partial ordering.

   For example

     tsort <<EOF
     a b c
     d
     e f
     b c d e
     EOF

will produce the output

     a
     b
     c
     d
     e
     f

   Consider a more realistic example.  You have a large set of
functions all in one file, and they may all be declared static except
one.  Currently that one (say `main') is the first function defined in
the file, and the ones it calls directly follow it, followed by those
they call, etc.  Let's say that you are determined to take advantage of
prototypes, so you have to choose between declaring all of those
functions (which means duplicating a lot of information from the
definitions) and rearranging the functions so that as many as possible
are defined before they are used.  One way to automate the latter
process is to get a list for each function of the functions it calls
directly.  Many programs can generate such lists.  They describe a call
graph.  Consider the following list, in which a given line indicates
that the function on the left calls the one on the right directly.

     main parse_options
     main tail_file
     main tail_forever
     tail_file pretty_name
     tail_file write_header
     tail_file tail
     tail_forever recheck
     tail_forever pretty_name
     tail_forever write_header
     tail_forever dump_remainder
     tail tail_lines
     tail tail_bytes
     tail_lines start_lines
     tail_lines dump_remainder
     tail_lines file_lines
     tail_lines pipe_lines
     tail_bytes xlseek
     tail_bytes start_bytes
     tail_bytes dump_remainder
     tail_bytes pipe_bytes
     file_lines dump_remainder
     recheck pretty_name

   then you can use `tsort' to produce an ordering of those functions
that satisfies your requirement.

     example$ tsort call-graph | tac
     dump_remainder
     start_lines
     file_lines
     pipe_lines
     xlseek
     start_bytes
     pipe_bytes
     tail_lines
     tail_bytes
     pretty_name
     write_header
     tail
     recheck
     parse_options
     tail_file
     tail_forever
     main

   `tsort' detects any cycles in the input and writes the first cycle
encountered to standard error.

   Note that for a given partial ordering, generally there is no unique
total ordering.  In the context of the call graph above, the function
`parse_options' may be placed anywhere in the list as long as it
precedes `main'.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

* Menu:

* tsort background::            Where tsort came from.

File: coreutils.info,  Node: tsort background,  Up: tsort invocation

7.6.1 `tsort': Background
-------------------------

`tsort' exists because very early versions of the Unix linker processed
an archive file exactly once, and in order.  As `ld' read each object
in the archive, it decided whether it was needed in the program based on
whether it defined any symbols which were undefined at that point in
the link.

   This meant that dependencies within the archive had to be handled
specially.  For example, `scanf' probably calls `read'.  That means
that in a single pass through an archive, it was important for `scanf.o'
to appear before read.o, because otherwise a program which calls
`scanf' but not `read' might end up with an unexpected unresolved
reference to `read'.

   The way to address this problem was to first generate a set of
dependencies of one object file on another.  This was done by a shell
script called `lorder'.  The GNU tools don't provide a version of
lorder, as far as I know, but you can still find it in BSD
distributions.

   Then you ran `tsort' over the `lorder' output, and you used the
resulting sort to define the order in which you added objects to the
archive.

   This whole procedure has been obsolete since about 1980, because
Unix archives now contain a symbol table (traditionally built by
`ranlib', now generally built by `ar' itself), and the Unix linker uses
the symbol table to effectively make multiple passes over an archive
file.

   Anyhow, that's where tsort came from.  To solve an old problem with
the way the linker handled archive files, which has since been solved
in different ways.

File: coreutils.info,  Node: Operating on fields,  Next: Operating on characters,  Prev: Operating on sorted files,  Up: Top

8 Operating on fields
*********************

* Menu:

* cut invocation::              Print selected parts of lines.
* paste invocation::            Merge lines of files.
* join invocation::             Join lines on a common field.

File: coreutils.info,  Node: cut invocation,  Next: paste invocation,  Up: Operating on fields

8.1 `cut': Print selected parts of lines
========================================

`cut' writes to standard output selected parts of each line of each
input file, or standard input if no files are given or for a file name
of `-'.  Synopsis:

     cut OPTION... [FILE]...

   In the table which follows, the BYTE-LIST, CHARACTER-LIST, and
FIELD-LIST are one or more numbers or ranges (two numbers separated by
a dash) separated by commas.  Bytes, characters, and fields are
numbered starting at 1.  Incomplete ranges may be given: `-M' means
`1-M'; `N-' means `N' through end of line or last field.  The list
elements can be repeated, can overlap, and can be specified in any
order; but the selected input is written in the same order that it is
read, and is written exactly once.

   The program accepts the following options.  Also see *note Common
options::.

`-b BYTE-LIST'
`--bytes=BYTE-LIST'
     Select for printing only the bytes in positions listed in
     BYTE-LIST.  Tabs and backspaces are treated like any other
     character; they take up 1 byte.  If an output delimiter is
     specified, (see the description of `--output-delimiter'), then
     output that string between ranges of selected bytes.

`-c CHARACTER-LIST'
`--characters=CHARACTER-LIST'
     Select for printing only the characters in positions listed in
     CHARACTER-LIST.  The same as `-b' for now, but
     internationalization will change that.  Tabs and backspaces are
     treated like any other character; they take up 1 character.  If an
     output delimiter is specified, (see the description of
     `--output-delimiter'), then output that string between ranges of
     selected bytes.

`-f FIELD-LIST'
`--fields=FIELD-LIST'
     Select for printing only the fields listed in FIELD-LIST.  Fields
     are separated by a TAB character by default.  Also print any line
     that contains no delimiter character, unless the
     `--only-delimited' (`-s') option is specified

`-d INPUT_DELIM_BYTE'
`--delimiter=INPUT_DELIM_BYTE'
     With `-f', use the first byte of INPUT_DELIM_BYTE as the input
     fields separator (default is TAB).

`-n'
     Do not split multi-byte characters (no-op for now).

`-s'
`--only-delimited'
     For `-f', do not print lines that do not contain the field
     separator character.  Normally, any line without a field separator
     is printed verbatim.

`--output-delimiter=OUTPUT_DELIM_STRING'
     With `-f', output fields are separated by OUTPUT_DELIM_STRING.
     The default with `-f' is to use the input delimiter.  When using
     `-b' or `-c' to select ranges of byte or character offsets (as
     opposed to ranges of fields), output OUTPUT_DELIM_STRING between
     non-overlapping ranges of selected bytes.

`--complement'
     This option is a GNU extension.  Select for printing the
     complement of the bytes, characters or fields selected with the
     `-b', `-c' or `-f' options.  In other words, do _not_ print the
     bytes, characters or fields specified via those options.  This
     option is useful when you have many fields and want to print all
     but a few of them.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: paste invocation,  Next: join invocation,  Prev: cut invocation,  Up: Operating on fields

8.2 `paste': Merge lines of files
=================================

`paste' writes to standard output lines consisting of sequentially
corresponding lines of each given file, separated by a TAB character.
Standard input is used for a file name of `-' or if no input files are
given.

   For example:

     $ cat num2
     1
     2
     $ cat let3
     a
     b
     c
     $ paste num2 let3
     1       a
     2       b
             c

   Synopsis:

     paste [OPTION]... [FILE]...

   The program accepts the following options.  Also see *note Common
options::.

`-s'
`--serial'
     Paste the lines of one file at a time rather than one line from
     each file.  Using the above example data:

          $ paste -s num2 let3
          1       2
          a       b       c

`-d DELIM-LIST'
`--delimiters=DELIM-LIST'
     Consecutively use the characters in DELIM-LIST instead of TAB to
     separate merged lines.  When DELIM-LIST is exhausted, start again
     at its beginning.  Using the above example data:

          $ paste -d '%_' num2 let3 num2
          1%a_1
          2%b_2
          %c_


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: join invocation,  Prev: paste invocation,  Up: Operating on fields

8.3 `join': Join lines on a common field
========================================

`join' writes to standard output a line for each pair of input lines
that have identical join fields.  Synopsis:

     join [OPTION]... FILE1 FILE2

   Either FILE1 or FILE2 (but not both) can be `-', meaning standard
input.  FILE1 and FILE2 should be sorted on the join fields.

   Normally, the sort order is that of the collating sequence specified
by the `LC_COLLATE' locale.  Unless the `-t' option is given, the sort
comparison ignores blanks at the start of the join field, as in `sort
-b'.  If the `--ignore-case' option is given, the sort comparison
ignores the case of characters in the join field, as in `sort -f'.

   The `sort' and `join' commands should use consistent locales and
options if the output of `sort' is fed to `join'.  You can use a
command like `sort -k 1b,1' to sort a file on its default join field,
but if you select a non-default locale, join field, separator, or
comparison options, then you should do so consistently between `join'
and `sort'.

   If the input has no unpairable lines, a GNU extension is available;
the sort order can be any order that considers two fields to be equal
if and only if the sort comparison described above considers them to be
equal.  For example:

     $ cat file1
     a a1
     c c1
     b b1
     $ cat file2
     a a2
     c c2
     b b2
     $ join file1 file2
     a a1 a2
     c c1 c2
     b b1 b2

   If the `--check-order' option is given, unsorted inputs will cause a
fatal error message.  If the option `--nocheck-order' is given,
unsorted inputs will never cause an error message.  If neither of these
options is given, wrongly sorted inputs are diagnosed only if an input
file is found to contain unpairable lines.  If an input file is
diagnosed as being unsorted, the `join' command will exit with a
nonzero status (and the output should not be used).

   Forcing `join' to process wrongly sorted input files containing
unpairable lines by specifying `--nocheck-order' is not guaranteed to
produce any particular output.  The output will probably not correspond
with whatever you hoped it would be.

   The defaults are:
   * the join field is the first field in each line;

   * fields in the input are separated by one or more blanks, with
     leading blanks on the line ignored;

   * fields in the output are separated by a space;

   * each output line consists of the join field, the remaining fields
     from FILE1, then the remaining fields from FILE2.

   The program accepts the following options.  Also see *note Common
options::.

`-a FILE-NUMBER'
     Print a line for each unpairable line in file FILE-NUMBER (either
     `1' or `2'), in addition to the normal output.

`--check-order'
     Fail with an error message if either input file is wrongly ordered.

`--nocheck-order'
     Do not check that both input files are in sorted order.  This is
     the default.

`-e STRING'
     Replace those output fields that are missing in the input with
     STRING.

`-i'
`--ignore-case'
     Ignore differences in case when comparing keys.  With this option,
     the lines of the input files must be ordered in the same way.  Use
     `sort -f' to produce this ordering.

`-1 FIELD'
     Join on field FIELD (a positive integer) of file 1.

`-2 FIELD'
     Join on field FIELD (a positive integer) of file 2.

`-j FIELD'
     Equivalent to `-1 FIELD -2 FIELD'.

`-o FIELD-LIST'
     Construct each output line according to the format in FIELD-LIST.
     Each element in FIELD-LIST is either the single character `0' or
     has the form M.N where the file number, M, is `1' or `2' and N is
     a positive field number.

     A field specification of `0' denotes the join field.  In most
     cases, the functionality of the `0' field spec may be reproduced
     using the explicit M.N that corresponds to the join field.
     However, when printing unpairable lines (using either of the `-a'
     or `-v' options), there is no way to specify the join field using
     M.N in FIELD-LIST if there are unpairable lines in both files.  To
     give `join' that functionality, POSIX invented the `0' field
     specification notation.

     The elements in FIELD-LIST are separated by commas or blanks.
     Blank separators typically need to be quoted for the shell.  For
     example, the commands `join -o 1.2,2.2' and `join -o '1.2 2.2''
     are equivalent.

     All output lines--including those printed because of any -a or -v
     option--are subject to the specified FIELD-LIST.

`-t CHAR'
     Use character CHAR as the input and output field separator.  Treat
     as significant each occurrence of CHAR in the input file.  Use
     `sort -t CHAR', without the `-b' option of `sort', to produce this
     ordering.

`-v FILE-NUMBER'
     Print a line for each unpairable line in file FILE-NUMBER (either
     `1' or `2'), instead of the normal output.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: Operating on characters,  Next: Directory listing,  Prev: Operating on fields,  Up: Top

9 Operating on characters
*************************

This commands operate on individual characters.

* Menu:

* tr invocation::               Translate, squeeze, and/or delete characters.
* expand invocation::           Convert tabs to spaces.
* unexpand invocation::         Convert spaces to tabs.

File: coreutils.info,  Node: tr invocation,  Next: expand invocation,  Up: Operating on characters

9.1 `tr': Translate, squeeze, and/or delete characters
======================================================

Synopsis:

     tr [OPTION]... SET1 [SET2]

   `tr' copies standard input to standard output, performing one of the
following operations:

   * translate, and optionally squeeze repeated characters in the
     result,

   * squeeze repeated characters,

   * delete characters,

   * delete characters, then squeeze repeated characters from the
     result.

   The SET1 and (if given) SET2 arguments define ordered sets of
characters, referred to below as SET1 and SET2.  These sets are the
characters of the input that `tr' operates on.  The `--complement'
(`-c', `-C') option replaces SET1 with its complement (all of the
characters that are not in SET1).

   Currently `tr' fully supports only single-byte characters.
Eventually it will support multibyte characters; when it does, the `-C'
option will cause it to complement the set of characters, whereas `-c'
will cause it to complement the set of values.  This distinction will
matter only when some values are not characters, and this is possible
only in locales using multibyte encodings when the input contains
encoding errors.

   The program accepts the `--help' and `--version' options.  *Note
Common options::.  Options must precede operands.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

* Menu:

* Character sets::              Specifying sets of characters.
* Translating::                 Changing one set of characters to another.
* Squeezing::                   Squeezing repeats and deleting.

File: coreutils.info,  Node: Character sets,  Next: Translating,  Up: tr invocation

9.1.1 Specifying sets of characters
-----------------------------------

The format of the SET1 and SET2 arguments resembles the format of
regular expressions; however, they are not regular expressions, only
lists of characters.  Most characters simply represent themselves in
these strings, but the strings can contain the shorthands listed below,
for convenience.  Some of them can be used only in SET1 or SET2, as
noted below.

Backslash escapes
     The following backslash escape sequences are recognized:

    `\a'
          Control-G.

    `\b'
          Control-H.

    `\f'
          Control-L.

    `\n'
          Control-J.

    `\r'
          Control-M.

    `\t'
          Control-I.

    `\v'
          Control-K.

    `\OOO'
          The 8-bit character with the value given by OOO, which is 1
          to 3 octal digits.  Note that `\400' is interpreted as the
          two-byte sequence, `\040' `0'.

    `\\'
          A backslash.

     While a backslash followed by a character not listed above is
     interpreted as that character, the backslash also effectively
     removes any special significance, so it is useful to escape `[',
     `]', `*', and `-'.

Ranges
     The notation `M-N' expands to all of the characters from M through
     N, in ascending order.  M should collate before N; if it doesn't,
     an error results.  As an example, `0-9' is the same as
     `0123456789'.

     GNU `tr' does not support the System V syntax that uses square
     brackets to enclose ranges.  Translations specified in that format
     sometimes work as expected, since the brackets are often
     transliterated to themselves.  However, they should be avoided
     because they sometimes behave unexpectedly.  For example, `tr -d
     '[0-9]'' deletes brackets as well as digits.

     Many historically common and even accepted uses of ranges are not
     portable.  For example, on EBCDIC hosts using the `A-Z' range will
     not do what most would expect because `A' through `Z' are not
     contiguous as they are in ASCII.  If you can rely on a POSIX
     compliant version of `tr', then the best way to work around this
     is to use character classes (see below).  Otherwise, it is most
     portable (and most ugly) to enumerate the members of the ranges.

Repeated characters
     The notation `[C*N]' in SET2 expands to N copies of character C.
     Thus, `[y*6]' is the same as `yyyyyy'.  The notation `[C*]' in
     STRING2 expands to as many copies of C as are needed to make SET2
     as long as SET1.  If N begins with `0', it is interpreted in
     octal, otherwise in decimal.

Character classes
     The notation `[:CLASS:]' expands to all of the characters in the
     (predefined) class CLASS.  The characters expand in no particular
     order, except for the `upper' and `lower' classes, which expand in
     ascending order.  When the `--delete' (`-d') and
     `--squeeze-repeats' (`-s') options are both given, any character
     class can be used in SET2.  Otherwise, only the character classes
     `lower' and `upper' are accepted in SET2, and then only if the
     corresponding character class (`upper' and `lower', respectively)
     is specified in the same relative position in SET1.  Doing this
     specifies case conversion.  The class names are given below; an
     error results when an invalid class name is given.

    `alnum'
          Letters and digits.

    `alpha'
          Letters.

    `blank'
          Horizontal whitespace.

    `cntrl'
          Control characters.

    `digit'
          Digits.

    `graph'
          Printable characters, not including space.

    `lower'
          Lowercase letters.

    `print'
          Printable characters, including space.

    `punct'
          Punctuation characters.

    `space'
          Horizontal or vertical whitespace.

    `upper'
          Uppercase letters.

    `xdigit'
          Hexadecimal digits.

Equivalence classes
     The syntax `[=C=]' expands to all of the characters that are
     equivalent to C, in no particular order.  Equivalence classes are
     a relatively recent invention intended to support non-English
     alphabets.  But there seems to be no standard way to define them
     or determine their contents.  Therefore, they are not fully
     implemented in GNU `tr'; each character's equivalence class
     consists only of that character, which is of no particular use.


File: coreutils.info,  Node: Translating,  Next: Squeezing,  Prev: Character sets,  Up: tr invocation

9.1.2 Translating
-----------------

`tr' performs translation when SET1 and SET2 are both given and the
`--delete' (`-d') option is not given.  `tr' translates each character
of its input that is in SET1 to the corresponding character in SET2.
Characters not in SET1 are passed through unchanged.  When a character
appears more than once in SET1 and the corresponding characters in SET2
are not all the same, only the final one is used.  For example, these
two commands are equivalent:

     tr aaa xyz
     tr a z

   A common use of `tr' is to convert lowercase characters to
uppercase.  This can be done in many ways.  Here are three of them:

     tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
     tr a-z A-Z
     tr '[:lower:]' '[:upper:]'

But note that using ranges like `a-z' above is not portable.

   When `tr' is performing translation, SET1 and SET2 typically have
the same length.  If SET1 is shorter than SET2, the extra characters at
the end of SET2 are ignored.

   On the other hand, making SET1 longer than SET2 is not portable;
POSIX says that the result is undefined.  In this situation, BSD `tr'
pads SET2 to the length of SET1 by repeating the last character of SET2
as many times as necessary.  System V `tr' truncates SET1 to the length
of SET2.

   By default, GNU `tr' handles this case like BSD `tr'.  When the
`--truncate-set1' (`-t') option is given, GNU `tr' handles this case
like the System V `tr' instead.  This option is ignored for operations
other than translation.

   Acting like System V `tr' in this case breaks the relatively common
BSD idiom:

     tr -cs A-Za-z0-9 '\012'

because it converts only zero bytes (the first element in the
complement of SET1), rather than all non-alphanumerics, to newlines.

By the way, the above idiom is not portable because it uses ranges, and
it assumes that the octal code for newline is 012.  Assuming a POSIX
compliant `tr', here is a better way to write it:

     tr -cs '[:alnum:]' '[\n*]'

File: coreutils.info,  Node: Squeezing,  Prev: Translating,  Up: tr invocation

9.1.3 Squeezing repeats and deleting
------------------------------------

When given just the `--delete' (`-d') option, `tr' removes any input
characters that are in SET1.

   When given just the `--squeeze-repeats' (`-s') option, `tr' replaces
each input sequence of a repeated character that is in SET1 with a
single occurrence of that character.

   When given both `--delete' and `--squeeze-repeats', `tr' first
performs any deletions using SET1, then squeezes repeats from any
remaining characters using SET2.

   The `--squeeze-repeats' option may also be used when translating, in
which case `tr' first performs translation, then squeezes repeats from
any remaining characters using SET2.

   Here are some examples to illustrate various combinations of options:

   * Remove all zero bytes:

          tr -d '\0'

   * Put all words on lines by themselves.  This converts all
     non-alphanumeric characters to newlines, then squeezes each string
     of repeated newlines into a single newline:

          tr -cs '[:alnum:]' '[\n*]'

   * Convert each sequence of repeated newlines to a single newline:

          tr -s '\n'

   * Find doubled occurrences of words in a document.  For example,
     people often write "the the" with the repeated words separated by
     a newline.  The Bourne shell script below works first by
     converting each sequence of punctuation and blank characters to a
     single newline.  That puts each "word" on a line by itself.  Next
     it maps all uppercase characters to lower case, and finally it
     runs `uniq' with the `-d' option to print out only the words that
     were repeated.

          #!/bin/sh
          cat -- "$@" \
            | tr -s '[:punct:][:blank:]' '[\n*]' \
            | tr '[:upper:]' '[:lower:]' \
            | uniq -d

   * Deleting a small set of characters is usually straightforward.
     For example, to remove all `a's, `x's, and `M's you would do this:

          tr -d axM

     However, when `-' is one of those characters, it can be tricky
     because `-' has special meanings.  Performing the same task as
     above but also removing all `-' characters, we might try `tr -d
     -axM', but that would fail because `tr' would try to interpret
     `-a' as a command-line option.  Alternatively, we could try
     putting the hyphen inside the string, `tr -d a-xM', but that
     wouldn't work either because it would make `tr' interpret `a-x' as
     the range of characters `a'...`x' rather than the three.  One way
     to solve the problem is to put the hyphen at the end of the list
     of characters:

          tr -d axM-

     Or you can use `--' to terminate option processing:

          tr -d -- -axM

     More generally, use the character class notation `[=c=]' with `-'
     (or any other character) in place of the `c':

          tr -d '[=-=]axM'

     Note how single quotes are used in the above example to protect the
     square brackets from interpretation by a shell.


File: coreutils.info,  Node: expand invocation,  Next: unexpand invocation,  Prev: tr invocation,  Up: Operating on characters

9.2 `expand': Convert tabs to spaces
====================================

`expand' writes the contents of each given FILE, or standard input if
none are given or for a FILE of `-', to standard output, with tab
characters converted to the appropriate number of spaces.  Synopsis:

     expand [OPTION]... [FILE]...

   By default, `expand' converts all tabs to spaces.  It preserves
backspace characters in the output; they decrement the column count for
tab calculations.  The default action is equivalent to `-t 8' (set tabs
every 8 columns).

   The program accepts the following options.  Also see *note Common
options::.

`-t TAB1[,TAB2]...'
`--tabs=TAB1[,TAB2]...'
     If only one tab stop is given, set the tabs TAB1 spaces apart
     (default is 8).  Otherwise, set the tabs at columns TAB1, TAB2,
     ... (numbered from 0), and replace any tabs beyond the last tab
     stop given with single spaces.  Tab stops can be separated by
     blanks as well as by commas.

     For compatibility, GNU `expand' also accepts the obsolete option
     syntax, `-T1[,T2]...'.  New scripts should use `-t T1[,T2]...'
     instead.

`-i'
`--initial'
     Only convert initial tabs (those that precede all non-space or
     non-tab characters) on each line to spaces.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: unexpand invocation,  Prev: expand invocation,  Up: Operating on characters

9.3 `unexpand': Convert spaces to tabs
======================================

`unexpand' writes the contents of each given FILE, or standard input if
none are given or for a FILE of `-', to standard output, converting
blanks at the beginning of each line into as many tab characters as
needed.  In the default POSIX locale, a "blank" is a space or a tab;
other locales may specify additional blank characters.  Synopsis:

     unexpand [OPTION]... [FILE]...

   By default, `unexpand' converts only initial blanks (those that
precede all non-blank characters) on each line.  It preserves backspace
characters in the output; they decrement the column count for tab
calculations.  By default, tabs are set at every 8th column.

   The program accepts the following options.  Also see *note Common
options::.

`-t TAB1[,TAB2]...'
`--tabs=TAB1[,TAB2]...'
     If only one tab stop is given, set the tabs TAB1 columns apart
     instead of the default 8.  Otherwise, set the tabs at columns
     TAB1, TAB2, ... (numbered from 0), and leave blanks beyond the tab
     stops given unchanged.  Tab stops can be separated by blanks as
     well as by commas.  This option implies the `-a' option.

     For compatibility, GNU `unexpand' supports the obsolete option
     syntax, `-TAB1[,TAB2]...', where tab stops must be separated by
     commas.  (Unlike `-t', this obsolete option does not imply `-a'.)
     New scripts should use `--first-only -t TAB1[,TAB2]...' instead.

`-a'
`--all'
     Also convert all sequences of two or more blanks just before a tab
     stop, even if they occur after non-blank characters in a line.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: Directory listing,  Next: Basic operations,  Prev: Operating on characters,  Up: Top

10 Directory listing
********************

This chapter describes the `ls' command and its variants `dir' and
`vdir', which list information about files.

* Menu:

* ls invocation::               List directory contents.
* dir invocation::              Briefly ls.
* vdir invocation::             Verbosely ls.
* dircolors invocation::        Color setup for ls, etc.

File: coreutils.info,  Node: ls invocation,  Next: dir invocation,  Up: Directory listing

10.1 `ls': List directory contents
==================================

The `ls' program lists information about files (of any type, including
directories).  Options and file arguments can be intermixed
arbitrarily, as usual.

   For non-option command-line arguments that are directories, by
default `ls' lists the contents of directories, not recursively, and
omitting files with names beginning with `.'.  For other non-option
arguments, by default `ls' lists just the file name.  If no non-option
argument is specified, `ls' operates on the current directory, acting
as if it had been invoked with a single argument of `.'.

   By default, the output is sorted alphabetically, according to the
locale settings in effect.(1) If standard output is a terminal, the
output is in columns (sorted vertically) and control characters are
output as question marks; otherwise, the output is listed one per line
and control characters are output as-is.

   Because `ls' is such a fundamental program, it has accumulated many
options over the years.  They are described in the subsections below;
within each section, options are listed alphabetically (ignoring case).
The division of options into the subsections is not absolute, since some
options affect more than one aspect of `ls''s operation.

   Exit status:

     0 success
     1 minor problems  (e.g., failure to access a file or directory not
       specified as a command line argument.  This happens when listing a
       directory in which entries are actively being removed or renamed.)
     2 serious trouble (e.g., memory exhausted, invalid option, failure
       to access a file or directory specified as a command line argument
       or a directory loop)

   Also see *note Common options::.

* Menu:

* Which files are listed::
* What information is listed::
* Sorting the output::
* Details about version sort::
* General output formatting::
* Formatting file timestamps::
* Formatting the file names::

   ---------- Footnotes ----------

   (1) If you use a non-POSIX locale (e.g., by setting `LC_ALL' to
`en_US'), then `ls' may produce output that is sorted differently than
you're accustomed to.  In that case, set the `LC_ALL' environment
variable to `C'.

File: coreutils.info,  Node: Which files are listed,  Next: What information is listed,  Up: ls invocation

10.1.1 Which files are listed
-----------------------------

These options determine which files `ls' lists information for.  By
default, `ls' lists files and the contents of any directories on the
command line, except that in directories it ignores files whose names
start with `.'.

`-a'
`--all'
     In directories, do not ignore file names that start with `.'.

`-A'
`--almost-all'
     In directories, do not ignore all file names that start with `.';
     ignore only `.' and `..'.  The `--all' (`-a') option overrides
     this option.

`-B'
`--ignore-backups'
     In directories, ignore files that end with `~'.  This option is
     equivalent to `--ignore='*~' --ignore='.*~''.

`-d'
`--directory'
     List just the names of directories, as with other types of files,
     rather than listing their contents.  Do not follow symbolic links
     listed on the command line unless the `--dereference-command-line'
     (`-H'), `--dereference' (`-L'), or
     `--dereference-command-line-symlink-to-dir' options are specified.

`-H'
`--dereference-command-line'
     If a command line argument specifies a symbolic link, show
     information for the file the link references rather than for the
     link itself.

`--dereference-command-line-symlink-to-dir'
     Do not dereference symbolic links, with one exception: if a
     command line argument specifies a symbolic link that refers to a
     directory, show information for that directory rather than for the
     link itself.  This is the default behavior when no other
     dereferencing-related option has been specified (`--classify'
     (`-F'), `--directory' (`-d'), (`-l'), `--dereference' (`-L'), or
     `--dereference-command-line' (`-H')).

`--group-directories-first'
     Group all the directories before the files and then sort the
     directories and the files separately using the selected sort key
     (see -sort option).  That is, this option specifies a primary sort
     key, and the -sort option specifies a secondary key.  However, any
     use of `--sort=none' (`-U') disables this option altogether.

`--hide=PATTERN'
     In directories, ignore files whose names match the shell pattern
     PATTERN, unless the `--all' (`-a') or `--almost-all' (`-A') is
     also given.  This option acts like `--ignore=PATTERN' except that
     it has no effect if `--all' (`-a') or `--almost-all' (`-A') is
     also given.

     This option can be useful in shell aliases.  For example, if `lx'
     is an alias for `ls --hide='*~'' and `ly' is an alias for `ls
     --ignore='*~'', then the command `lx -A' lists the file `README~'
     even though `ly -A' would not.

`-I PATTERN'
`--ignore=PATTERN'
     In directories, ignore files whose names match the shell pattern
     (not regular expression) PATTERN.  As in the shell, an initial `.'
     in a file name does not match a wildcard at the start of PATTERN.
     Sometimes it is useful to give this option several times.  For
     example,

          $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'

     The first option ignores names of length 3 or more that start with
     `.', the second ignores all two-character names that start with `.'
     except `..', and the third ignores names that start with `#'.

`-L'
`--dereference'
     When showing file information for a symbolic link, show information
     for the file the link references rather than the link itself.
     However, even with this option, `ls' still prints the name of the
     link itself, not the name of the file that the link points to.

`-R'
`--recursive'
     List the contents of all directories recursively.


File: coreutils.info,  Node: What information is listed,  Next: Sorting the output,  Prev: Which files are listed,  Up: ls invocation

10.1.2 What information is listed
---------------------------------

These options affect the information that `ls' displays.  By default,
only file names are shown.

`--author'
     List each file's author when producing long format directory
     listings.  In GNU/Hurd, file authors can differ from their owners,
     but in other operating systems the two are the same.

`-D'
`--dired'
     With the long listing (`-l') format, print an additional line after
     the main output:

          //DIRED// BEG1 END1 BEG2 END2 ...

     The BEGN and ENDN are unsigned integers that record the byte
     position of the beginning and end of each file name in the output.
     This makes it easy for Emacs to find the names, even when they
     contain unusual characters such as space or newline, without fancy
     searching.

     If directories are being listed recursively (`-R'), output a
     similar line with offsets for each subdirectory name:

          //SUBDIRED// BEG1 END1 ...

     Finally, output a line of the form:

          //DIRED-OPTIONS// --quoting-style=WORD

     where WORD is the quoting style (*note Formatting the file
     names::).

     Here is an actual example:

          $ mkdir -p a/sub/deeper a/sub2
          $ touch a/f1 a/f2
          $ touch a/sub/deeper/file
          $ ls -gloRF --dired a
            a:
            total 8
            -rw-r--r-- 1    0 Jun 10 12:27 f1
            -rw-r--r-- 1    0 Jun 10 12:27 f2
            drwxr-xr-x 3 4096 Jun 10 12:27 sub/
            drwxr-xr-x 2 4096 Jun 10 12:27 sub2/

            a/sub:
            total 4
            drwxr-xr-x 2 4096 Jun 10 12:27 deeper/

            a/sub/deeper:
            total 0
            -rw-r--r-- 1 0 Jun 10 12:27 file

            a/sub2:
            total 0
          //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
          //SUBDIRED// 2 3 167 172 228 240 290 296
          //DIRED-OPTIONS// --quoting-style=literal

     Note that the pairs of offsets on the `//DIRED//' line above
     delimit these names: `f1', `f2', `sub', `sub2', `deeper', `file'.
     The offsets on the `//SUBDIRED//' line delimit the following
     directory names: `a', `a/sub', `a/sub/deeper', `a/sub2'.

     Here is an example of how to extract the fifth entry name,
     `deeper', corresponding to the pair of offsets, 222 and 228:

          $ ls -gloRF --dired a > out
          $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
          deeper

     Note that although the listing above includes a trailing slash for
     the `deeper' entry, the offsets select the name without the
     trailing slash.  However, if you invoke `ls' with `--dired' along
     with an option like `--escape' (aka `-b') and operate on a file
     whose name contains special characters, notice that the backslash
     _is_ included:

          $ touch 'a b'
          $ ls -blog --dired 'a b'
            -rw-r--r-- 1 0 Jun 10 12:28 a\ b
          //DIRED// 30 34
          //DIRED-OPTIONS// --quoting-style=escape

     If you use a quoting style that adds quote marks (e.g.,
     `--quoting-style=c'), then the offsets include the quote marks.
     So beware that the user may select the quoting style via the
     environment variable `QUOTING_STYLE'.  Hence, applications using
     `--dired' should either specify an explicit
     `--quoting-style=literal' option (aka `-N' or `--literal') on the
     command line, or else be prepared to parse the escaped names.

`--full-time'
     Produce long format directory listings, and list times in full.
     It is equivalent to using `--format=long' with
     `--time-style=full-iso' (*note Formatting file timestamps::).

`-g'
     Produce long format directory listings, but don't display owner
     information.

`-G'
`--no-group'
     Inhibit display of group information in a long format directory
     listing.  (This is the default in some non-GNU versions of `ls',
     so we provide this option for compatibility.)

`-h'
`--human-readable'
     Append a size letter to each size, such as `M' for mebibytes.
     Powers of 1024 are used, not 1000; `M' stands for 1,048,576 bytes.
     This option is equivalent to `--block-size=human-readable'.  Use
     the `--si' option if you prefer powers of 1000.

`-i'
`--inode'
     Print the inode number (also called the file serial number and
     index number) of each file to the left of the file name.  (This
     number uniquely identifies each file within a particular file
     system.)

`-l'
`--format=long'
`--format=verbose'
     In addition to the name of each file, print the file type, file
     mode bits, number of hard links, owner name, group name, size, and
     timestamp (*note Formatting file timestamps::), normally the
     modification time.  Print question marks for information that
     cannot be determined.

     Normally the size is printed as a byte count without punctuation,
     but this can be overridden (*note Block size::).  For example, `-h'
     prints an abbreviated, human-readable count, and
     `--block-size="'1"' prints a byte count with the thousands
     separator of the current locale.

     For each directory that is listed, preface the files with a line
     `total BLOCKS', where BLOCKS is the total disk allocation for all
     files in that directory.  The block size currently defaults to 1024
     bytes, but this can be overridden (*note Block size::).  The
     BLOCKS computed counts each hard link separately; this is arguably
     a deficiency.

     The file type is one of the following characters:

    `-'
          regular file

    `b'
          block special file

    `c'
          character special file

    `C'
          high performance ("contiguous data") file

    `d'
          directory

    `D'
          door (Solaris 2.5 and up)

    `l'
          symbolic link

    `M'
          off-line ("migrated") file (Cray DMF)

    `n'
          network special file (HP-UX)

    `p'
          FIFO (named pipe)

    `P'
          port (Solaris 10 and up)

    `s'
          socket

    `?'
          some other file type

     The file mode bits listed are similar to symbolic mode
     specifications (*note Symbolic Modes::).  But `ls' combines
     multiple bits into the third character of each set of permissions
     as follows:

    `s'
          If the set-user-ID or set-group-ID bit and the corresponding
          executable bit are both set.

    `S'
          If the set-user-ID or set-group-ID bit is set but the
          corresponding executable bit is not set.

    `t'
          If the restricted deletion flag or sticky bit, and the
          other-executable bit, are both set.  The restricted deletion
          flag is another name for the sticky bit.  *Note Mode
          Structure::.

    `T'
          If the restricted deletion flag or sticky bit is set but the
          other-executable bit is not set.

    `x'
          If the executable bit is set and none of the above apply.

    `-'
          Otherwise.

     Following the file mode bits is a single character that specifies
     whether an alternate access method such as an access control list
     applies to the file.  When the character following the file mode
     bits is a space, there is no alternate access method.  When it is
     a printing character, then there is such a method.

     GNU `ls' uses a `.' character to indicate a file with an SELinux
     security context, but no other alternate access method.

     A file with any other combination of alternate access methods is
     marked with a `+' character.

`-n'
`--numeric-uid-gid'
     Produce long format directory listings, but display numeric user
     and group IDs instead of the owner and group names.

`-o'
     Produce long format directory listings, but don't display group
     information.  It is equivalent to using `--format=long' with
     `--no-group' .

`-s'
`--size'
     Print the disk allocation of each file to the left of the file
     name.  This is the amount of disk space used by the file, which is
     usually a bit more than the file's size, but it can be less if the
     file has holes.

     Normally the disk allocation is printed in units of 1024 bytes,
     but this can be overridden (*note Block size::).

     For files that are NFS-mounted from an HP-UX system to a BSD
     system, this option reports sizes that are half the correct
     values.  On HP-UX systems, it reports sizes that are twice the
     correct values for files that are NFS-mounted from BSD systems.
     This is due to a flaw in HP-UX; it also affects the HP-UX `ls'
     program.

`--si'
     Append an SI-style abbreviation to each size, such as `M' for
     megabytes.  Powers of 1000 are used, not 1024; `M' stands for
     1,000,000 bytes.  This option is equivalent to `--block-size=si'.
     Use the `-h' or `--human-readable' option if you prefer powers of
     1024.

`-Z'
`--context'
     Display the SELinux security context or `?' if none is found.
     When used with the `-l' option, print the security context to the
     left of the size column.

     Note: When multiple format options are used in `ls', the last one
     is used. Therefore `ls -lZ' (security format is last - same as `ls
     --context') differs from `ls -Zl' (long format with selinux
     context is shown, same as `ls --lcontext')


File: coreutils.info,  Node: Sorting the output,  Next: Details about version sort,  Prev: What information is listed,  Up: ls invocation

10.1.3 Sorting the output
-------------------------

These options change the order in which `ls' sorts the information it
outputs.  By default, sorting is done by character code (e.g., ASCII
order).

`-c'
`--time=ctime'
`--time=status'
     If the long listing format (e.g., `-l', `-o') is being used, print
     the status change time (the `ctime' in the inode) instead of the
     modification time.  When explicitly sorting by time (`--sort=time'
     or `-t') or when not using a long listing format, sort according
     to the status change time.

`-f'
     Primarily, like `-U'--do not sort; list the files in whatever
     order they are stored in the directory.  But also enable `-a' (list
     all files) and disable `-l', `--color', and `-s' (if they were
     specified before the `-f').

`-r'
`--reverse'
     Reverse whatever the sorting method is--e.g., list files in reverse
     alphabetical order, youngest first, smallest first, or whatever.

`-S'
`--sort=size'
     Sort by file size, largest first.

`-t'
`--sort=time'
     Sort by modification time (the `mtime' in the inode), newest first.

`-u'
`--time=atime'
`--time=access'
`--time=use'
     If the long listing format (e.g., `--format=long') is being used,
     print the last access time (the `atime' in the inode).  When
     explicitly sorting by time (`--sort=time' or `-t') or when not
     using a long listing format, sort according to the access time.

`-U'
`--sort=none'
     Do not sort; list the files in whatever order they are stored in
     the directory.  (Do not do any of the other unrelated things that
     `-f' does.)  This is especially useful when listing very large
     directories, since not doing any sorting can be noticeably faster.

`-v'
`--sort=version'
     Sort by version name and number, lowest first.  It behaves like a
     default sort, except that each sequence of decimal digits is
     treated numerically as an index/version number.  (*Note Details
     about version sort::.)

`-X'
`--sort=extension'
     Sort directory contents alphabetically by file extension
     (characters after the last `.'); files with no extension are
     sorted first.


File: coreutils.info,  Node: Details about version sort,  Next: General output formatting,  Prev: Sorting the output,  Up: ls invocation

10.1.4 Details about version sort
---------------------------------

Version sorting handles the fact that file names frequently include
indices or version numbers.  Standard sorting usually does not produce
the order that one expects because comparisons are made on a
character-by-character basis.  Version sorting is especially useful
when browsing directories that contain many files with indices/version
numbers in their names:

     $ ls -1            $ ls -1v
     abc.zml-1.gz       abc.zml-1.gz
     abc.zml-12.gz      abc.zml-2.gz
     abc.zml-2.gz       abc.zml-12.gz

   Version-sorted strings are compared such that if VER1 and VER2 are
version numbers and PREFIX and SUFFIX (SUFFIX matching the regular
expression `(\.[A-Za-z~][A-Za-z0-9~]*)*') are strings then VER1 < VER2
implies that the name composed of "PREFIX VER1 SUFFIX" sorts before
"PREFIX VER2 SUFFIX".

   Note also that leading zeros of numeric parts are ignored:

     $ ls -1            $ ls -1v
     abc-1.007.tgz      abc-1.01a.tgz
     abc-1.012b.tgz     abc-1.007.tgz
     abc-1.01a.tgz      abc-1.012b.tgz

   This functionality is implemented using gnulib's `filevercmp'
function, which has some caveats worth noting.

   * `LC_COLLATE' is ignored, which means `ls -v' and `sort -V' will
     sort non-numeric prefixes as if the `LC_COLLATE' locale category
     was set to `C'.

   * Some suffixes will not be matched by the regular expression
     mentioned above.  Consequently these examples may not sort as you
     expect:

          abc-1.2.3.4.7z
          abc-1.2.3.7z

          abc-1.2.3.4.x86_64.rpm
          abc-1.2.3.x86_64.rpm

File: coreutils.info,  Node: General output formatting,  Next: Formatting file timestamps,  Prev: Details about version sort,  Up: ls invocation

10.1.5 General output formatting
--------------------------------

These options affect the appearance of the overall output.

`-1'
`--format=single-column'
     List one file per line.  This is the default for `ls' when standard
     output is not a terminal.

`-C'
`--format=vertical'
     List files in columns, sorted vertically.  This is the default for
     `ls' if standard output is a terminal.  It is always the default
     for the `dir' program.  GNU `ls' uses variable width columns to
     display as many files as possible in the fewest lines.

`--color [=WHEN]'
     Specify whether to use color for distinguishing file types.  WHEN
     may be omitted, or one of:
        * none - Do not use color at all.  This is the default.

        * auto - Only use color if standard output is a terminal.

        * always - Always use color.
     Specifying `--color' and no WHEN is equivalent to `--color=always'.
     Piping a colorized listing through a pager like `more' or `less'
     usually produces unreadable results.  However, using `more -f'
     does seem to work.

`-F'
`--classify'
`--indicator-style=classify'
     Append a character to each file name indicating the file type.
     Also, for regular files that are executable, append `*'.  The file
     type indicators are `/' for directories, `@' for symbolic links,
     `|' for FIFOs, `=' for sockets, `>' for doors, and nothing for
     regular files.  Do not follow symbolic links listed on the command
     line unless the `--dereference-command-line' (`-H'),
     `--dereference' (`-L'), or
     `--dereference-command-line-symlink-to-dir' options are specified.

`--file-type'
`--indicator-style=file-type'
     Append a character to each file name indicating the file type.
     This is like `-F', except that executables are not marked.

`--indicator-style=WORD'
     Append a character indicator with style WORD to entry names, as
     follows:

    `none'
          Do not append any character indicator; this is the default.

    `slash'
          Append `/' for directories.  This is the same as the `-p'
          option.

    `file-type'
          Append `/' for directories, `@' for symbolic links, `|' for
          FIFOs, `=' for sockets, and nothing for regular files.  This
          is the same as the `--file-type' option.

    `classify'
          Append `*' for executable regular files, otherwise behave as
          for `file-type'.  This is the same as the `-F' or
          `--classify' option.

`-k'
     Print file sizes in 1024-byte blocks, overriding the default block
     size (*note Block size::).  This option is equivalent to
     `--block-size=1K'.

`-m'
`--format=commas'
     List files horizontally, with as many as will fit on each line,
     separated by `, ' (a comma and a space).

`-p'
`--indicator-style=slash'
     Append a `/' to directory names.

`-x'
`--format=across'
`--format=horizontal'
     List the files in columns, sorted horizontally.

`-T COLS'
`--tabsize=COLS'
     Assume that each tab stop is COLS columns wide.  The default is 8.
     `ls' uses tabs where possible in the output, for efficiency.  If
     COLS is zero, do not use tabs at all.

     Some terminal emulators (at least Apple Terminal 1.5 (133) from
     Mac OS X 10.4.8) do not properly align columns to the right of a
     TAB following a non-ASCII byte.  If you use such a terminal
     emulator, use the `-T0' option or put `TABSIZE=0' in your
     environment to tell `ls' to align using spaces, not tabs.

`-w'
`--width=COLS'
     Assume the screen is COLS columns wide.  The default is taken from
     the terminal settings if possible; otherwise the environment
     variable `COLUMNS' is used if it is set; otherwise the default is
     80.


File: coreutils.info,  Node: Formatting file timestamps,  Next: Formatting the file names,  Prev: General output formatting,  Up: ls invocation

10.1.6 Formatting file timestamps
---------------------------------

By default, file timestamps are listed in abbreviated form.  Most
locales use a timestamp like `2002-03-30 23:45'.  However, the default
POSIX locale uses a date like `Mar 30  2002' for non-recent timestamps,
and a date-without-year and time like `Mar 30 23:45' for recent
timestamps.

   A timestamp is considered to be "recent" if it is less than six
months old, and is not dated in the future.  If a timestamp dated today
is not listed in recent form, the timestamp is in the future, which
means you probably have clock skew problems which may break programs
like `make' that rely on file timestamps.

   Time stamps are listed according to the time zone rules specified by
the `TZ' environment variable, or by the system default rules if `TZ'
is not set.  *Note Specifying the Time Zone with `TZ': (libc)TZ
Variable.

   The following option changes how file timestamps are printed.

`--time-style=STYLE'
     List timestamps in style STYLE.  The STYLE should be one of the
     following:

    `+FORMAT'
          List timestamps using FORMAT, where FORMAT is interpreted
          like the format argument of `date' (*note date invocation::).
          For example, `--time-style="+%Y-%m-%d %H:%M:%S"' causes `ls'
          to list timestamps like `2002-03-30 23:45:56'.  As with
          `date', FORMAT's interpretation is affected by the `LC_TIME'
          locale category.

          If FORMAT contains two format strings separated by a newline,
          the former is used for non-recent files and the latter for
          recent files; if you want output columns to line up, you may
          need to insert spaces in one of the two formats.

    `full-iso'
          List timestamps in full using ISO 8601 date, time, and time
          zone format with nanosecond precision, e.g., `2002-03-30
          23:45:56.477817180 -0700'.  This style is equivalent to
          `+%Y-%m-%d %H:%M:%S.%N %z'.

          This is useful because the time output includes all the
          information that is available from the operating system.  For
          example, this can help explain `make''s behavior, since GNU
          `make' uses the full timestamp to determine whether a file is
          out of date.

    `long-iso'
          List ISO 8601 date and time in minutes, e.g., `2002-03-30
          23:45'.  These timestamps are shorter than `full-iso'
          timestamps, and are usually good enough for everyday work.
          This style is equivalent to `+%Y-%m-%d %H:%M'.

    `iso'
          List ISO 8601 dates for non-recent timestamps (e.g.,
          `2002-03-30 '), and ISO 8601 month, day, hour, and minute for
          recent timestamps (e.g., `03-30 23:45').  These timestamps
          are uglier than `long-iso' timestamps, but they carry nearly
          the same information in a smaller space and their brevity
          helps `ls' output fit within traditional 80-column output
          lines.  The following two `ls' invocations are equivalent:

               newline='
               '
               ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
               ls -l --time-style="iso"

    `locale'
          List timestamps in a locale-dependent form.  For example, a
          Finnish locale might list non-recent timestamps like `maalis
          30  2002' and recent timestamps like `maalis 30 23:45'.
          Locale-dependent timestamps typically consume more space than
          `iso' timestamps and are harder for programs to parse because
          locale conventions vary so widely, but they are easier for
          many people to read.

          The `LC_TIME' locale category specifies the timestamp format.
          The default POSIX locale uses timestamps like `Mar 30  2002'
          and `Mar 30 23:45'; in this locale, the following two `ls'
          invocations are equivalent:

               newline='
               '
               ls -l --time-style="+%b %e  %Y$newline%b %e %H:%M"
               ls -l --time-style="locale"

          Other locales behave differently.  For example, in a German
          locale, `--time-style="locale"' might be equivalent to
          `--time-style="+%e. %b %Y $newline%e. %b %H:%M"' and might
          generate timestamps like `30. Ma"r 2002 ' and `30. Ma"r
          23:45'.

    `posix-STYLE'
          List POSIX-locale timestamps if the `LC_TIME' locale category
          is POSIX, STYLE timestamps otherwise.  For example, the
          `posix-long-iso' style lists timestamps like `Mar 30  2002'
          and `Mar 30 23:45' when in the POSIX locale, and like
          `2002-03-30 23:45' otherwise.

   You can specify the default value of the `--time-style' option with
the environment variable `TIME_STYLE'; if `TIME_STYLE' is not set the
default style is `locale'.  GNU Emacs 21.3 and later use the `--dired'
option and therefore can parse any date format, but if you are using
Emacs 21.1 or 21.2 and specify a non-POSIX locale you may need to set
`TIME_STYLE="posix-long-iso"'.

   To avoid certain denial-of-service attacks, timestamps that would be
longer than 1000 bytes may be treated as errors.

File: coreutils.info,  Node: Formatting the file names,  Prev: Formatting file timestamps,  Up: ls invocation

10.1.7 Formatting the file names
--------------------------------

These options change how file names themselves are printed.

`-b'
`--escape'
`--quoting-style=escape'
     Quote nongraphic characters in file names using alphabetic and
     octal backslash sequences like those used in C.

`-N'
`--literal'
`--quoting-style=literal'
     Do not quote file names.  However, with `ls' nongraphic characters
     are still printed as question marks if the output is a terminal
     and you do not specify the `--show-control-chars' option.

`-q'
`--hide-control-chars'
     Print question marks instead of nongraphic characters in file
     names.  This is the default if the output is a terminal and the
     program is `ls'.

`-Q'
`--quote-name'
`--quoting-style=c'
     Enclose file names in double quotes and quote nongraphic
     characters as in C.

`--quoting-style=WORD'
     Use style WORD to quote file names and other strings that may
     contain arbitrary characters.  The WORD should be one of the
     following:

    `literal'
          Output strings as-is; this is the same as the `-N' or
          `--literal' option.

    `shell'
          Quote strings for the shell if they contain shell
          metacharacters or would cause ambiguous output.  The quoting
          is suitable for POSIX-compatible shells like `bash', but it
          does not always work for incompatible shells like `csh'.

    `shell-always'
          Quote strings for the shell, even if they would normally not
          require quoting.

    `c'
          Quote strings as for C character string literals, including
          the surrounding double-quote characters; this is the same as
          the `-Q' or `--quote-name' option.

    `escape'
          Quote strings as for C character string literals, except omit
          the surrounding double-quote characters; this is the same as
          the `-b' or `--escape' option.

    `clocale'
          Quote strings as for C character string literals, except use
          surrounding quotation marks appropriate for the locale.

    `locale'
          Quote strings as for C character string literals, except use
          surrounding quotation marks appropriate for the locale, and
          quote `like this' instead of "like this" in the default C
          locale.  This looks nicer on many displays.

     You can specify the default value of the `--quoting-style' option
     with the environment variable `QUOTING_STYLE'.  If that environment
     variable is not set, the default value is `literal', but this
     default may change to `shell' in a future version of this package.

`--show-control-chars'
     Print nongraphic characters as-is in file names.  This is the
     default unless the output is a terminal and the program is `ls'.


File: coreutils.info,  Node: dir invocation,  Next: vdir invocation,  Prev: ls invocation,  Up: Directory listing

10.2 `dir': Briefly list directory contents
===========================================

`dir' is equivalent to `ls -C -b'; that is, by default files are listed
in columns, sorted vertically, and special characters are represented
by backslash escape sequences.

   *Note `ls': ls invocation.

File: coreutils.info,  Node: vdir invocation,  Next: dircolors invocation,  Prev: dir invocation,  Up: Directory listing

10.3 `vdir': Verbosely list directory contents
==============================================

`vdir' is equivalent to `ls -l -b'; that is, by default files are
listed in long format and special characters are represented by
backslash escape sequences.

File: coreutils.info,  Node: dircolors invocation,  Prev: vdir invocation,  Up: Directory listing

10.4 `dircolors': Color setup for `ls'
======================================

`dircolors' outputs a sequence of shell commands to set up the terminal
for color output from `ls' (and `dir', etc.).  Typical usage:

     eval "`dircolors [OPTION]... [FILE]`"

   If FILE is specified, `dircolors' reads it to determine which colors
to use for which file types and extensions.  Otherwise, a precompiled
database is used.  For details on the format of these files, run
`dircolors --print-database'.

   To make `dircolors' read a `~/.dircolors' file if it exists, you can
put the following lines in your `~/.bashrc' (or adapt them to your
favorite shell):

     d=.dircolors
     test -r $d && eval "$(dircolors $d)"

   The output is a shell command to set the `LS_COLORS' environment
variable.  You can specify the shell syntax to use on the command line,
or `dircolors' will guess it from the value of the `SHELL' environment
variable.

   The program accepts the following options.  Also see *note Common
options::.

`-b'
`--sh'
`--bourne-shell'
     Output Bourne shell commands.  This is the default if the `SHELL'
     environment variable is set and does not end with `csh' or `tcsh'.

`-c'
`--csh'
`--c-shell'
     Output C shell commands.  This is the default if `SHELL' ends with
     `csh' or `tcsh'.

`-p'
`--print-database'
     Print the (compiled-in) default color configuration database.  This
     output is itself a valid configuration file, and is fairly
     descriptive of the possibilities.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: Basic operations,  Next: Special file types,  Prev: Directory listing,  Up: Top

11 Basic operations
*******************

This chapter describes the commands for basic file manipulation:
copying, moving (renaming), and deleting (removing).

* Menu:

* cp invocation::               Copy files.
* dd invocation::               Convert and copy a file.
* install invocation::          Copy files and set attributes.
* mv invocation::               Move (rename) files.
* rm invocation::               Remove files or directories.
* shred invocation::            Remove files more securely.

File: coreutils.info,  Node: cp invocation,  Next: dd invocation,  Up: Basic operations

11.1 `cp': Copy files and directories
=====================================

`cp' copies files (or, optionally, directories).  The copy is
completely independent of the original.  You can either copy one file to
another, or copy arbitrarily many files to a destination directory.
Synopses:

     cp [OPTION]... [-T] SOURCE DEST
     cp [OPTION]... SOURCE... DIRECTORY
     cp [OPTION]... -t DIRECTORY SOURCE...

   * If two file names are given, `cp' copies the first file to the
     second.

   * If the `--target-directory' (`-t') option is given, or failing
     that if the last file is a directory and the
     `--no-target-directory' (`-T') option is not given, `cp' copies
     each SOURCE file to the specified directory, using the SOURCEs'
     names.

   Generally, files are written just as they are read.  For exceptions,
see the `--sparse' option below.

   By default, `cp' does not copy directories.  However, the `-R',
`-a', and `-r' options cause `cp' to copy recursively by descending
into source directories and copying files to corresponding destination
directories.

   When copying from a symbolic link, `cp' normally follows the link
only when not copying recursively.  This default can be overridden with
the `--archive' (`-a'), `-d', `--dereference' (`-L'),
`--no-dereference' (`-P'), and `-H' options.  If more than one of these
options is specified, the last one silently overrides the others.

   When copying to a symbolic link, `cp' follows the link only when it
refers to an existing regular file.  However, when copying to a
dangling symbolic link, `cp' refuses by default, and fails with a
diagnostic, since the operation is inherently dangerous.  This behavior
is contrary to historical practice and to POSIX.  Set `POSIXLY_CORRECT'
to make `cp' attempt to create the target of a dangling destination
symlink, in spite of the possible risk.  Also, when an option like
`--backup' or `--link' acts to rename or remove the destination before
copying, `cp' renames or removes the symbolic link rather than the file
it points to.

   By default, `cp' copies the contents of special files only when not
copying recursively.  This default can be overridden with the
`--copy-contents' option.

   `cp' generally refuses to copy a file onto itself, with the
following exception: if `--force --backup' is specified with SOURCE and
DEST identical, and referring to a regular file, `cp' will make a
backup file, either regular or numbered, as specified in the usual ways
(*note Backup options::).  This is useful when you simply want to make
a backup of an existing file before changing it.

   The program accepts the following options.  Also see *note Common
options::.

`-a'
`--archive'
     Preserve as much as possible of the structure and attributes of the
     original files in the copy (but do not attempt to preserve internal
     directory structure; i.e., `ls -U' may list the entries in a copied
     directory in a different order).  Try to preserve SELinux security
     context and extended attributes (xattr), but ignore any failure to
     do that and print no corresponding diagnostic.  Equivalent to `-dR
     --preserve=all' with the reduced diagnostics.

`-b'
`--backup[=METHOD]'
     *Note Backup options::.  Make a backup of each file that would
     otherwise be overwritten or removed.  As a special case, `cp'
     makes a backup of SOURCE when the force and backup options are
     given and SOURCE and DEST are the same name for an existing,
     regular file.  One useful application of this combination of
     options is this tiny Bourne shell script:

          #!/bin/sh
          # Usage: backup FILE...
          # Create a GNU-style backup of each listed FILE.
          for i; do
            cp --backup --force -- "$i" "$i"
          done

`-c'
     Preserve SELinux security context of the original files if
     possible.  Some file systems don't support storing of SELinux
     security context.

`--copy-contents'
     If copying recursively, copy the contents of any special files
     (e.g., FIFOs and device files) as if they were regular files.
     This means trying to read the data in each source file and writing
     it to the destination.  It is usually a mistake to use this
     option, as it normally has undesirable effects on special files
     like FIFOs and the ones typically found in the `/dev' directory.
     In most cases, `cp -R --copy-contents' will hang indefinitely
     trying to read from FIFOs and special files like `/dev/console',
     and it will fill up your destination disk if you use it to copy
     `/dev/zero'.  This option has no effect unless copying
     recursively, and it does not affect the copying of symbolic links.

`-d'
     Copy symbolic links as symbolic links rather than copying the
     files that they point to, and preserve hard links between source
     files in the copies.  Equivalent to `--no-dereference
     --preserve=links'.

`-f'
`--force'
     When copying without this option and an existing destination file
     cannot be opened for writing, the copy fails.  However, with
     `--force'), when a destination file cannot be opened, `cp' then
     removes it and tries to open it again.  Contrast this behavior
     with that enabled by `--link' and `--symbolic-link', whereby the
     destination file is never opened but rather is removed
     unconditionally.  Also see the description of
     `--remove-destination'.

     This option is independent of the `--interactive' or `-i' option:
     neither cancels the effect of the other.

     This option is redundant if the `--no-clobber' or `-n' option is
     used.

`-H'
     If a command line argument specifies a symbolic link, then copy the
     file it points to rather than the symbolic link itself.  However,
     copy (preserving its nature) any symbolic link that is encountered
     via recursive traversal.

`-i'
`--interactive'
     When copying a file other than a directory, prompt whether to
     overwrite an existing destination file. The `-i' option overrides
     a previous `-n' option.

`-l'
`--link'
     Make hard links instead of copies of non-directories.

`-L'
`--dereference'
     Follow symbolic links when copying from them.  With this option,
     `cp' cannot create a symbolic link.  For example, a symlink (to
     regular file) in the source tree will be copied to a regular file
     in the destination tree.

`-n'
`--no-clobber'
     Do not overwrite an existing file. The `-n' option overrides a
     previous `-i' option. This option is mutually exclusive with `-b'
     or `--backup' option.

`-P'
`--no-dereference'
     Copy symbolic links as symbolic links rather than copying the
     files that they point to.  This option affects only symbolic links
     in the source; symbolic links in the destination are always
     followed if possible.

`-p'
`--preserve[=ATTRIBUTE_LIST]'
     Preserve the specified attributes of the original files.  If
     specified, the ATTRIBUTE_LIST must be a comma-separated list of
     one or more of the following strings:

    `mode'
          Preserve the file mode bits and access control lists.

    `ownership'
          Preserve the owner and group.  On most modern systems, only
          users with appropriate privileges may change the owner of a
          file, and ordinary users may preserve the group ownership of
          a file only if they happen to be a member of the desired
          group.

    `timestamps'
          Preserve the times of last access and last modification, when
          possible.  On older systems, it is not possible to preserve
          these attributes when the affected file is a symbolic link.
          However, many systems now provide the `utimensat' function,
          which makes it possible even for symbolic links.

    `links'
          Preserve in the destination files any links between
          corresponding source files.  Note that with `-L' or `-H',
          this option can convert symbolic links to hard links.  For
          example,
               $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
               74161745 a
               74161745 b
          Note the inputs: `b' is a symlink to regular file `a', yet
          the files in destination directory, `c/', are hard-linked.
          Since `-a' implies `--preserve=links', and since `-H' tells
          `cp' to dereference command line arguments, it sees two files
          with the same inode number, and preserves the perceived hard
          link.

          Here is a similar example that exercises `cp''s `-L' option:
               $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
               74163295 a
               74163295 b

    `context'
          Preserve SELinux security context of the file. `cp' will fail
          if the preserving of SELinux security context is not
          succesful.

    `xattr'
          Preserve extended attributes if `cp' is built with xattr
          support, and xattrs are supported and enabled on your file
          system.  If SELinux context and/or ACLs are implemented using
          xattrs, they are preserved by this option as well.

    `all'
          Preserve all file attributes.  Equivalent to specifying all
          of the above, but with the difference that failure to
          preserve SELinux security context or extended attributes does
          not change `cp''s exit status.  `cp' does diagnose such
          failures.

     Using `--preserve' with no ATTRIBUTE_LIST is equivalent to
     `--preserve=mode,ownership,timestamps'.

     In the absence of this option, each destination file is created
     with the mode bits of the corresponding source file, minus the
     bits set in the umask and minus the set-user-ID and set-group-ID
     bits.  *Note File permissions::.

`--no-preserve=ATTRIBUTE_LIST'
     Do not preserve the specified attributes.  The ATTRIBUTE_LIST has
     the same form as for `--preserve'.

`--parents'
     Form the name of each destination file by appending to the target
     directory a slash and the specified name of the source file.  The
     last argument given to `cp' must be the name of an existing
     directory.  For example, the command:

          cp --parents a/b/c existing_dir

     copies the file `a/b/c' to `existing_dir/a/b/c', creating any
     missing intermediate directories.

`-R'
`-r'
`--recursive'
     Copy directories recursively.  By default, do not follow symbolic
     links in the source; see the `--archive' (`-a'), `-d',
     `--dereference' (`-L'), `--no-dereference' (`-P'), and `-H'
     options.  Special files are copied by creating a destination file
     of the same type as the source; see the `--copy-contents' option.
     It is not portable to use `-r' to copy symbolic links or special
     files.  On some non-GNU systems, `-r' implies the equivalent of
     `-L' and `--copy-contents' for historical reasons.  Also, it is
     not portable to use `-R' to copy symbolic links unless you also
     specify `-P', as POSIX allows implementations that dereference
     symbolic links by default.

`--reflink[=WHEN]'
     Perform a lightweight, copy-on-write (COW) copy.  Copying with
     this option can succeed only on some file systems.  Once it has
     succeeded, beware that the source and destination files share the
     same disk data blocks as long as they remain unmodified.  Thus, if
     a disk I/O error affects data blocks of one of the files, the
     other suffers the exact same fate.

     The WHEN value can be one of the following:

    `always'
          The default behavior: if the copy-on-write operation is not
          supported then report the failure for each file and exit with
          a failure status.

    `auto'
          If the copy-on-write operation is not supported then fall back
          to the standard copy behaviour.

`--remove-destination'
     Remove each existing destination file before attempting to open it
     (contrast with `-f' above).

`--sparse=WHEN'
     A "sparse file" contains "holes"--a sequence of zero bytes that
     does not occupy any physical disk blocks; the `read' system call
     reads these as zeros.  This can both save considerable disk space
     and increase speed, since many binary files contain lots of
     consecutive zero bytes.  By default, `cp' detects holes in input
     source files via a crude heuristic and makes the corresponding
     output file sparse as well.  Only regular files may be sparse.

     The WHEN value can be one of the following:

    `auto'
          The default behavior: if the input file is sparse, attempt to
          make the output file sparse, too.  However, if an output file
          exists but refers to a non-regular file, then do not attempt
          to make it sparse.

    `always'
          For each sufficiently long sequence of zero bytes in the
          input file, attempt to create a corresponding hole in the
          output file, even if the input file does not appear to be
          sparse.  This is useful when the input file resides on a file
          system that does not support sparse files (for example,
          `efs' file systems in SGI IRIX 5.3 and earlier), but the
          output file is on a type of file system that does support
          them.  Holes may be created only in regular files, so if the
          destination file is of some other type, `cp' does not even
          try to make it sparse.

    `never'
          Never make the output file sparse.  This is useful in
          creating a file for use with the `mkswap' command, since such
          a file must not have any holes.

`--strip-trailing-slashes'
     Remove any trailing slashes from each SOURCE argument.  *Note
     Trailing slashes::.

`-s'
`--symbolic-link'
     Make symbolic links instead of copies of non-directories.  All
     source file names must be absolute (starting with `/') unless the
     destination files are in the current directory.  This option merely
     results in an error message on systems that do not support
     symbolic links.

`-S SUFFIX'
`--suffix=SUFFIX'
     Append SUFFIX to each backup file made with `-b'.  *Note Backup
     options::.

`-t DIRECTORY'
`--target-directory=DIRECTORY'
     Specify the destination DIRECTORY.  *Note Target directory::.

`-T'
`--no-target-directory'
     Do not treat the last operand specially when it is a directory or a
     symbolic link to a directory.  *Note Target directory::.

`-u'
`--update'
     Do not copy a non-directory that has an existing destination with
     the same or newer modification time.  If time stamps are being
     preserved, the comparison is to the source time stamp truncated to
     the resolutions of the destination file system and of the system
     calls used to update time stamps; this avoids duplicate work if
     several `cp -pu' commands are executed with the same source and
     destination.

`-v'
`--verbose'
     Print the name of each file before copying it.

`-x'
`--one-file-system'
     Skip subdirectories that are on different file systems from the
     one that the copy started on.  However, mount point directories
     _are_ copied.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: dd invocation,  Next: install invocation,  Prev: cp invocation,  Up: Basic operations

11.2 `dd': Convert and copy a file
==================================

`dd' copies a file (from standard input to standard output, by default)
with a changeable I/O block size, while optionally performing
conversions on it.  Synopses:

     dd [OPERAND]...
     dd OPTION

   The only options are `--help' and `--version'.  *Note Common
options::.  `dd' accepts the following operands.

`if=FILE'
     Read from FILE instead of standard input.

`of=FILE'
     Write to FILE instead of standard output.  Unless `conv=notrunc'
     is given, `dd' truncates FILE to zero bytes (or the size specified
     with `seek=').

`ibs=BYTES'
     Set the input block size to BYTES.  This makes `dd' read BYTES per
     block.  The default is 512 bytes.

`obs=BYTES'
     Set the output block size to BYTES.  This makes `dd' write BYTES
     per block.  The default is 512 bytes.

`bs=BYTES'
     Set both input and output block sizes to BYTES.  This makes `dd'
     read and write BYTES per block, overriding any `ibs' and `obs'
     settings.  In addition, if no data-transforming `conv' option is
     specified, each input block is copied to the output as a single
     block, without aggregating short reads.

`cbs=BYTES'
     Set the conversion block size to BYTES.  When converting
     variable-length records to fixed-length ones (`conv=block') or the
     reverse (`conv=unblock'), use BYTES as the fixed record length.

`skip=BLOCKS'
     Skip BLOCKS `ibs'-byte blocks in the input file before copying.

`seek=BLOCKS'
     Skip BLOCKS `obs'-byte blocks in the output file before copying.

`count=N'
     Copy N `ibs'-byte blocks from the input file, instead of
     everything until the end of the file.  if `iflag=count_bytes' is
     specified, N is interpreted as a byte count rather than a block
     count.

`status=WHICH'
     Transfer information is normally output to stderr upon receipt of
     the `INFO' signal or when `dd' exits.  Specifying WHICH will
     identify which information to suppress.

    `noxfer'
          Do not print the transfer rate and volume statistics that
          normally make up the last status line.

    `none'
          Do not print any informational messages to stderr.  Error
          messages are output as normal.


`conv=CONVERSION[,CONVERSION]...'
     Convert the file as specified by the CONVERSION argument(s).  (No
     spaces around any comma(s).)

     Conversions:

    `ascii'
          Convert EBCDIC to ASCII, using the conversion table specified
          by POSIX.  This provides a 1:1 translation for all 256 bytes.

    `ebcdic'
          Convert ASCII to EBCDIC.  This is the inverse of the `ascii'
          conversion.

    `ibm'
          Convert ASCII to alternate EBCDIC, using the alternate
          conversion table specified by POSIX.  This is not a 1:1
          translation, but reflects common historical practice for `~',
          `[', and `]'.

          The `ascii', `ebcdic', and `ibm' conversions are mutually
          exclusive.

    `block'
          For each line in the input, output `cbs' bytes, replacing the
          input newline with a space and padding with spaces as
          necessary.

    `unblock'
          Remove any trailing spaces in each `cbs'-sized input block,
          and append a newline.

          The `block' and `unblock' conversions are mutually exclusive.

    `lcase'
          Change uppercase letters to lowercase.

    `ucase'
          Change lowercase letters to uppercase.

          The `lcase' and `ucase' conversions are mutually exclusive.

    `sparse'
          Try to seek rather than write NUL output blocks.  On a file
          system that supports sparse files, this will create sparse
          output when extending the output file.  Be careful when using
          this option in conjunction with `conv=notrunc' or
          `oflag=append'.  With `conv=notrunc', existing data in the
          output corresponding to NUL blocks from the input, will be
          untouched.  With `oflag=append' the seeks performed will be
          ineffective.

    `swab'
          Swap every pair of input bytes.  GNU `dd', unlike others,
          works when an odd number of bytes are read--the last byte is
          simply copied (since there is nothing to swap it with).

    `noerror'
          Continue after read errors.

    `nocreat'
          Do not create the output file; the output file must already
          exist.

    `excl'
          Fail if the output file already exists; `dd' must create the
          output file itself.

          The `excl' and `nocreat' conversions are mutually exclusive.

    `notrunc'
          Do not truncate the output file.

    `sync'
          Pad every input block to size of `ibs' with trailing zero
          bytes.  When used with `block' or `unblock', pad with spaces
          instead of zero bytes.

    `fdatasync'
          Synchronize output data just before finishing.  This forces a
          physical write of output data.

    `fsync'
          Synchronize output data and metadata just before finishing.
          This forces a physical write of output data and metadata.


`iflag=FLAG[,FLAG]...'
     Access the input file using the flags specified by the FLAG
     argument(s).  (No spaces around any comma(s).)

`oflag=FLAG[,FLAG]...'
     Access the output file using the flags specified by the FLAG
     argument(s).  (No spaces around any comma(s).)

     Here are the flags.  Not every flag is supported on every operating
     system.

    `append'
          Write in append mode, so that even if some other process is
          writing to this file, every `dd' write will append to the
          current contents of the file.  This flag makes sense only for
          output.  If you combine this flag with the `of=FILE' operand,
          you should also specify `conv=notrunc' unless you want the
          output file to be truncated before being appended to.

    `cio'
          Use concurrent I/O mode for data.  This mode performs direct
          I/O and drops the POSIX requirement to serialize all I/O to
          the same file.  A file cannot be opened in CIO mode and with
          a standard open at the same time.

    `direct'
          Use direct I/O for data, avoiding the buffer cache.  Note
          that the kernel may impose restrictions on read or write
          buffer sizes.  For example, with an ext4 destination file
          system and a linux-based kernel, using `oflag=direct' will
          cause writes to fail with `EINVAL' if the output buffer size
          is not a multiple of 512.  Note that this flag is turned off
          automatically when a partial block is written, which happens
          when reading from a pipe and not re-blocking.  You can
          prevent that by using `iflag=fullblock'.

    `directory'
          Fail unless the file is a directory.  Most operating systems
          do not allow I/O to a directory, so this flag has limited
          utility.

    `dsync'
          Use synchronized I/O for data.  For the output file, this
          forces a physical write of output data on each write.  For
          the input file, this flag can matter when reading from a
          remote file that has been written to synchronously by some
          other process.  Metadata (e.g., last-access and last-modified
          time) is not necessarily synchronized.

    `sync'
          Use synchronized I/O for both data and metadata.

    `nonblock'
          Use non-blocking I/O.

    `noatime'
          Do not update the file's access time.  Some older file
          systems silently ignore this flag, so it is a good idea to
          test it on your files before relying on it.

    `noctty'
          Do not assign the file to be a controlling terminal for `dd'.
          This has no effect when the file is not a terminal.  On many
          hosts (e.g., GNU/Linux hosts), this option has no effect at
          all.

    `nofollow'
          Do not follow symbolic links.

    `nolinks'
          Fail if the file has multiple hard links.

    `binary'
          Use binary I/O.  This option has an effect only on nonstandard
          platforms that distinguish binary from text I/O.

    `text'
          Use text I/O.  Like `binary', this option has no effect on
          standard platforms.

    `fullblock'
          Accumulate full blocks from input.  The `read' system call
          may return early if a full block is not available.  When that
          happens, continue calling `read' to fill the remainder of the
          block.  This flag can be used only with `iflag'.

    `count_bytes'
          Interpret the `count=' operand as a byte count, rather than a
          block count, which allows specifying a length that is not a
          multiple of the I/O block size.  This flag can be used only
          with `iflag'.


     These flags are not supported on all systems, and `dd' rejects
     attempts to use them when they are not supported.  When reading
     from standard input or writing to standard output, the `nofollow'
     and `noctty' flags should not be specified, and the other flags
     (e.g., `nonblock') can affect how other processes behave with the
     affected file descriptors, even after `dd' exits.


   The numeric-valued strings above (BYTES and BLOCKS) can be followed
by a multiplier: `b'=512, `c'=1, `w'=2, `xM'=M, or any of the standard
block size suffixes like `k'=1024 (*note Block size::).

   Use different `dd' invocations to use different block sizes for
skipping and I/O.  For example, the following shell commands copy data
in 512 KiB blocks between a disk and a tape, but do not save or restore
a 4 KiB label at the start of the disk:

     disk=/dev/rdsk/c0t1d0s2
     tape=/dev/rmt/0

     # Copy all but the label from disk to tape.
     (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape

     # Copy from tape back to disk, but leave the disk label alone.
     (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk

   Sending an `INFO' signal to a running `dd' process makes it print
I/O statistics to standard error and then resume copying.  In the
example below, `dd' is run in the background to copy 10 million blocks.
The `kill' command makes it output intermediate I/O statistics, and
when `dd' completes normally or is killed by the `SIGINT' signal, it
outputs the final statistics.

     $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
     $ kill -s INFO $pid; wait $pid
     3385223+0 records in
     3385223+0 records out
     1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
     10000000+0 records in
     10000000+0 records out
     5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s

   On systems lacking the `INFO' signal `dd' responds to the `USR1'
signal instead, unless the `POSIXLY_CORRECT' environment variable is
set.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: install invocation,  Next: mv invocation,  Prev: dd invocation,  Up: Basic operations

11.3 `install': Copy files and set attributes
=============================================

`install' copies files while setting their file mode bits and, if
possible, their owner and group.  Synopses:

     install [OPTION]... [-T] SOURCE DEST
     install [OPTION]... SOURCE... DIRECTORY
     install [OPTION]... -t DIRECTORY SOURCE...
     install [OPTION]... -d DIRECTORY...

   * If two file names are given, `install' copies the first file to the
     second.

   * If the `--target-directory' (`-t') option is given, or failing
     that if the last file is a directory and the
     `--no-target-directory' (`-T') option is not given, `install'
     copies each SOURCE file to the specified directory, using the
     SOURCEs' names.

   * If the `--directory' (`-d') option is given, `install' creates
     each DIRECTORY and any missing parent directories.  Parent
     directories are created with mode `u=rwx,go=rx' (755), regardless
     of the `-m' option or the current umask.  *Note Directory Setuid
     and Setgid::, for how the set-user-ID and set-group-ID bits of
     parent directories are inherited.

   `install' is similar to `cp', but allows you to control the
attributes of destination files.  It is typically used in Makefiles to
copy programs into their destination directories.  It refuses to copy
files onto themselves.

   `install' never preserves extended attributes (xattr).

   The program accepts the following options.  Also see *note Common
options::.

`-b'
`--backup[=METHOD]'
     *Note Backup options::.  Make a backup of each file that would
     otherwise be overwritten or removed.

`-C'
`--compare'
     Compare each pair of source and destination files, and if the
     destination has identical content and any specified owner, group,
     permissions, and possibly SELinux context, then do not modify the
     destination at all.

`-c'
     Ignored; for compatibility with old Unix versions of `install'.

`-D'
     Create any missing parent directories of DEST, then copy SOURCE to
     DEST.  This option is ignored if a destination directory is
     specified via `--target-directory=DIR'.

`-d'
`--directory'
     Create any missing parent directories, giving them the default
     attributes.  Then create each given directory, setting their owner,
     group and mode as given on the command line or to the defaults.

`-g GROUP'
`--group=GROUP'
     Set the group ownership of installed files or directories to
     GROUP.  The default is the process's current group.  GROUP may be
     either a group name or a numeric group ID.

`-m MODE'
`--mode=MODE'
     Set the file mode bits for the installed file or directory to MODE,
     which can be either an octal number, or a symbolic mode as in
     `chmod', with `a=' (no access allowed to anyone) as the point of
     departure (*note File permissions::).  The default mode is
     `u=rwx,go=rx,a-s'--read, write, and execute for the owner, read
     and execute for group and other, and with set-user-ID and
     set-group-ID disabled.  This default is not quite the same as
     `755', since it disables instead of preserving set-user-ID and
     set-group-ID on directories.  *Note Directory Setuid and Setgid::.

`-o OWNER'
`--owner=OWNER'
     If `install' has appropriate privileges (is run as root), set the
     ownership of installed files or directories to OWNER.  The default
     is `root'.  OWNER may be either a user name or a numeric user ID.

`--preserve-context'
     Preserve the SELinux security context of files and directories.
     Failure to preserve the context in all of the files or directories
     will result in an exit status of 1.  If SELinux is disabled then
     print a warning and ignore the option.

`-p'
`--preserve-timestamps'
     Set the time of last access and the time of last modification of
     each installed file to match those of each corresponding original
     file.  When a file is installed without this option, its last
     access and last modification times are both set to the time of
     installation.  This option is useful if you want to use the last
     modification times of installed files to keep track of when they
     were last built as opposed to when they were last installed.

`-s'
`--strip'
     Strip the symbol tables from installed binary executables.

`--strip-program=PROGRAM'
     Program used to strip binaries.

`-S SUFFIX'
`--suffix=SUFFIX'
     Append SUFFIX to each backup file made with `-b'.  *Note Backup
     options::.

`-t DIRECTORY'
`--target-directory=DIRECTORY'
     Specify the destination DIRECTORY.  *Note Target directory::.

`-T'
`--no-target-directory'
     Do not treat the last operand specially when it is a directory or a
     symbolic link to a directory.  *Note Target directory::.

`-v'
`--verbose'
     Print the name of each file before copying it.

`-Z CONTEXT'
`--context=CONTEXT'
     Set the default SELinux security context to be used for any
     created files and directories.  If SELinux is disabled then print
     a warning and ignore the option.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: mv invocation,  Next: rm invocation,  Prev: install invocation,  Up: Basic operations

11.4 `mv': Move (rename) files
==============================

`mv' moves or renames files (or directories).  Synopses:

     mv [OPTION]... [-T] SOURCE DEST
     mv [OPTION]... SOURCE... DIRECTORY
     mv [OPTION]... -t DIRECTORY SOURCE...

   * If two file names are given, `mv' moves the first file to the
     second.

   * If the `--target-directory' (`-t') option is given, or failing
     that if the last file is a directory and the
     `--no-target-directory' (`-T') option is not given, `mv' moves
     each SOURCE file to the specified directory, using the SOURCEs'
     names.

   `mv' can move any type of file from one file system to another.
Prior to version `4.0' of the fileutils, `mv' could move only regular
files between file systems.  For example, now `mv' can move an entire
directory hierarchy including special device files from one partition
to another.  It first uses some of the same code that's used by `cp -a'
to copy the requested directories and files, then (assuming the copy
succeeded) it removes the originals.  If the copy fails, then the part
that was copied to the destination partition is removed.  If you were
to copy three directories from one partition to another and the copy of
the first directory succeeded, but the second didn't, the first would
be left on the destination partition and the second and third would be
left on the original partition.

   `mv' always tries to copy extended attributes (xattr).

   If a destination file exists but is normally unwritable, standard
input is a terminal, and the `-f' or `--force' option is not given,
`mv' prompts the user for whether to replace the file.  (You might own
the file, or have write permission on its directory.)  If the response
is not affirmative, the file is skipped.

   _Warning_: Avoid specifying a source name with a trailing slash,
when it might be a symlink to a directory.  Otherwise, `mv' may do
something very surprising, since its behavior depends on the underlying
rename system call.  On a system with a modern Linux-based kernel, it
fails with `errno=ENOTDIR'.  However, on other systems (at least
FreeBSD 6.1 and Solaris 10) it silently renames not the symlink but
rather the directory referenced by the symlink.  *Note Trailing
slashes::.

   The program accepts the following options.  Also see *note Common
options::.

`-b'
`--backup[=METHOD]'
     *Note Backup options::.  Make a backup of each file that would
     otherwise be overwritten or removed.

`-f'
`--force'
     Do not prompt the user before removing a destination file.  If you
     specify more than one of the `-i', `-f', `-n' options, only the
     final one takes effect.

`-i'
`--interactive'
     Prompt whether to overwrite each existing destination file,
     regardless of its permissions.  If the response is not
     affirmative, the file is skipped.  If you specify more than one of
     the `-i', `-f', `-n' options, only the final one takes effect.

`-n'
`--no-clobber'
     Do not overwrite an existing file.  If you specify more than one
     of the `-i', `-f', `-n' options, only the final one takes effect.
     This option is mutually exclusive with `-b' or `--backup' option.

`-u'
`--update'
     Do not move a non-directory that has an existing destination with
     the same or newer modification time.  If the move is across file
     system boundaries, the comparison is to the source time stamp
     truncated to the resolutions of the destination file system and of
     the system calls used to update time stamps; this avoids duplicate
     work if several `mv -u' commands are executed with the same source
     and destination.

`-v'
`--verbose'
     Print the name of each file before moving it.

`--strip-trailing-slashes'
     Remove any trailing slashes from each SOURCE argument.  *Note
     Trailing slashes::.

`-S SUFFIX'
`--suffix=SUFFIX'
     Append SUFFIX to each backup file made with `-b'.  *Note Backup
     options::.

`-t DIRECTORY'
`--target-directory=DIRECTORY'
     Specify the destination DIRECTORY.  *Note Target directory::.

`-T'
`--no-target-directory'
     Do not treat the last operand specially when it is a directory or a
     symbolic link to a directory.  *Note Target directory::.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: rm invocation,  Next: shred invocation,  Prev: mv invocation,  Up: Basic operations

11.5 `rm': Remove files or directories
======================================

`rm' removes each given FILE.  By default, it does not remove
directories.  Synopsis:

     rm [OPTION]... [FILE]...

   If the `-I' or `--interactive=once' option is given, and there are
more than three files or the `-r', `-R', or `--recursive' are given,
then `rm' prompts the user for whether to proceed with the entire
operation.  If the response is not affirmative, the entire command is
aborted.

   Otherwise, if a file is unwritable, standard input is a terminal, and
the `-f' or `--force' option is not given, or the `-i' or
`--interactive=always' option _is_ given, `rm' prompts the user for
whether to remove the file.  If the response is not affirmative, the
file is skipped.

   Any attempt to remove a file whose last file name component is `.'
or `..' is rejected without any prompting.

   _Warning_: If you use `rm' to remove a file, it is usually possible
to recover the contents of that file.  If you want more assurance that
the contents are truly unrecoverable, consider using `shred'.

   The program accepts the following options.  Also see *note Common
options::.

`-f'
`--force'
     Ignore nonexistent files and never prompt the user.  Ignore any
     previous `--interactive' (`-i') option.

`-i'
     Prompt whether to remove each file.  If the response is not
     affirmative, the file is skipped.  Ignore any previous `--force'
     (`-f') option.  Equivalent to `--interactive=always'.

`-I'
     Prompt once whether to proceed with the command, if more than three
     files are named or if a recursive removal is requested.  Ignore any
     previous `--force' (`-f') option.  Equivalent to
     `--interactive=once'.

`--interactive [=WHEN]'
     Specify when to issue an interactive prompt.  WHEN may be omitted,
     or one of:
        * never - Do not prompt at all.

        * once - Prompt once if more than three files are named or if a
          recursive removal is requested.  Equivalent to `-I'.

        * always - Prompt for every file being removed.  Equivalent to
          `-i'.
     `--interactive' with no WHEN is equivalent to
     `--interactive=always'.

`--one-file-system'
     When removing a hierarchy recursively, skip any directory that is
     on a file system different from that of the corresponding command
     line argument.

     This option is useful when removing a build "chroot" hierarchy,
     which normally contains no valuable data.  However, it is not
     uncommon to bind-mount `/home' into such a hierarchy, to make it
     easier to use one's start-up file.  The catch is that it's easy to
     forget to unmount `/home'.  Then, when you use `rm -rf' to remove
     your normally throw-away chroot, that command will remove
     everything under `/home', too.  Use the `--one-file-system'
     option, and it will warn about and skip directories on other file
     systems.  Of course, this will not save your `/home' if it and your
     chroot happen to be on the same file system.

`--preserve-root'
     Fail upon any attempt to remove the root directory, `/', when used
     with the `--recursive' option.  This is the default behavior.
     *Note Treating / specially::.

`--no-preserve-root'
     Do not treat `/' specially when removing recursively.  This option
     is not recommended unless you really want to remove all the files
     on your computer.  *Note Treating / specially::.

`-r'
`-R'
`--recursive'
     Remove the listed directories and their contents recursively.

`-v'
`--verbose'
     Print the name of each file before removing it.


   One common question is how to remove files whose names begin with a
`-'.  GNU `rm', like every program that uses the `getopt' function to
parse its arguments, lets you use the `--' option to indicate that all
following arguments are non-options.  To remove a file called `-f' in
the current directory, you could type either:

     rm -- -f

or:

     rm ./-f

   The Unix `rm' program's use of a single `-' for this purpose
predates the development of the getopt standard syntax.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: shred invocation,  Prev: rm invocation,  Up: Basic operations

11.6 `shred': Remove files more securely
========================================

`shred' overwrites devices or files, to help prevent even very
expensive hardware from recovering the data.

   Ordinarily when you remove a file (*note rm invocation::), the data
is not actually destroyed.  Only the index listing where the file is
stored is destroyed, and the storage is made available for reuse.
There are undelete utilities that will attempt to reconstruct the index
and can bring the file back if the parts were not reused.

   On a busy system with a nearly-full drive, space can get reused in a
few seconds.  But there is no way to know for sure.  If you have
sensitive data, you may want to be sure that recovery is not possible
by actually overwriting the file with non-sensitive data.

   However, even after doing that, it is possible to take the disk back
to a laboratory and use a lot of sensitive (and expensive) equipment to
look for the faint "echoes" of the original data underneath the
overwritten data.  If the data has only been overwritten once, it's not
even that hard.

   The best way to remove something irretrievably is to destroy the
media it's on with acid, melt it down, or the like.  For cheap
removable media like floppy disks, this is the preferred method.
However, hard drives are expensive and hard to melt, so the `shred'
utility tries to achieve a similar effect non-destructively.

   This uses many overwrite passes, with the data patterns chosen to
maximize the damage they do to the old data.  While this will work on
floppies, the patterns are designed for best effect on hard drives.
For more details, see the source code and Peter Gutmann's paper `Secure
Deletion of Data from Magnetic and Solid-State Memory'
(http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html), from the
proceedings of the Sixth USENIX Security Symposium (San Jose,
California, July 22-25, 1996).

   *Please note* that `shred' relies on a very important assumption:
that the file system overwrites data in place.  This is the traditional
way to do things, but many modern file system designs do not satisfy
this assumption.  Exceptions include:

   * Log-structured or journaled file systems, such as those supplied
     with AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in
     `data=journal' mode), BFS, NTFS, etc. when they are configured to
     journal _data_.

   * File systems that write redundant data and carry on even if some
     writes fail, such as RAID-based file systems.

   * File systems that make snapshots, such as Network Appliance's NFS
     server.

   * File systems that cache in temporary locations, such as NFS
     version 3 clients.

   * Compressed file systems.

   In the particular case of ext3 file systems, the above disclaimer
applies (and `shred' is thus of limited effectiveness) only in
`data=journal' mode, which journals file data in addition to just
metadata. In both the `data=ordered' (default) and `data=writeback'
modes, `shred' works as usual.  Ext3 journaling modes can be changed by
adding the `data=something' option to the mount options for a
particular file system in the `/etc/fstab' file, as documented in the
mount man page (man mount).

   If you are not sure how your file system operates, then you should
assume that it does not overwrite data in place, which means that shred
cannot reliably operate on regular files in your file system.

   Generally speaking, it is more reliable to shred a device than a
file, since this bypasses the problem of file system design mentioned
above.  However, even shredding devices is not always completely
reliable.  For example, most disks map out bad sectors invisibly to the
application; if the bad sectors contain sensitive data, `shred' won't
be able to destroy it.

   `shred' makes no attempt to detect or report this problem, just as
it makes no attempt to do anything about backups.  However, since it is
more reliable to shred devices than files, `shred' by default does not
truncate or remove the output file.  This default is more suitable for
devices, which typically cannot be truncated and should not be removed.

   Finally, consider the risk of backups and mirrors.  File system
backups and remote mirrors may contain copies of the file that cannot
be removed, and that will allow a shredded file to be recovered later.
So if you keep any data you may later want to destroy using `shred', be
sure that it is not backed up or mirrored.

     shred [OPTION]... FILE[...]

   The program accepts the following options.  Also see *note Common
options::.

`-f'
`--force'
     Override file permissions if necessary to allow overwriting.

`-NUMBER'
`-n NUMBER'
`--iterations=NUMBER'
     By default, `shred' uses 3 passes of overwrite. You can reduce
     this to save time, or increase it if you think it's appropriate.
     After 25 passes all of the internal overwrite patterns will have
     been used at least once.

`--random-source=FILE'
     Use FILE as a source of random data used to overwrite and to
     choose pass ordering.  *Note Random sources::.

`-s BYTES'
`--size=BYTES'
     Shred the first BYTES bytes of the file.  The default is to shred
     the whole file.  BYTES can be followed by a size specification like
     `K', `M', or `G' to specify a multiple.  *Note Block size::.

`-u'
`--remove'
     After shredding a file, truncate it (if possible) and then remove
     it.  If a file has multiple links, only the named links will be
     removed.

`-v'
`--verbose'
     Display to standard error all status updates as sterilization
     proceeds.

`-x'
`--exact'
     By default, `shred' rounds the size of a regular file up to the
     next multiple of the file system block size to fully erase the
     last block of the file.  Use `--exact' to suppress that behavior.
     Thus, by default if you shred a 10-byte regular file on a system
     with 512-byte blocks, the resulting file will be 512 bytes long.
     With this option, shred does not increase the apparent size of the
     file.

`-z'
`--zero'
     Normally, the last pass that `shred' writes is made up of random
     data.  If this would be conspicuous on your hard drive (for
     example, because it looks like encrypted data), or you just think
     it's tidier, the `--zero' option adds an additional overwrite pass
     with all zero bits.  This is in addition to the number of passes
     specified by the `--iterations' option.


   You might use the following command to erase all trace of the file
system you'd created on the floppy disk in your first drive.  That
command takes about 20 minutes to erase a "1.44MB" (actually 1440 KiB)
floppy.

     shred --verbose /dev/fd0

   Similarly, to erase all data on a selected partition of your hard
disk, you could give a command like this:

     shred --verbose /dev/sda5

   A FILE of `-' denotes standard output.  The intended use of this is
to shred a removed temporary file.  For example:

     i=`tempfile -m 0600`
     exec 3<>"$i"
     rm -- "$i"
     echo "Hello, world" >&3
     shred - >&3
     exec 3>-

   However, the command `shred - >file' does not shred the contents of
FILE, since the shell truncates FILE before invoking `shred'.  Use the
command `shred file' or (if using a Bourne-compatible shell) the
command `shred - 1<>file' instead.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: Special file types,  Next: Changing file attributes,  Prev: Basic operations,  Up: Top

12 Special file types
*********************

This chapter describes commands which create special types of files (and
`rmdir', which removes directories, one special file type).

   Although Unix-like operating systems have markedly fewer special file
types than others, not _everything_ can be treated only as the
undifferentiated byte stream of "normal files".  For example, when a
file is created or removed, the system must record this information,
which it does in a "directory"--a special type of file.  Although you
can read directories as normal files, if you're curious, in order for
the system to do its job it must impose a structure, a certain order,
on the bytes of the file.  Thus it is a "special" type of file.

   Besides directories, other special file types include named pipes
(FIFOs), symbolic links, sockets, and so-called "special files".

* Menu:

* link invocation::             Make a hard link via the link syscall
* ln invocation::               Make links between files.
* mkdir invocation::            Make directories.
* mkfifo invocation::           Make FIFOs (named pipes).
* mknod invocation::            Make block or character special files.
* readlink invocation::         Print value of a symlink or canonical file name.
* rmdir invocation::            Remove empty directories.
* unlink invocation::           Remove files via the unlink syscall

File: coreutils.info,  Node: link invocation,  Next: ln invocation,  Up: Special file types

12.1 `link': Make a hard link via the link syscall
==================================================

`link' creates a single hard link at a time.  It is a minimalist
interface to the system-provided `link' function.  *Note Hard Links:
(libc)Hard Links.  It avoids the bells and whistles of the more
commonly-used `ln' command (*note ln invocation::).  Synopsis:

     link FILENAME LINKNAME

   FILENAME must specify an existing file, and LINKNAME must specify a
nonexistent entry in an existing directory.  `link' simply calls `link
(FILENAME, LINKNAME)' to create the link.

   On a GNU system, this command acts like `ln --directory
--no-target-directory FILENAME LINKNAME'.  However, the `--directory'
and `--no-target-directory' options are not specified by POSIX, and the
`link' command is more portable in practice.

   If FILENAME is a symbolic link, it is unspecified whether LINKNAME
will be a hard link to the symbolic link or to the target of the
symbolic link.  Use `ln -P' or `ln -L' to specify which behavior is
desired.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: ln invocation,  Next: mkdir invocation,  Prev: link invocation,  Up: Special file types

12.2 `ln': Make links between files
===================================

`ln' makes links between files.  By default, it makes hard links; with
the `-s' option, it makes symbolic (or "soft") links.  Synopses:

     ln [OPTION]... [-T] TARGET LINKNAME
     ln [OPTION]... TARGET
     ln [OPTION]... TARGET... DIRECTORY
     ln [OPTION]... -t DIRECTORY TARGET...

   * If two file names are given, `ln' creates a link to the first file
     from the second.

   * If one TARGET is given, `ln' creates a link to that file in the
     current directory.

   * If the `--target-directory' (`-t') option is given, or failing
     that if the last file is a directory and the
     `--no-target-directory' (`-T') option is not given, `ln' creates a
     link to each TARGET file in the specified directory, using the
     TARGETs' names.


   Normally `ln' does not remove existing files.  Use the `--force'
(`-f') option to remove them unconditionally, the `--interactive'
(`-i') option to remove them conditionally, and the `--backup' (`-b')
option to rename them.

   A "hard link" is another name for an existing file; the link and the
original are indistinguishable.  Technically speaking, they share the
same inode, and the inode contains all the information about a
file--indeed, it is not incorrect to say that the inode _is_ the file.
Most systems prohibit making a hard link to a directory; on those where
it is allowed, only the super-user can do so (and with caution, since
creating a cycle will cause problems to many other utilities).  Hard
links cannot cross file system boundaries.  (These restrictions are not
mandated by POSIX, however.)

   "Symbolic links" ("symlinks" for short), on the other hand, are a
special file type (which not all kernels support: System V release 3
(and older) systems lack symlinks) in which the link file actually
refers to a different file, by name.  When most operations (opening,
reading, writing, and so on) are passed the symbolic link file, the
kernel automatically "dereferences" the link and operates on the target
of the link.  But some operations (e.g., removing) work on the link
file itself, rather than on its target.  The owner and group of a
symlink are not significant to file access performed through the link,
but do have implications on deleting a symbolic link from a directory
with the restricted deletion bit set.  On the GNU system, the mode of a
symlink has no significance and cannot be changed, but on some BSD
systems, the mode can be changed and will affect whether the symlink
will be traversed in file name resolution.  *Note Symbolic Links:
(libc)Symbolic Links.

   Symbolic links can contain arbitrary strings; a "dangling symlink"
occurs when the string in the symlink does not resolve to a file.
There are no restrictions against creating dangling symbolic links.
There are trade-offs to using absolute or relative symlinks.  An
absolute symlink always points to the same file, even if the directory
containing the link is moved.  However, if the symlink is visible from
more than one machine (such as on a networked file system), the file
pointed to might not always be the same.  A relative symbolic link is
resolved in relation to the directory that contains the link, and is
often useful in referring to files on the same device without regards
to what name that device is mounted on when accessed via networked
machines.

   When creating a relative symlink in a different location than the
current directory, the resolution of the symlink will be different than
the resolution of the same string from the current directory.
Therefore, many users prefer to first change directories to the
location where the relative symlink will be created, so that
tab-completion or other file resolution will find the same target as
what will be placed in the symlink.

   The program accepts the following options.  Also see *note Common
options::.

`-b'
`--backup[=METHOD]'
     *Note Backup options::.  Make a backup of each file that would
     otherwise be overwritten or removed.

`-d'
`-F'
`--directory'
     Allow users with appropriate privileges to attempt to make hard
     links to directories.  However, note that this will probably fail
     due to system restrictions, even for the super-user.

`-f'
`--force'
     Remove existing destination files.

`-i'
`--interactive'
     Prompt whether to remove existing destination files.

`-L'
`--logical'
     If `-s' is not in effect, and the source file is a symbolic link,
     create the hard link to the file referred to by the symbolic link,
     rather than the symbolic link itself.

`-n'
`--no-dereference'
     Do not treat the last operand specially when it is a symbolic link
     to a directory.  Instead, treat it as if it were a normal file.

     When the destination is an actual directory (not a symlink to one),
     there is no ambiguity.  The link is created in that directory.
     But when the specified destination is a symlink to a directory,
     there are two ways to treat the user's request.  `ln' can treat
     the destination just as it would a normal directory and create the
     link in it.  On the other hand, the destination can be viewed as a
     non-directory--as the symlink itself.  In that case, `ln' must
     delete or backup that symlink before creating the new link.  The
     default is to treat a destination that is a symlink to a directory
     just like a directory.

     This option is weaker than the `--no-target-directory' (`-T')
     option, so it has no effect if both options are given.

`-P'
`--physical'
     If `-s' is not in effect, and the source file is a symbolic link,
     create the hard link to the symbolic link itself.  On platforms
     where this is not supported by the kernel, this option creates a
     symbolic link with identical contents; since symbolic link contents
     cannot be edited, any file name resolution performed through either
     link will be the same as if a hard link had been created.

`-s'
`--symbolic'
     Make symbolic links instead of hard links.  This option merely
     produces an error message on systems that do not support symbolic
     links.

`-S SUFFIX'
`--suffix=SUFFIX'
     Append SUFFIX to each backup file made with `-b'.  *Note Backup
     options::.

`-t DIRECTORY'
`--target-directory=DIRECTORY'
     Specify the destination DIRECTORY.  *Note Target directory::.

`-T'
`--no-target-directory'
     Do not treat the last operand specially when it is a directory or a
     symbolic link to a directory.  *Note Target directory::.

`-v'
`--verbose'
     Print the name of each file after linking it successfully.


   If `-L' and `-P' are both given, the last one takes precedence.  If
`-s' is also given, `-L' and `-P' are silently ignored.  If neither
option is given, then this implementation defaults to `-P' if the
system `link' supports hard links to symbolic links (such as the GNU
system), and `-L' if `link' follows symbolic links (such as on BSD).

   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Examples:

     Bad Example:

     # Create link ../a pointing to a in that directory.
     # Not really useful because it points to itself.
     ln -s a ..

     Better Example:

     # Change to the target before creating symlinks to avoid being confused.
     cd ..
     ln -s adir/a .

     Bad Example:

     # Hard coded file names don't move well.
     ln -s $(pwd)/a /some/dir/

     Better Example:

     # Relative file names survive directory moves and also
     # work across networked file systems.
     ln -s afile anotherfile
     ln -s ../adir/afile yetanotherfile

File: coreutils.info,  Node: mkdir invocation,  Next: mkfifo invocation,  Prev: ln invocation,  Up: Special file types

12.3 `mkdir': Make directories
==============================

`mkdir' creates directories with the specified names.  Synopsis:

     mkdir [OPTION]... NAME...

   `mkdir' creates each directory NAME in the order given.  It reports
an error if NAME already exists, unless the `-p' option is given and
NAME is a directory.

   The program accepts the following options.  Also see *note Common
options::.

`-m MODE'
`--mode=MODE'
     Set the file permission bits of created directories to MODE, which
     uses the same syntax as in `chmod' and uses `a=rwx' (read, write
     and execute allowed for everyone) for the point of the departure.
     *Note File permissions::.

     Normally the directory has the desired file mode bits at the
     moment it is created.  As a GNU extension, MODE may also mention
     special mode bits, but in this case there may be a temporary window
     during which the directory exists but its special mode bits are
     incorrect.  *Note Directory Setuid and Setgid::, for how the
     set-user-ID and set-group-ID bits of directories are inherited
     unless overridden in this way.

     Note: The `--mode',`-m' option only applies to the right-most
     directories listed on the command line.  When combined with
     `--parents', `-p' option, any parent directories are created with
     `u+wx' modified by umask.

`-p'
`--parents'
     Make any missing parent directories for each argument, setting
     their file permission bits to the umask modified by `u+wx'.  Ignore
     existing parent directories, and do not change their file
     permission bits.

     To set the file permission bits of any newly-created parent
     directories to a value that includes `u+wx', you can set the umask
     before invoking `mkdir'.  For example, if the shell command
     `(umask u=rwx,go=rx; mkdir -p P/Q)' creates the parent `P' it sets
     the parent's permission bits to `u=rwx,go=rx'.  To set a parent's
     special mode bits as well, you can invoke `chmod' after `mkdir'.
     *Note Directory Setuid and Setgid::, for how the set-user-ID and
     set-group-ID bits of newly-created parent directories are
     inherited.

     When COREUTILS_CHILD_DEFAULT_ACLS environment variable is set,
     `parents', `-p' respects default umask and ACLs, as it does in Red
     Hat Enterprise Linux 7.

`-v'
`--verbose'
     Print a message for each created directory.  This is most useful
     with `--parents'.

`-Z CONTEXT'
`--context=CONTEXT'
     Set the default SELinux security context to be used for created
     directories.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: mkfifo invocation,  Next: mknod invocation,  Prev: mkdir invocation,  Up: Special file types

12.4 `mkfifo': Make FIFOs (named pipes)
=======================================

`mkfifo' creates FIFOs (also called "named pipes") with the specified
names.  Synopsis:

     mkfifo [OPTION] NAME...

   A "FIFO" is a special file type that permits independent processes
to communicate.  One process opens the FIFO file for writing, and
another for reading, after which data can flow as with the usual
anonymous pipe in shells or elsewhere.

   The program accepts the following option.  Also see *note Common
options::.

`-m MODE'
`--mode=MODE'
     Set the mode of created FIFOs to MODE, which is symbolic as in
     `chmod' and uses `a=rw' (read and write allowed for everyone) for
     the point of departure.  MODE should specify only file permission
     bits.  When COREUTILS_CHILD_DEFAULT_ACLS environment variable is
     set, `mode',`-m' respects default umask and ACLs, as it does in
     Red Hat Enterprise Linux 7.  *Note File permissions::.

`-Z CONTEXT'
`--context=CONTEXT'
     Set the default SELinux security context to be used for created
     FIFOs.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: mknod invocation,  Next: readlink invocation,  Prev: mkfifo invocation,  Up: Special file types

12.5 `mknod': Make block or character special files
===================================================

`mknod' creates a FIFO, character special file, or block special file
with the specified name.  Synopsis:

     mknod [OPTION]... NAME TYPE [MAJOR MINOR]

   Unlike the phrase "special file type" above, the term "special file"
has a technical meaning on Unix: something that can generate or receive
data.  Usually this corresponds to a physical piece of hardware, e.g.,
a printer or a disk.  (These files are typically created at
system-configuration time.)  The `mknod' command is what creates files
of this type.  Such devices can be read either a character at a time or
a "block" (many characters) at a time, hence we say there are "block
special" files and "character special" files.

   Due to shell aliases and built-in `mknod' command, using an
unadorned `mknod' interactively or in a script may get you different
functionality than that described here.  Invoke it via `env' (i.e.,
`env mknod ...') to avoid interference from the shell.

   The arguments after NAME specify the type of file to make:

`p'
     for a FIFO

`b'
     for a block special file

`c'
     for a character special file


   When making a block or character special file, the major and minor
device numbers must be given after the file type.  If a major or minor
device number begins with `0x' or `0X', it is interpreted as
hexadecimal; otherwise, if it begins with `0', as octal; otherwise, as
decimal.

   The program accepts the following option.  Also see *note Common
options::.

`-m MODE'
`--mode=MODE'
     Set the mode of created files to MODE, which is symbolic as in
     `chmod' and uses `a=rw' as the point of departure.  MODE should
     specify only file permission bits.  When
     COREUTILS_CHILD_DEFAULT_ACLS environment variable is set,
     `mode',`-m' respects default umask and ACLs, as it does in Red Hat
     Enterprise Linux 7.  *Note File permissions::.

`-Z CONTEXT'
`--context=CONTEXT'
     Set the default SELinux security context to be used for created
     files.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: readlink invocation,  Next: rmdir invocation,  Prev: mknod invocation,  Up: Special file types

12.6 `readlink': Print value of a symlink or canonical file name
================================================================

`readlink' may work in one of two supported modes:

`Readlink mode'
     `readlink' outputs the value of the given symbolic link.  If
     `readlink' is invoked with an argument other than the name of a
     symbolic link, it produces no output and exits with a nonzero exit
     code.

`Canonicalize mode'
     `readlink' outputs the absolute name of the given file which
     contains no `.', `..' components nor any repeated separators (`/')
     or symbolic links.


     readlink [OPTION] FILE

   By default, `readlink' operates in readlink mode.

   The program accepts the following options.  Also see *note Common
options::.

`-f'
`--canonicalize'
     Activate canonicalize mode.  If any component of the file name
     except the last one is missing or unavailable, `readlink' produces
     no output and exits with a nonzero exit code.  A trailing slash is
     ignored.

`-e'
`--canonicalize-existing'
     Activate canonicalize mode.  If any component is missing or
     unavailable, `readlink' produces no output and exits with a
     nonzero exit code.  A trailing slash requires that the name
     resolve to a directory.

`-m'
`--canonicalize-missing'
     Activate canonicalize mode.  If any component is missing or
     unavailable, `readlink' treats it as a directory.

`-n'
`--no-newline'
     Do not output the trailing newline.

`-s'
`-q'
`--silent'
`--quiet'
     Suppress most error messages.

`-v'
`--verbose'
     Report error messages.


   The `readlink' utility first appeared in OpenBSD 2.1.

   There is a `realpath' command on some systems which operates like
`readlink' in canonicalize mode.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: rmdir invocation,  Next: unlink invocation,  Prev: readlink invocation,  Up: Special file types

12.7 `rmdir': Remove empty directories
======================================

`rmdir' removes empty directories.  Synopsis:

     rmdir [OPTION]... DIRECTORY...

   If any DIRECTORY argument does not refer to an existing empty
directory, it is an error.

   The program accepts the following options.  Also see *note Common
options::.

`--ignore-fail-on-non-empty'
     Ignore each failure to remove a directory that is solely because
     the directory is non-empty.

`-p'
`--parents'
     Remove DIRECTORY, then try to remove each component of DIRECTORY.
     So, for example, `rmdir -p a/b/c' is similar to `rmdir a/b/c a/b
     a'.  As such, it fails if any of those directories turns out not
     to be empty.  Use the `--ignore-fail-on-non-empty' option to make
     it so such a failure does not evoke a diagnostic and does not
     cause `rmdir' to exit unsuccessfully.

`-v'
`--verbose'
     Give a diagnostic for each successful removal.  DIRECTORY is
     removed.


   *Note rm invocation::, for how to remove non-empty directories
(recursively).

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: unlink invocation,  Prev: rmdir invocation,  Up: Special file types

12.8 `unlink': Remove files via the unlink syscall
==================================================

`unlink' deletes a single specified file name.  It is a minimalist
interface to the system-provided `unlink' function.  *Note Deleting
Files: (libc)Deleting Files.  Synopsis: It avoids the bells and
whistles of the more commonly-used `rm' command (*note rm invocation::).

     unlink FILENAME

   On some systems `unlink' can be used to delete the name of a
directory.  On others, it can be used that way only by a privileged
user.  In the GNU system `unlink' can never delete the name of a
directory.

   The `unlink' command honors the `--help' and `--version' options.
To remove a file whose name begins with `-', prefix the name with `./',
e.g., `unlink ./--help'.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: Changing file attributes,  Next: Disk usage,  Prev: Special file types,  Up: Top

13 Changing file attributes
***************************

A file is not merely its contents, a name, and a file type (*note
Special file types::).  A file also has an owner (a user ID), a group
(a group ID), permissions (what the owner can do with the file, what
people in the group can do, and what everyone else can do), various
timestamps, and other information.  Collectively, we call these a file's
"attributes".

   These commands change file attributes.

* Menu:

* chgrp invocation::            Change file groups.
* chmod invocation::            Change access permissions.
* chown invocation::            Change file owners and groups.
* touch invocation::            Change file timestamps.

File: coreutils.info,  Node: chgrp invocation,  Next: chmod invocation,  Up: Changing file attributes

13.2 `chgrp': Change group ownership
====================================

`chgrp' changes the group ownership of each given FILE to GROUP (which
can be either a group name or a numeric group ID) or to the group of an
existing reference file.  Synopsis:

     chgrp [OPTION]... {GROUP | --reference=REF_FILE} FILE...

   If GROUP is intended to represent a numeric group ID, then you may
specify it with a leading `+'.  *Note Disambiguating names and IDs::.

   The program accepts the following options.  Also see *note Common
options::.

`-c'
`--changes'
     Verbosely describe the action for each FILE whose group actually
     changes.

`-f'
`--silent'
`--quiet'
     Do not print error messages about files whose group cannot be
     changed.

`--dereference'
     Do not act on symbolic links themselves but rather on what they
     point to.  This is the default.

`-h'
`--no-dereference'
     Act on symbolic links themselves instead of what they point to.
     This mode relies on the `lchown' system call.  On systems that do
     not provide the `lchown' system call, `chgrp' fails when a file
     specified on the command line is a symbolic link.  By default, no
     diagnostic is issued for symbolic links encountered during a
     recursive traversal, but see `--verbose'.

`--preserve-root'
     Fail upon any attempt to recursively change the root directory,
     `/'.  Without `--recursive', this option has no effect.  *Note
     Treating / specially::.

`--no-preserve-root'
     Cancel the effect of any preceding `--preserve-root' option.
     *Note Treating / specially::.

`--reference=REF_FILE'
     Change the group of each FILE to be the same as that of REF_FILE.
     If REF_FILE is a symbolic link, do not use the group of the
     symbolic link, but rather that of the file it refers to.

`-v'
`--verbose'
     Output a diagnostic for every file processed.  If a symbolic link
     is encountered during a recursive traversal on a system without
     the `lchown' system call, and `--no-dereference' is in effect,
     then issue a diagnostic saying neither the symbolic link nor its
     referent is being changed.

`-R'
`--recursive'
     Recursively change the group ownership of directories and their
     contents.

`-H'
     If `--recursive' (`-R') is specified and a command line argument
     is a symbolic link to a directory, traverse it.  *Note Traversing
     symlinks::.

`-L'
     In a recursive traversal, traverse every symbolic link to a
     directory that is encountered.  *Note Traversing symlinks::.

`-P'
     Do not traverse any symbolic links.  This is the default if none
     of `-H', `-L', or `-P' is specified.  *Note Traversing symlinks::.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Examples:

     # Change the group of /u to "staff".
     chgrp staff /u

     # Change the group of /u and subfiles to "staff".
     chgrp -hR staff /u

File: coreutils.info,  Node: chmod invocation,  Next: chown invocation,  Prev: chgrp invocation,  Up: Changing file attributes

13.3 `chmod': Change access permissions
=======================================

`chmod' changes the access permissions of the named files.  Synopsis:

     chmod [OPTION]... {MODE | --reference=REF_FILE} FILE...

   `chmod' never changes the permissions of symbolic links, since the
`chmod' system call cannot change their permissions.  This is not a
problem since the permissions of symbolic links are never used.
However, for each symbolic link listed on the command line, `chmod'
changes the permissions of the pointed-to file.  In contrast, `chmod'
ignores symbolic links encountered during recursive directory
traversals.

   A successful use of `chmod' clears the set-group-ID bit of a regular
file if the file's group ID does not match the user's effective group
ID or one of the user's supplementary group IDs, unless the user has
appropriate privileges.  Additional restrictions may cause the
set-user-ID and set-group-ID bits of MODE or REF_FILE to be ignored.
This behavior depends on the policy and functionality of the underlying
`chmod' system call.  When in doubt, check the underlying system
behavior.

   If used, MODE specifies the new file mode bits.  For details, see
the section on *note File permissions::.  If you really want MODE to
have a leading `-', you should use `--' first, e.g., `chmod -- -w
file'.  Typically, though, `chmod a-w file' is preferable, and `chmod -w
file' (without the `--') complains if it behaves differently from what
`chmod a-w file' would do.

   The program accepts the following options.  Also see *note Common
options::.

`-c'
`--changes'
     Verbosely describe the action for each FILE whose permissions
     actually changes.

`-f'
`--silent'
`--quiet'
     Do not print error messages about files whose permissions cannot be
     changed.

`--preserve-root'
     Fail upon any attempt to recursively change the root directory,
     `/'.  Without `--recursive', this option has no effect.  *Note
     Treating / specially::.

`--no-preserve-root'
     Cancel the effect of any preceding `--preserve-root' option.
     *Note Treating / specially::.

`-v'
`--verbose'
     Verbosely describe the action or non-action taken for every FILE.

`--reference=REF_FILE'
     Change the mode of each FILE to be the same as that of REF_FILE.
     *Note File permissions::.  If REF_FILE is a symbolic link, do not
     use the mode of the symbolic link, but rather that of the file it
     refers to.

`-R'
`--recursive'
     Recursively change permissions of directories and their contents.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: chown invocation,  Next: touch invocation,  Prev: chmod invocation,  Up: Changing file attributes

13.1 `chown': Change file owner and group
=========================================

`chown' changes the user and/or group ownership of each given FILE to
NEW-OWNER or to the user and group of an existing reference file.
Synopsis:

     chown [OPTION]... {NEW-OWNER | --reference=REF_FILE} FILE...

   If used, NEW-OWNER specifies the new owner and/or group as follows
(with no embedded white space):

     [OWNER] [ : [GROUP] ]

   Specifically:

OWNER
     If only an OWNER (a user name or numeric user ID) is given, that
     user is made the owner of each given file, and the files' group is
     not changed.

OWNER`:'GROUP
     If the OWNER is followed by a colon and a GROUP (a group name or
     numeric group ID), with no spaces between them, the group
     ownership of the files is changed as well (to GROUP).

OWNER`:'
     If a colon but no group name follows OWNER, that user is made the
     owner of the files and the group of the files is changed to
     OWNER's login group.

`:'GROUP
     If the colon and following GROUP are given, but the owner is
     omitted, only the group of the files is changed; in this case,
     `chown' performs the same function as `chgrp'.

`:'
     If only a colon is given, or if NEW-OWNER is empty, neither the
     owner nor the group is changed.


   If OWNER or GROUP is intended to represent a numeric user or group
ID, then you may specify it with a leading `+'.  *Note Disambiguating
names and IDs::.

   Some older scripts may still use `.' in place of the `:' separator.
POSIX 1003.1-2001 (*note Standards conformance::) does not require
support for that, but for backward compatibility GNU `chown' supports
`.' so long as no ambiguity results.  New scripts should avoid the use
of `.' because it is not portable, and because it has undesirable
results if the entire OWNER`.'GROUP happens to identify a user whose
name contains `.'.

   The `chown' command sometimes clears the set-user-ID or set-group-ID
permission bits.  This behavior depends on the policy and functionality
of the underlying `chown' system call, which may make system-dependent
file mode modifications outside the control of the `chown' command.
For example, the `chown' command might not affect those bits when
invoked by a user with appropriate privileges, or when the bits signify
some function other than executable permission (e.g., mandatory
locking).  When in doubt, check the underlying system behavior.

   The program accepts the following options.  Also see *note Common
options::.

`-c'
`--changes'
     Verbosely describe the action for each FILE whose ownership
     actually changes.

`-f'
`--silent'
`--quiet'
     Do not print error messages about files whose ownership cannot be
     changed.

`--from=OLD-OWNER'
     Change a FILE's ownership only if it has current attributes
     specified by OLD-OWNER.  OLD-OWNER has the same form as NEW-OWNER
     described above.  This option is useful primarily from a security
     standpoint in that it narrows considerably the window of potential
     abuse.  For example, to reflect a user ID numbering change for one
     user's files without an option like this, `root' might run

          find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER

     But that is dangerous because the interval between when the `find'
     tests the existing file's owner and when the `chown' is actually
     run may be quite large.  One way to narrow the gap would be to
     invoke chown for each file as it is found:

          find / -owner OLDUSER -exec chown -h NEWUSER {} \;

     But that is very slow if there are many affected files.  With this
     option, it is safer (the gap is narrower still) though still not
     perfect:

          chown -h -R --from=OLDUSER NEWUSER /

`--dereference'
     Do not act on symbolic links themselves but rather on what they
     point to.  This is the default.

`-h'
`--no-dereference'
     Act on symbolic links themselves instead of what they point to.
     This mode relies on the `lchown' system call.  On systems that do
     not provide the `lchown' system call, `chown' fails when a file
     specified on the command line is a symbolic link.  By default, no
     diagnostic is issued for symbolic links encountered during a
     recursive traversal, but see `--verbose'.

`--preserve-root'
     Fail upon any attempt to recursively change the root directory,
     `/'.  Without `--recursive', this option has no effect.  *Note
     Treating / specially::.

`--no-preserve-root'
     Cancel the effect of any preceding `--preserve-root' option.
     *Note Treating / specially::.

`--reference=REF_FILE'
     Change the user and group of each FILE to be the same as those of
     REF_FILE.  If REF_FILE is a symbolic link, do not use the user and
     group of the symbolic link, but rather those of the file it refers
     to.

`-v'
`--verbose'
     Output a diagnostic for every file processed.  If a symbolic link
     is encountered during a recursive traversal on a system without
     the `lchown' system call, and `--no-dereference' is in effect,
     then issue a diagnostic saying neither the symbolic link nor its
     referent is being changed.

`-R'
`--recursive'
     Recursively change ownership of directories and their contents.

`-H'
     If `--recursive' (`-R') is specified and a command line argument
     is a symbolic link to a directory, traverse it.  *Note Traversing
     symlinks::.

`-L'
     In a recursive traversal, traverse every symbolic link to a
     directory that is encountered.  *Note Traversing symlinks::.

`-P'
     Do not traverse any symbolic links.  This is the default if none
     of `-H', `-L', or `-P' is specified.  *Note Traversing symlinks::.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Examples:

     # Change the owner of /u to "root".
     chown root /u

     # Likewise, but also change its group to "staff".
     chown root:staff /u

     # Change the owner of /u and subfiles to "root".
     chown -hR root /u

File: coreutils.info,  Node: touch invocation,  Prev: chown invocation,  Up: Changing file attributes

13.4 `touch': Change file timestamps
====================================

`touch' changes the access and/or modification times of the specified
files.  Synopsis:

     touch [OPTION]... FILE...

   Any FILE argument that does not exist is created empty, unless
option `--no-create' (`-c') or `--no-dereference' (`-h') was in effect.

   A FILE argument string of `-' is handled specially and causes
`touch' to change the times of the file associated with standard output.

   If changing both the access and modification times to the current
time, `touch' can change the timestamps for files that the user running
it does not own but has write permission for.  Otherwise, the user must
own the files.

   Although `touch' provides options for changing two of the times--the
times of last access and modification--of a file, there is actually a
standard third one as well: the inode change time.  This is often
referred to as a file's `ctime'.  The inode change time represents the
time when the file's meta-information last changed.  One common example
of this is when the permissions of a file change.  Changing the
permissions doesn't access the file, so the atime doesn't change, nor
does it modify the file, so the mtime doesn't change.  Yet, something
about the file itself has changed, and this must be noted somewhere.
This is the job of the ctime field.  This is necessary, so that, for
example, a backup program can make a fresh copy of the file, including
the new permissions value.  Another operation that modifies a file's
ctime without affecting the others is renaming.  In any case, it is not
possible, in normal operations, for a user to change the ctime field to
a user-specified value.  Some operating systems and file systems
support a fourth time: the birth time, when the file was first created;
by definition, this timestamp never changes.

   Time stamps assume the time zone rules specified by the `TZ'
environment variable, or by the system default rules if `TZ' is not
set.  *Note Specifying the Time Zone with `TZ': (libc)TZ Variable.  You
can avoid ambiguities during daylight saving transitions by using UTC
time stamps.

   The program accepts the following options.  Also see *note Common
options::.

`-a'
`--time=atime'
`--time=access'
`--time=use'
     Change the access time only.

`-c'
`--no-create'
     Do not warn about or create files that do not exist.

`-d'
`--date=TIME'
     Use TIME instead of the current time.  It can contain month names,
     time zones, `am' and `pm', `yesterday', etc.  For example,
     `--date="2004-02-27 14:19:13.489392193 +0530"' specifies the
     instant of time that is 489,392,193 nanoseconds after February 27,
     2004 at 2:19:13 PM in a time zone that is 5 hours and 30 minutes
     east of UTC.  *Note Date input formats::.  File systems that do
     not support high-resolution time stamps silently ignore any excess
     precision here.

`-f'
     Ignored; for compatibility with BSD versions of `touch'.

`-h'
`--no-dereference'
     Attempt to change the timestamps of a symbolic link, rather than
     what the link refers to.  When using this option, empty files are
     not created, but option `-c' must also be used to avoid warning
     about files that do not exist.  Not all systems support changing
     the timestamps of symlinks, since underlying system support for
     this action was not required until POSIX 2008.  Also, on some
     systems, the mere act of examining a symbolic link changes the
     access time, such that only changes to the modification time will
     persist long enough to be observable.  When coupled with option
     `-r', a reference timestamp is taken from a symbolic link rather
     than the file it refers to.

`-m'
`--time=mtime'
`--time=modify'
     Change the modification time only.

`-r FILE'
`--reference=FILE'
     Use the times of the reference FILE instead of the current time.
     If this option is combined with the `--date=TIME' (`-d TIME')
     option, the reference FILE's time is the origin for any relative
     TIMEs given, but is otherwise ignored.  For example, `-r foo -d
     '-5 seconds'' specifies a time stamp equal to five seconds before
     the corresponding time stamp for `foo'.  If FILE is a symbolic
     link, the reference timestamp is taken from the target of the
     symlink, unless `-h' was also in effect.

`-t [[CC]YY]MMDDHHMM[.SS]'
     Use the argument (optional four-digit or two-digit years, months,
     days, hours, minutes, optional seconds) instead of the current
     time.  If the year is specified with only two digits, then CC is
     20 for years in the range 0 ... 68, and 19 for years in 69 ... 99.
     If no digits of the year are specified, the argument is
     interpreted as a date in the current year.  Note that SS may be
     `60', to accommodate leap seconds.


   On older systems, `touch' supports an obsolete syntax, as follows.
If no timestamp is given with any of the `-d', `-r', or `-t' options,
and if there are two or more FILEs and the first FILE is of the form
`MMDDHHMM[YY]' and this would be a valid argument to the `-t' option
(if the YY, if any, were moved to the front), and if the represented
year is in the range 1969-1999, that argument is interpreted as the time
for the other files instead of as a file name.  This obsolete behavior
can be enabled or disabled with the `_POSIX2_VERSION' environment
variable (*note Standards conformance::), but portable scripts should
avoid commands whose behavior depends on this variable.  For example,
use `touch ./12312359 main.c' or `touch -t 12312359 main.c' rather than
the ambiguous `touch 12312359 main.c'.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: Disk usage,  Next: Printing text,  Prev: Changing file attributes,  Up: Top

14 Disk usage
*************

No disk can hold an infinite amount of data.  These commands report how
much disk storage is in use or available, report other file and file
status information, and write buffers to disk.

* Menu:

* df invocation::               Report file system disk space usage.
* du invocation::               Estimate file space usage.
* stat invocation::             Report file or file system status.
* sync invocation::             Synchronize memory and disk.
* truncate invocation::         Shrink or extend the size of a file.

File: coreutils.info,  Node: df invocation,  Next: du invocation,  Up: Disk usage

14.1 `df': Report file system disk space usage
==============================================

`df' reports the amount of disk space used and available on file
systems.  Synopsis:

     df [OPTION]... [FILE]...

   With no arguments, `df' reports the space used and available on all
currently mounted file systems (of all types).  Otherwise, `df' reports
on the file system containing each argument FILE.

   Normally the disk space is printed in units of 1024 bytes, but this
can be overridden (*note Block size::).  Non-integer quantities are
rounded up to the next higher unit.

   If an argument FILE is a disk device file containing a mounted file
system, `df' shows the space available on that file system rather than
on the file system containing the device node (i.e., the root file
system).  GNU `df' does not attempt to determine the disk usage on
unmounted file systems, because on most kinds of systems doing so
requires extremely nonportable intimate knowledge of file system
structures.

   The program accepts the following options.  Also see *note Common
options::.

`-a'
`--all'
     Include in the listing dummy file systems, which are omitted by
     default.  Such file systems are typically special-purpose
     pseudo-file-systems, such as automounter entries.

`-B SIZE'
`--block-size=SIZE'
     Scale sizes by SIZE before printing them (*note Block size::).
     For example, `-BG' prints sizes in units of 1,073,741,824 bytes.

`--direct'
     Do not resolve mount point and show statistics directly for a
     file. It can be especially useful for NFS mount points if there is
     a boundary between two storage policies behind the mount point.

`--total'
     Print a grand total of all arguments after all arguments have been
     processed.  This can be used to find out the total disk size, usage
     and available space of all listed devices.

`-h'
`--human-readable'
     Append a size letter to each size, such as `M' for mebibytes.
     Powers of 1024 are used, not 1000; `M' stands for 1,048,576 bytes.
     This option is equivalent to `--block-size=human-readable'.  Use
     the `--si' option if you prefer powers of 1000.

`-H'
     Equivalent to `--si'.

`-i'
`--inodes'
     List inode usage information instead of block usage.  An inode
     (short for index node) contains information about a file such as
     its owner, permissions, timestamps, and location on the disk.

`-k'
     Print sizes in 1024-byte blocks, overriding the default block size
     (*note Block size::).  This option is equivalent to
     `--block-size=1K'.

`-l'
`--local'
     Limit the listing to local file systems.  By default, remote file
     systems are also listed.

`--no-sync'
     Do not invoke the `sync' system call before getting any usage data.
     This may make `df' run significantly faster on systems with many
     disks, but on some systems (notably SunOS) the results may be
     slightly out of date.  This is the default.

`-P'
`--portability'
     Use the POSIX output format.  This is like the default format
     except for the following:

       1. The information about each file system is always printed on
          exactly one line; a mount device is never put on a line by
          itself.  This means that if the mount device name is more
          than 20 characters long (e.g., for some network mounts), the
          columns are misaligned.

       2. The labels in the header output line are changed to conform
          to POSIX.

       3. The default block size and output format are unaffected by the
          `DF_BLOCK_SIZE', `BLOCK_SIZE' and `BLOCKSIZE' environment
          variables.  However, the default block size is still affected
          by `POSIXLY_CORRECT': it is 512 if `POSIXLY_CORRECT' is set,
          1024 otherwise.  *Note Block size::.

`--si'
     Append an SI-style abbreviation to each size, such as `M' for
     megabytes.  Powers of 1000 are used, not 1024; `M' stands for
     1,000,000 bytes.  This option is equivalent to `--block-size=si'.
     Use the `-h' or `--human-readable' option if you prefer powers of
     1024.

`--sync'
     Invoke the `sync' system call before getting any usage data.  On
     some systems (notably SunOS), doing this yields more up to date
     results, but in general this option makes `df' much slower,
     especially when there are many or very busy file systems.

`-t FSTYPE'
`--type=FSTYPE'
     Limit the listing to file systems of type FSTYPE.  Multiple file
     system types can be specified by giving multiple `-t' options.  By
     default, nothing is omitted.

`-T'
`--print-type'
     Print each file system's type.  The types printed here are the
     same ones you can include or exclude with `-t' and `-x'.  The
     particular types printed are whatever is supported by the system.
     Here are some of the common names (this list is certainly not
     exhaustive):

    `nfs'
          An NFS file system, i.e., one mounted over a network from
          another machine.  This is the one type name which seems to be
          used uniformly by all systems.

    `4.2, ufs, efs...'
          A file system on a locally-mounted hard disk.  (The system
          might even support more than one type here; Linux does.)

    `hsfs, cdfs'
          A file system on a CD-ROM drive.  HP-UX uses `cdfs', most
          other systems use `hsfs' (`hs' for "High Sierra").

    `pcfs'
          An MS-DOS file system, usually on a diskette.


`-x FSTYPE'
`--exclude-type=FSTYPE'
     Limit the listing to file systems not of type FSTYPE.  Multiple
     file system types can be eliminated by giving multiple `-x'
     options.  By default, no file system types are omitted.

`-v'
     Ignored; for compatibility with System V versions of `df'.


   An exit status of zero indicates success, and a nonzero value
indicates failure.  Failure includes the case where no output is
generated, so you can inspect the exit status of a command like `df -t
ext3 -t reiserfs DIR' to test whether DIR is on a file system of type
`ext3' or `reiserfs'.

File: coreutils.info,  Node: du invocation,  Next: stat invocation,  Prev: df invocation,  Up: Disk usage

14.2 `du': Estimate file space usage
====================================

`du' reports the amount of disk space used by the specified files and
for each subdirectory (of directory arguments).  Synopsis:

     du [OPTION]... [FILE]...

   With no arguments, `du' reports the disk space for the current
directory.  Normally the disk space is printed in units of 1024 bytes,
but this can be overridden (*note Block size::).  Non-integer
quantities are rounded up to the next higher unit.

   If two or more hard links point to the same file, only one of the
hard links is counted.  The FILE argument order affects which links are
counted, and changing the argument order may change the numbers that
`du' outputs.

   The program accepts the following options.  Also see *note Common
options::.

`-a'
`--all'
     Show counts for all files, not just directories.

`--apparent-size'
     Print apparent sizes, rather than disk usage.  The apparent size
     of a file is the number of bytes reported by `wc -c' on regular
     files, or more generally, `ls -l --block-size=1' or `stat
     --format=%s'.  For example, a file containing the word `zoo' with
     no newline would, of course, have an apparent size of 3.  Such a
     small file may require anywhere from 0 to 16 KiB or more of disk
     space, depending on the type and configuration of the file system
     on which the file resides.  However, a sparse file created with
     this command:

          dd bs=1 seek=2GiB if=/dev/null of=big

     has an apparent size of 2 GiB, yet on most modern systems, it
     actually uses almost no disk space.

`-b'
`--bytes'
     Equivalent to `--apparent-size --block-size=1'.

`-B SIZE'
`--block-size=SIZE'
     Scale sizes by SIZE before printing them (*note Block size::).
     For example, `-BG' prints sizes in units of 1,073,741,824 bytes.

`-c'
`--total'
     Print a grand total of all arguments after all arguments have been
     processed.  This can be used to find out the total disk usage of a
     given set of files or directories.

`-D'
`--dereference-args'
     Dereference symbolic links that are command line arguments.  Does
     not affect other symbolic links.  This is helpful for finding out
     the disk usage of directories, such as `/usr/tmp', which are often
     symbolic links.

`--files0-from=FILE'
     Disallow processing files named on the command line, and instead
     process those named in file FILE; each name being terminated by a
     zero byte (ASCII NUL).  This is useful when the list of file names
     is so long that it may exceed a command line length limitation.
     In such cases, running `du' via `xargs' is undesirable because it
     splits the list into pieces and makes `du' print with the
     `--total' (`-c') option for each sublist rather than for the
     entire list.  One way to produce a list of ASCII NUL terminated
     file names is with GNU `find', using its `-print0' predicate.  If
     FILE is `-' then the ASCII NUL terminated file names are read from
     standard input.

`-h'
`--human-readable'
     Append a size letter to each size, such as `M' for mebibytes.
     Powers of 1024 are used, not 1000; `M' stands for 1,048,576 bytes.
     This option is equivalent to `--block-size=human-readable'.  Use
     the `--si' option if you prefer powers of 1000.

`-H'
     Equivalent to `--dereference-args' (`-D').

`-k'
     Print sizes in 1024-byte blocks, overriding the default block size
     (*note Block size::).  This option is equivalent to
     `--block-size=1K'.

`-l'
`--count-links'
     Count the size of all files, even if they have appeared already
     (as a hard link).

`-L'
`--dereference'
     Dereference symbolic links (show the disk space used by the file
     or directory that the link points to instead of the space used by
     the link).

`-m'
     Print sizes in 1,048,576-byte blocks, overriding the default block
     size (*note Block size::).  This option is equivalent to
     `--block-size=1M'.

`-P'
`--no-dereference'
     For each symbolic links encountered by `du', consider the disk
     space used by the symbolic link.

`--max-depth=DEPTH'
     Show the total for each directory (and file if -all) that is at
     most MAX_DEPTH levels down from the root of the hierarchy.  The
     root is at level 0, so `du --max-depth=0' is equivalent to `du -s'.

`-0'
`--null'
     Output a zero byte (ASCII NUL) at the end of each line, rather
     than a newline. This option enables other programs to parse the
     output of `du' even when that output would contain data with
     embedded newlines.

`--si'
     Append an SI-style abbreviation to each size, such as `M' for
     megabytes.  Powers of 1000 are used, not 1024; `M' stands for
     1,000,000 bytes.  This option is equivalent to `--block-size=si'.
     Use the `-h' or `--human-readable' option if you prefer powers of
     1024.

`-s'
`--summarize'
     Display only a total for each argument.

`-S'
`--separate-dirs'
     Normally, in the output of `du' (when not using `--summarize'),
     the size listed next to a directory name, D, represents the sum of
     sizes of all entries beneath D as well as the size of D itself.
     With `--separate-dirs', the size reported for a directory name, D,
     is merely the `stat.st_size'-derived size of the directory entry,
     D.

`--time'
     Show time of the most recent modification of any file in the
     directory, or any of its subdirectories.

`--time=ctime'
`--time=status'
`--time=use'
     Show the most recent status change time (the `ctime' in the inode)
     of any file in the directory, instead of the modification time.

`--time=atime'
`--time=access'
     Show the most recent access time (the `atime' in the inode) of any
     file in the directory, instead of the modification time.

`--time-style=STYLE'
     List timestamps in style STYLE.  This option has an effect only if
     the `--time' option is also specified.  The STYLE should be one of
     the following:

    `+FORMAT'
          List timestamps using FORMAT, where FORMAT is interpreted
          like the format argument of `date' (*note date invocation::).
          For example, `--time-style="+%Y-%m-%d %H:%M:%S"' causes `du'
          to list timestamps like `2002-03-30 23:45:56'.  As with
          `date', FORMAT's interpretation is affected by the `LC_TIME'
          locale category.

    `full-iso'
          List timestamps in full using ISO 8601 date, time, and time
          zone format with nanosecond precision, e.g., `2002-03-30
          23:45:56.477817180 -0700'.  This style is equivalent to
          `+%Y-%m-%d %H:%M:%S.%N %z'.

    `long-iso'
          List ISO 8601 date and time in minutes, e.g., `2002-03-30
          23:45'.  These timestamps are shorter than `full-iso'
          timestamps, and are usually good enough for everyday work.
          This style is equivalent to `+%Y-%m-%d %H:%M'.

    `iso'
          List ISO 8601 dates for timestamps, e.g., `2002-03-30'.  This
          style is equivalent to `+%Y-%m-%d'.

     You can specify the default value of the `--time-style' option
     with the environment variable `TIME_STYLE'; if `TIME_STYLE' is not
     set the default style is `long-iso'.  For compatibility with `ls',
     if `TIME_STYLE' begins with `+' and contains a newline, the
     newline and any later characters are ignored; if `TIME_STYLE'
     begins with `posix-' the `posix-' is ignored; and if `TIME_STYLE'
     is `locale' it is ignored.

`-x'
`--one-file-system'
     Skip directories that are on different file systems from the one
     that the argument being processed is on.

`--exclude=PATTERN'
     When recursing, skip subdirectories or files matching PATTERN.
     For example, `du --exclude='*.o'' excludes files whose names end
     in `.o'.

`-X FILE'
`--exclude-from=FILE'
     Like `--exclude', except take the patterns to exclude from FILE,
     one per line.  If FILE is `-', take the patterns from standard
     input.


   On BSD systems, `du' reports sizes that are half the correct values
for files that are NFS-mounted from HP-UX systems.  On HP-UX systems,
it reports sizes that are twice the correct values for files that are
NFS-mounted from BSD systems.  This is due to a flaw in HP-UX; it also
affects the HP-UX `du' program.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: stat invocation,  Next: sync invocation,  Prev: du invocation,  Up: Disk usage

14.3 `stat': Report file or file system status
==============================================

`stat' displays information about the specified file(s).  Synopsis:

     stat [OPTION]... [FILE]...

   With no option, `stat' reports all information about the given files.
But it also can be used to report the information of the file systems
the given files are located on.  If the files are links, `stat' can
also give information about the files the links point to.

   Due to shell aliases and built-in `stat' command, using an unadorned
`stat' interactively or in a script may get you different functionality
than that described here.  Invoke it via `env' (i.e., `env stat ...')
to avoid interference from the shell.

`-L'
`--dereference'
     Change how `stat' treats symbolic links.  With this option, `stat'
     acts on the file referenced by each symbolic link argument.
     Without it, `stat' acts on any symbolic link argument directly.

`-f'
`--file-system'
     Report information about the file systems where the given files
     are located instead of information about the files themselves.

`-c'
`--format=FORMAT'
     Use FORMAT rather than the default format.  FORMAT is
     automatically newline-terminated, so running a command like the
     following with two or more FILE operands produces a line of output
     for each operand:
          $ stat --format=%d:%i / /usr
          2050:2
          2057:2

`--printf=FORMAT'
     Use FORMAT rather than the default format.  Like `--format', but
     interpret backslash escapes, and do not output a mandatory
     trailing newline.  If you want a newline, include `\n' in the
     FORMAT.  Here's how you would use `--printf' to print the device
     and inode numbers of `/' and `/usr':
          $ stat --printf='%d:%i\n' / /usr
          2050:2
          2057:2

`-t'
`--terse'
     Print the information in terse form, suitable for parsing by other
     programs.


   The valid FORMAT directives for files with `--format' and `--printf'
are:

   * %a - Access rights in octal

   * %A - Access rights in human readable form

   * %b - Number of blocks allocated (see `%B')

   * %B - The size in bytes of each block reported by `%b'

   * %d - Device number in decimal

   * %D - Device number in hex

   * %f - Raw mode in hex

   * %F - File type

   * %g - Group ID of owner

   * %G - Group name of owner

   * %h - Number of hard links

   * %i - Inode number

   * %n - File name

   * %N - Quoted file name with dereference if symbolic link

   * %o - I/O block size

   * %s - Total size, in bytes

   * %t - Major device type in hex

   * %T - Minor device type in hex

   * %u - User ID of owner

   * %U - User name of owner

   * %x - Time of last access

   * %X - Time of last access as seconds since Epoch

   * %y - Time of last modification

   * %Y - Time of last modification as seconds since Epoch

   * %z - Time of last change

   * %Z - Time of last change as seconds since Epoch

   When listing file system information (`--file-system' (`-f')), you
must use a different set of FORMAT directives:

   * %a - Free blocks available to non-super-user

   * %b - Total data blocks in file system

   * %c - Total file nodes in file system

   * %d - Free file nodes in file system

   * %f - Free blocks in file system

   * %i - File System ID in hex

   * %l - Maximum length of file names

   * %n - File name

   * %s - Block size (for faster transfers)

   * %S - Fundamental block size (for block counts)

   * %t - Type in hex

   * %T - Type in human readable form

   Time stamps are listed according to the time zone rules specified by
the `TZ' environment variable, or by the system default rules if `TZ'
is not set.  *Note Specifying the Time Zone with `TZ': (libc)TZ
Variable.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: sync invocation,  Next: truncate invocation,  Prev: stat invocation,  Up: Disk usage

14.4 `sync': Synchronize data on disk with memory
=================================================

`sync' writes any data buffered in memory out to disk.  This can
include (but is not limited to) modified superblocks, modified inodes,
and delayed reads and writes.  This must be implemented by the kernel;
The `sync' program does nothing but exercise the `sync' system call.

   The kernel keeps data in memory to avoid doing (relatively slow) disk
reads and writes.  This improves performance, but if the computer
crashes, data may be lost or the file system corrupted as a result.
The `sync' command ensures everything in memory is written to disk.

   Any arguments are ignored, except for a lone `--help' or `--version'
(*note Common options::).

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: truncate invocation,  Prev: sync invocation,  Up: Disk usage

14.5 `truncate': Shrink or extend the size of a file
====================================================

`truncate' shrinks or extends the size of each FILE to the specified
size. Synopsis:

     truncate OPTION... FILE...

   Any FILE that does not exist is created.

   If a FILE is larger than the specified size, the extra data is lost.
If a FILE is shorter, it is extended and the extended part (or hole)
reads as zero bytes.

   The program accepts the following options.  Also see *note Common
options::.

`-c'
`--no-create'
     Do not create files that do not exist.

`-o'
`--io-blocks'
     Treat SIZE as number of I/O blocks of the FILE rather than bytes.

`-r RFILE'
`--reference=RFILE'
     Set the size of each FILE to the same size as RFILE.

`-s SIZE'
`--size=SIZE'
     Set the size of each FILE to this SIZE.  SIZE may be, or may be an
     integer optionally followed by, one of the following
     multiplicative suffixes:
          `KB' =>           1000 (KiloBytes)
          `K'  =>           1024 (KibiBytes)
          `MB' =>      1000*1000 (MegaBytes)
          `M'  =>      1024*1024 (MebiBytes)
          `GB' => 1000*1000*1000 (GigaBytes)
          `G'  => 1024*1024*1024 (GibiBytes)
     and so on for `T', `P', `E', `Z', and `Y'.

     SIZE may also be prefixed by one of the following to adjust the
     size of each FILE based on their current size:
          `+'  => extend by
          `-'  => reduce by
          `<'  => at most
          `>'  => at least
          `/'  => round down to multiple of
          `%'  => round up to multiple of


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: Printing text,  Next: Conditions,  Prev: Disk usage,  Up: Top

15 Printing text
****************

This section describes commands that display text strings.

* Menu:

* echo invocation::             Print a line of text.
* printf invocation::           Format and print data.
* yes invocation::              Print a string until interrupted.

File: coreutils.info,  Node: echo invocation,  Next: printf invocation,  Up: Printing text

15.1 `echo': Print a line of text
=================================

`echo' writes each given STRING to standard output, with a space
between each and a newline after the last one.  Synopsis:

     echo [OPTION]... [STRING]...

   Due to shell aliases and built-in `echo' command, using an unadorned
`echo' interactively or in a script may get you different functionality
than that described here.  Invoke it via `env' (i.e., `env echo ...')
to avoid interference from the shell.

   The program accepts the following options.  Also see *note Common
options::.  Options must precede operands, and the normally-special
argument `--' has no special meaning and is treated like any other
STRING.

`-n'
     Do not output the trailing newline.

`-e'
     Enable interpretation of the following backslash-escaped
     characters in each STRING:

    `\a'
          alert (bell)

    `\b'
          backspace

    `\c'
          produce no further output

    `\e'
          escape

    `\f'
          form feed

    `\n'
          newline

    `\r'
          carriage return

    `\t'
          horizontal tab

    `\v'
          vertical tab

    `\\'
          backslash

    `\0NNN'
          the eight-bit value that is the octal number NNN (zero to
          three octal digits), if NNN is a nine-bit value, the ninth
          bit is ignored

    `\NNN'
          the eight-bit value that is the octal number NNN (one to
          three octal digits), if NNN is a nine-bit value, the ninth
          bit is ignored

    `\xHH'
          the eight-bit value that is the hexadecimal number HH (one or
          two hexadecimal digits)

`-E'
     Disable interpretation of backslash escapes in each STRING.  This
     is the default.  If `-e' and `-E' are both specified, the last one
     given takes effect.


   If the `POSIXLY_CORRECT' environment variable is set, then when
`echo''s first argument is not `-n' it outputs option-like arguments
instead of treating them as options.  For example, `echo -ne hello'
outputs `-ne hello' instead of plain `hello'.

   POSIX does not require support for any options, and says that the
behavior of `echo' is implementation-defined if any STRING contains a
backslash or if the first argument is `-n'.  Portable programs can use
the `printf' command if they need to omit trailing newlines or output
control characters or backslashes.  *Note printf invocation::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: printf invocation,  Next: yes invocation,  Prev: echo invocation,  Up: Printing text

15.2 `printf': Format and print data
====================================

`printf' does formatted printing of text.  Synopsis:

     printf FORMAT [ARGUMENT]...

   `printf' prints the FORMAT string, interpreting `%' directives and
`\' escapes to format numeric and string arguments in a way that is
mostly similar to the C `printf' function.  *Note `printf' format
directives: (libc)Output Conversion Syntax, for details.  The
differences are listed below.

   Due to shell aliases and built-in `printf' command, using an
unadorned `printf' interactively or in a script may get you different
functionality than that described here.  Invoke it via `env' (i.e.,
`env printf ...') to avoid interference from the shell.

   * The FORMAT argument is reused as necessary to convert all the
     given ARGUMENTs.  For example, the command `printf %s a b' outputs
     `ab'.

   * Missing ARGUMENTs are treated as null strings or as zeros,
     depending on whether the context expects a string or a number.  For
     example, the command `printf %sx%d' prints `x0'.

   * An additional escape, `\c', causes `printf' to produce no further
     output.  For example, the command `printf 'A%sC\cD%sF' B E' prints
     `ABC'.

   * The hexadecimal escape sequence `\xHH' has at most two digits, as
     opposed to C where it can have an unlimited number of digits.  For
     example, the command `printf '\x07e'' prints two bytes, whereas
     the C statement `printf ("\x07e")' prints just one.

   * `printf' has an additional directive, `%b', which prints its
     argument string with `\' escapes interpreted in the same way as in
     the FORMAT string, except that octal escapes are of the form
     `\0OOO' where OOO is 0 to 3 octal digits. If `\OOO' is a nine-bit
     value, ignore the ninth bit.

     If a precision is also given, it limits the number of bytes printed
     from the converted string.

   * Numeric arguments must be single C constants, possibly with leading
     `+' or `-'.  For example, `printf %.4d -3' outputs `-0003'.

   * If the leading character of a numeric argument is `"' or `'' then
     its value is the numeric value of the immediately following
     character.  Any remaining characters are silently ignored if the
     `POSIXLY_CORRECT' environment variable is set; otherwise, a
     warning is printed.  For example, `printf "%d" "'a"' outputs `97'
     on hosts that use the ASCII character set, since `a' has the
     numeric value 97 in ASCII.


   A floating-point argument must use a period before any fractional
digits, but is printed according to the `LC_NUMERIC' category of the
current locale.  For example, in a locale whose radix character is a
comma, the command `printf %g 3.14' outputs `3,14' whereas the command
`printf %g 3,14' is an error.

   `printf' interprets `\OOO' in FORMAT as an octal number (if OOO is 1
to 3 octal digits) specifying a byte to print, and `\xHH' as a
hexadecimal number (if HH is 1 to 2 hex digits) specifying a character
to print.  Note however that when `\OOO' specifies a number larger than
255, the ninth bit is ignored.  For example, `printf '\400'' is
equivalent to `printf '\0''.

   `printf' interprets two character syntaxes introduced in ISO C 99:
`\u' for 16-bit Unicode (ISO/IEC 10646) characters, specified as four
hexadecimal digits HHHH, and `\U' for 32-bit Unicode characters,
specified as eight hexadecimal digits HHHHHHHH.  `printf' outputs the
Unicode characters according to the `LC_CTYPE' locale.  Unicode
characters in the ranges U+0000...U+009F, U+D800...U+DFFF cannot be
specified by this syntax, except for U+0024 ($), U+0040 (@), and U+0060
()`.

   The processing of `\u' and `\U' requires a full-featured `iconv'
facility.  It is activated on systems with glibc 2.2 (or newer), or
when `libiconv' is installed prior to this package.  Otherwise `\u' and
`\U' will print as-is.

   The only options are a lone `--help' or `--version'.  *Note Common
options::.  Options must precede operands.

   The Unicode character syntaxes are useful for writing strings in a
locale independent way.  For example, a string containing the Euro
currency symbol

     $ env printf '\u20AC 14.95'

will be output correctly in all locales supporting the Euro symbol
(ISO-8859-15, UTF-8, and others).  Similarly, a Chinese string

     $ env printf '\u4e2d\u6587'

will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8,
etc).

   Note that in these examples, the `printf' command has been invoked
via `env' to ensure that we run the program found via your shell's
search path, and not a shell alias or a built-in function.

   For larger strings, you don't need to look up the hexadecimal code
values of each character one by one.  ASCII characters mixed with \u
escape sequences is also known as the JAVA source file encoding.  You
can use GNU recode 3.5c (or newer) to convert strings to this encoding.
Here is how to convert a piece of text into a shell script which will
output this text in a locale-independent way:

     $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
         '\u4e2d\u6587\n' > sample.txt
     $ recode BIG5..JAVA < sample.txt \
         | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
         > sample.sh

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: yes invocation,  Prev: printf invocation,  Up: Printing text

15.3 `yes': Print a string until interrupted
============================================

`yes' prints the command line arguments, separated by spaces and
followed by a newline, forever until it is killed.  If no arguments are
given, it prints `y' followed by a newline forever until killed.

   Upon a write error, `yes' exits with status `1'.

   The only options are a lone `--help' or `--version'.  To output an
argument that begins with `-', precede it with `--', e.g., `yes --
--help'.  *Note Common options::.

File: coreutils.info,  Node: Conditions,  Next: Redirection,  Prev: Printing text,  Up: Top

16 Conditions
*************

This section describes commands that are primarily useful for their exit
status, rather than their output.  Thus, they are often used as the
condition of shell `if' statements, or as the last command in a
pipeline.

* Menu:

* false invocation::            Do nothing, unsuccessfully.
* true invocation::             Do nothing, successfully.
* test invocation::             Check file types and compare values.
* expr invocation::             Evaluate expressions.

File: coreutils.info,  Node: false invocation,  Next: true invocation,  Up: Conditions

16.1 `false': Do nothing, unsuccessfully
========================================

`false' does nothing except return an exit status of 1, meaning
"failure".  It can be used as a place holder in shell scripts where an
unsuccessful command is needed.  In most modern shells, `false' is a
built-in command, so when you use `false' in a script, you're probably
using the built-in command, not the one documented here.

   `false' honors the `--help' and `--version' options.

   This version of `false' is implemented as a C program, and is thus
more secure and faster than a shell script implementation, and may
safely be used as a dummy shell for the purpose of disabling accounts.

   Note that `false' (unlike all other programs documented herein)
exits unsuccessfully, even when invoked with `--help' or `--version'.

   Portable programs should not assume that the exit status of `false'
is 1, as it is greater than 1 on some non-GNU hosts.

File: coreutils.info,  Node: true invocation,  Next: test invocation,  Prev: false invocation,  Up: Conditions

16.2 `true': Do nothing, successfully
=====================================

`true' does nothing except return an exit status of 0, meaning
"success".  It can be used as a place holder in shell scripts where a
successful command is needed, although the shell built-in command `:'
(colon) may do the same thing faster.  In most modern shells, `true' is
a built-in command, so when you use `true' in a script, you're probably
using the built-in command, not the one documented here.

   `true' honors the `--help' and `--version' options.

   Note, however, that it is possible to cause `true' to exit with
nonzero status: with the `--help' or `--version' option, and with
standard output already closed or redirected to a file that evokes an
I/O error.  For example, using a Bourne-compatible shell:

     $ ./true --version >&-
     ./true: write error: Bad file number
     $ ./true --version > /dev/full
     ./true: write error: No space left on device

   This version of `true' is implemented as a C program, and is thus
more secure and faster than a shell script implementation, and may
safely be used as a dummy shell for the purpose of disabling accounts.

File: coreutils.info,  Node: test invocation,  Next: expr invocation,  Prev: true invocation,  Up: Conditions

16.3 `test': Check file types and compare values
================================================

`test' returns a status of 0 (true) or 1 (false) depending on the
evaluation of the conditional expression EXPR.  Each part of the
expression must be a separate argument.

   `test' has file status checks, string operators, and numeric
comparison operators.

   `test' has an alternate form that uses opening and closing square
brackets instead a leading `test'.  For example, instead of `test -d
/', you can write `[ -d / ]'.  The square brackets must be separate
arguments; for example, `[-d /]' does not have the desired effect.
Since `test EXPR' and `[ EXPR ]' have the same meaning, only the former
form is discussed below.

   Synopses:

     test EXPRESSION
     test
     [ EXPRESSION ]
     [ ]
     [ OPTION

   Due to shell aliases and built-in `test' command, using an unadorned
`test' interactively or in a script may get you different functionality
than that described here.  Invoke it via `env' (i.e., `env test ...')
to avoid interference from the shell.

   If EXPRESSION is omitted, `test' returns false.  If EXPRESSION is a
single argument, `test' returns false if the argument is null and true
otherwise.  The argument can be any string, including strings like
`-d', `-1', `--', `--help', and `--version' that most other programs
would treat as options.  To get help and version information, invoke
the commands `[ --help' and `[ --version', without the usual closing
brackets.  *Note Common options::.

   Exit status:

     0 if the expression is true,
     1 if the expression is false,
     2 if an error occurred.

* Menu:

* File type tests::             -[bcdfhLpSt]
* Access permission tests::     -[gkruwxOG]
* File characteristic tests::   -e -s -nt -ot -ef
* String tests::                -z -n = !=
* Numeric tests::               -eq -ne -lt -le -gt -ge
* Connectives for test::        ! -a -o

File: coreutils.info,  Node: File type tests,  Next: Access permission tests,  Up: test invocation

16.3.1 File type tests
----------------------

These options test for particular types of files.  (Everything's a file,
but not all files are the same!)

`-b FILE'
     True if FILE exists and is a block special device.

`-c FILE'
     True if FILE exists and is a character special device.

`-d FILE'
     True if FILE exists and is a directory.

`-f FILE'
     True if FILE exists and is a regular file.

`-h FILE'
`-L FILE'
     True if FILE exists and is a symbolic link.  Unlike all other
     file-related tests, this test does not dereference FILE if it is a
     symbolic link.

`-p FILE'
     True if FILE exists and is a named pipe.

`-S FILE'
     True if FILE exists and is a socket.

`-t FD'
     True if FD is a file descriptor that is associated with a terminal.


File: coreutils.info,  Node: Access permission tests,  Next: File characteristic tests,  Prev: File type tests,  Up: test invocation

16.3.2 Access permission tests
------------------------------

These options test for particular access permissions.

`-g FILE'
     True if FILE exists and has its set-group-ID bit set.

`-k FILE'
     True if FILE exists and has its "sticky" bit set.

`-r FILE'
     True if FILE exists and read permission is granted.

`-u FILE'
     True if FILE exists and has its set-user-ID bit set.

`-w FILE'
     True if FILE exists and write permission is granted.

`-x FILE'
     True if FILE exists and execute permission is granted (or search
     permission, if it is a directory).

`-O FILE'
     True if FILE exists and is owned by the current effective user ID.

`-G FILE'
     True if FILE exists and is owned by the current effective group ID.


File: coreutils.info,  Node: File characteristic tests,  Next: String tests,  Prev: Access permission tests,  Up: test invocation

16.3.3 File characteristic tests
--------------------------------

These options test other file characteristics.

`-e FILE'
     True if FILE exists.

`-s FILE'
     True if FILE exists and has a size greater than zero.

`FILE1 -nt FILE2'
     True if FILE1 is newer (according to modification date) than
     FILE2, or if FILE1 exists and FILE2 does not.

`FILE1 -ot FILE2'
     True if FILE1 is older (according to modification date) than
     FILE2, or if FILE2 exists and FILE1 does not.

`FILE1 -ef FILE2'
     True if FILE1 and FILE2 have the same device and inode numbers,
     i.e., if they are hard links to each other.


File: coreutils.info,  Node: String tests,  Next: Numeric tests,  Prev: File characteristic tests,  Up: test invocation

16.3.4 String tests
-------------------

These options test string characteristics.  You may need to quote
STRING arguments for the shell.  For example:

     test -n "$V"

   The quotes here prevent the wrong arguments from being passed to
`test' if `$V' is empty or contains special characters.

`-z STRING'
     True if the length of STRING is zero.

`-n STRING'
`STRING'
     True if the length of STRING is nonzero.

`STRING1 = STRING2'
     True if the strings are equal.

`STRING1 != STRING2'
     True if the strings are not equal.


File: coreutils.info,  Node: Numeric tests,  Next: Connectives for test,  Prev: String tests,  Up: test invocation

16.3.5 Numeric tests
--------------------

Numeric relational operators.  The arguments must be entirely numeric
(possibly negative), or the special expression `-l STRING', which
evaluates to the length of STRING.

`ARG1 -eq ARG2'
`ARG1 -ne ARG2'
`ARG1 -lt ARG2'
`ARG1 -le ARG2'
`ARG1 -gt ARG2'
`ARG1 -ge ARG2'
     These arithmetic binary operators return true if ARG1 is equal,
     not-equal, less-than, less-than-or-equal, greater-than, or
     greater-than-or-equal than ARG2, respectively.


   For example:

     test -1 -gt -2 && echo yes
     => yes
     test -l abc -gt 1 && echo yes
     => yes
     test 0x100 -eq 1
     error--> test: integer expression expected before -eq

File: coreutils.info,  Node: Connectives for test,  Prev: Numeric tests,  Up: test invocation

16.3.6 Connectives for `test'
-----------------------------

The usual logical connectives.

`! EXPR'
     True if EXPR is false.

`EXPR1 -a EXPR2'
     True if both EXPR1 and EXPR2 are true.

`EXPR1 -o EXPR2'
     True if either EXPR1 or EXPR2 is true.


File: coreutils.info,  Node: expr invocation,  Prev: test invocation,  Up: Conditions

16.4 `expr': Evaluate expressions
=================================

`expr' evaluates an expression and writes the result on standard
output.  Each token of the expression must be a separate argument.

   Operands are either integers or strings.  Integers consist of one or
more decimal digits, with an optional leading `-'.  `expr' converts
anything appearing in an operand position to an integer or a string
depending on the operation being applied to it.

   Strings are not quoted for `expr' itself, though you may need to
quote them to protect characters with special meaning to the shell,
e.g., spaces.  However, regardless of whether it is quoted, a string
operand should not be a parenthesis or any of `expr''s operators like
`+', so you cannot safely pass an arbitrary string `$str' to expr
merely by quoting it to the shell.  One way to work around this is to
use the GNU extension `+', (e.g., `+ "$str" = foo'); a more portable
way is to use `" $str"' and to adjust the rest of the expression to take
the leading space into account (e.g., `" $str" = " foo"').

   You should not pass a negative integer or a string with leading `-'
as `expr''s first argument, as it might be misinterpreted as an option;
this can be avoided by parenthesization.  Also, portable scripts should
not use a string operand that happens to take the form of an integer;
this can be worked around by inserting leading spaces as mentioned
above.

   Operators may be given as infix symbols or prefix keywords.
Parentheses may be used for grouping in the usual manner.  You must
quote parentheses and many operators to avoid the shell evaluating them,
however.

   When built with support for the GNU MP library, `expr' uses
arbitrary-precision arithmetic; otherwise, it uses native arithmetic
types and may fail due to arithmetic overflow.

   The only options are `--help' and `--version'.  *Note Common
options::.  Options must precede operands.

   Exit status:

     0 if the expression is neither null nor 0,
     1 if the expression is null or 0,
     2 if the expression is invalid,
     3 if an internal error occurred (e.g., arithmetic overflow).

* Menu:

* String expressions::          + : match substr index length
* Numeric expressions::         + - * / %
* Relations for expr::          | & < <= = == != >= >
* Examples of expr::            Examples.

File: coreutils.info,  Node: String expressions,  Next: Numeric expressions,  Up: expr invocation

16.4.1 String expressions
-------------------------

`expr' supports pattern matching and other string operators.  These
have higher precedence than both the numeric and relational operators
(in the next sections).

`STRING : REGEX'
     Perform pattern matching.  The arguments are converted to strings
     and the second is considered to be a (basic, a la GNU `grep')
     regular expression, with a `^' implicitly prepended.  The first
     argument is then matched against this regular expression.

     If the match succeeds and REGEX uses `\(' and `\)', the `:'
     expression returns the part of STRING that matched the
     subexpression; otherwise, it returns the number of characters
     matched.

     If the match fails, the `:' operator returns the null string if
     `\(' and `\)' are used in REGEX, otherwise 0.

     Only the first `\( ... \)' pair is relevant to the return value;
     additional pairs are meaningful only for grouping the regular
     expression operators.

     In the regular expression, `\+', `\?', and `\|' are operators
     which respectively match one or more, zero or one, or separate
     alternatives.  SunOS and other `expr''s treat these as regular
     characters.  (POSIX allows either behavior.)  *Note Regular
     Expression Library: (regex)Top, for details of regular expression
     syntax.  Some examples are in *note Examples of expr::.

`match STRING REGEX'
     An alternative way to do pattern matching.  This is the same as
     `STRING : REGEX'.

`substr STRING POSITION LENGTH'
     Returns the substring of STRING beginning at POSITION with length
     at most LENGTH.  If either POSITION or LENGTH is negative, zero,
     or non-numeric, returns the null string.

`index STRING CHARSET'
     Returns the first position in STRING where the first character in
     CHARSET was found.  If no character in CHARSET is found in STRING,
     return 0.

`length STRING'
     Returns the length of STRING.

`+ TOKEN'
     Interpret TOKEN as a string, even if it is a keyword like MATCH or
     an operator like `/'.  This makes it possible to test `expr length
     + "$x"' or `expr + "$x" : '.*/\(.\)'' and have it do the right
     thing even if the value of $X happens to be (for example) `/' or
     `index'.  This operator is a GNU extension.  Portable shell
     scripts should use `" $token" : ' \(.*\)'' instead of `+ "$token"'.


   To make `expr' interpret keywords as strings, you must use the
`quote' operator.

File: coreutils.info,  Node: Numeric expressions,  Next: Relations for expr,  Prev: String expressions,  Up: expr invocation

16.4.2 Numeric expressions
--------------------------

`expr' supports the usual numeric operators, in order of increasing
precedence.  These numeric operators have lower precedence than the
string operators described in the previous section, and higher
precedence than the connectives (next section).

`+ -'
     Addition and subtraction.  Both arguments are converted to
     integers; an error occurs if this cannot be done.

`* / %'
     Multiplication, division, remainder.  Both arguments are converted
     to integers; an error occurs if this cannot be done.


File: coreutils.info,  Node: Relations for expr,  Next: Examples of expr,  Prev: Numeric expressions,  Up: expr invocation

16.4.3 Relations for `expr'
---------------------------

`expr' supports the usual logical connectives and relations.  These
have lower precedence than the string and numeric operators (previous
sections).  Here is the list, lowest-precedence operator first.

`|'
     Returns its first argument if that is neither null nor zero,
     otherwise its second argument if it is neither null nor zero,
     otherwise 0.  It does not evaluate its second argument if its
     first argument is neither null nor zero.

`&'
     Return its first argument if neither argument is null or zero,
     otherwise 0.  It does not evaluate its second argument if its
     first argument is null or zero.

`< <= = == != >= >'
     Compare the arguments and return 1 if the relation is true, 0
     otherwise.  `==' is a synonym for `='.  `expr' first tries to
     convert both arguments to integers and do a numeric comparison; if
     either conversion fails, it does a lexicographic comparison using
     the character collating sequence specified by the `LC_COLLATE'
     locale.


File: coreutils.info,  Node: Examples of expr,  Prev: Relations for expr,  Up: expr invocation

16.4.4 Examples of using `expr'
-------------------------------

Here are a few examples, including quoting for shell metacharacters.

   To add 1 to the shell variable `foo', in Bourne-compatible shells:

     foo=`expr $foo + 1`

   To print the non-directory part of the file name stored in `$fname',
which need not contain a `/':

     expr $fname : '.*/\(.*\)' '|' $fname

   An example showing that `\+' is an operator:

     expr aaa : 'a\+'
     => 3

     expr abc : 'a\(.\)c'
     => b
     expr index abcdef cz
     => 3
     expr index index a
     error--> expr: syntax error
     expr index + index a
     => 0

File: coreutils.info,  Node: Redirection,  Next: File name manipulation,  Prev: Conditions,  Up: Top

17 Redirection
**************

Unix shells commonly provide several forms of "redirection"--ways to
change the input source or output destination of a command.  But one
useful redirection is performed by a separate command, not by the shell;
it's described here.

* Menu:

* tee invocation::              Redirect output to multiple files or processes.

File: coreutils.info,  Node: tee invocation,  Up: Redirection

17.1 `tee': Redirect output to multiple files or processes
==========================================================

The `tee' command copies standard input to standard output and also to
any files given as arguments.  This is useful when you want not only to
send some data down a pipe, but also to save a copy.  Synopsis:

     tee [OPTION]... [FILE]...

   If a file being written to does not already exist, it is created.
If a file being written to already exists, the data it previously
contained is overwritten unless the `-a' option is used.

   A FILE of `-' causes `tee' to send another copy of input to standard
output, but this is typically not that useful as the copies are
interleaved.

   The program accepts the following options.  Also see *note Common
options::.

`-a'
`--append'
     Append standard input to the given files rather than overwriting
     them.

`-i'
`--ignore-interrupts'
     Ignore interrupt signals.


   The `tee' command is useful when you happen to be transferring a
large amount of data and also want to summarize that data without
reading it a second time.  For example, when you are downloading a DVD
image, you often want to verify its signature or checksum right away.
The inefficient way to do it is simply:

     wget http://example.com/some.iso && sha1sum some.iso

   One problem with the above is that it makes you wait for the
download to complete before starting the time-consuming SHA1
computation.  Perhaps even more importantly, the above requires reading
the DVD image a second time (the first was from the network).

   The efficient way to do it is to interleave the download and SHA1
computation.  Then, you'll get the checksum for free, because the
entire process parallelizes so well:

     # slightly contrived, to demonstrate process substitution
     wget -O - http://example.com/dvd.iso \
       | tee >(sha1sum > dvd.sha1) > dvd.iso

   That makes `tee' write not just to the expected output file, but
also to a pipe running `sha1sum' and saving the final checksum in a
file named `dvd.sha1'.

   Note, however, that this example relies on a feature of modern shells
called "process substitution" (the `>(command)' syntax, above; *Note
Process Substitution: (bashref)Process Substitution.), so it works with
`zsh', `bash', and `ksh', but not with `/bin/sh'.  So if you write code
like this in a shell script, be sure to start the script with
`#!/bin/bash'.

   Since the above example writes to one file and one process, a more
conventional and portable use of `tee' is even better:

     wget -O - http://example.com/dvd.iso \
       | tee dvd.iso | sha1sum > dvd.sha1

   You can extend this example to make `tee' write to two processes,
computing MD5 and SHA1 checksums in parallel.  In this case, process
substitution is required:

     wget -O - http://example.com/dvd.iso \
       | tee >(sha1sum > dvd.sha1) \
             >(md5sum > dvd.md5) \
       > dvd.iso

   This technique is also useful when you want to make a _compressed_
copy of the contents of a pipe.  Consider a tool to graphically
summarize disk usage data from `du -ak'.  For a large hierarchy, `du
-ak' can run for a long time, and can easily produce terabytes of data,
so you won't want to rerun the command unnecessarily.  Nor will you
want to save the uncompressed output.

   Doing it the inefficient way, you can't even start the GUI until
after you've compressed all of the `du' output:

     du -ak | gzip -9 > /tmp/du.gz
     gzip -d /tmp/du.gz | xdiskusage -a

   With `tee' and process substitution, you start the GUI right away
and eliminate the decompression completely:

     du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a

   Finally, if you regularly create more than one type of compressed
tarball at once, for example when `make dist' creates both
`gzip'-compressed and `bzip2'-compressed tarballs, there may be a
better way.  Typical `automake'-generated `Makefile' rules create the
two compressed tar archives with commands in sequence, like this
(slightly simplified):

     tardir=your-pkg-M.N
     tar chof - "$tardir" | gzip  -9 -c > your-pkg-M.N.tar.gz
     tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2

   However, if the hierarchy you are archiving and compressing is larger
than a couple megabytes, and especially if you are using a
multi-processor system with plenty of memory, then you can do much
better by reading the directory contents only once and running the
compression programs in parallel:

     tardir=your-pkg-M.N
     tar chof - "$tardir" \
       | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
       | bzip2 -9 -c > your-pkg-M.N.tar.bz2

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: File name manipulation,  Next: Working context,  Prev: Redirection,  Up: Top

18 File name manipulation
*************************

This section describes commands that manipulate file names.

* Menu:

* basename invocation::         Strip directory and suffix from a file name.
* dirname invocation::          Strip non-directory suffix from a file name.
* pathchk invocation::          Check file name validity and portability.
* mktemp invocation::           Create temporary file or directory.

File: coreutils.info,  Node: basename invocation,  Next: dirname invocation,  Up: File name manipulation

18.1 `basename': Strip directory and suffix from a file name
============================================================

`basename' removes any leading directory components from NAME.
Synopsis:

     basename NAME [SUFFIX]

   If SUFFIX is specified and is identical to the end of NAME, it is
removed from NAME as well.  Note that since trailing slashes are
removed prior to suffix matching, SUFFIX will do nothing if it contains
slashes.  `basename' prints the result on standard output.

   Together, `basename' and `dirname' are designed such that if `ls
"$name"' succeeds, then the command sequence `cd "$(dirname "$name")";
ls "$(basename "$name")"' will, too.  This works for everything except
file names containing a trailing newline.

   POSIX allows the implementation to define the results if NAME is
empty or `//'.  In the former case, GNU `basename' returns the empty
string.  In the latter case, the result is `//' on platforms where //
is distinct from /, and `/' on platforms where there is no difference.

   The only options are `--help' and `--version'.  *Note Common
options::.  Options must precede operands.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Examples:

     # Output "sort".
     basename /usr/bin/sort

     # Output "stdio".
     basename include/stdio.h .h

File: coreutils.info,  Node: dirname invocation,  Next: pathchk invocation,  Prev: basename invocation,  Up: File name manipulation

18.2 `dirname': Strip non-directory suffix from a file name
===========================================================

`dirname' prints all but the final slash-delimited component of a
string (presumably a file name).  Synopsis:

     dirname NAME

   If NAME is a single component, `dirname' prints `.' (meaning the
current directory).

   Together, `basename' and `dirname' are designed such that if `ls
"$name"' succeeds, then the command sequence `cd "$(dirname "$name")";
ls "$(basename "$name")"' will, too.  This works for everything except
file names containing a trailing newline.

   POSIX allows the implementation to define the results if NAME is
`//'.  With GNU `dirname', the result is `//' on platforms where // is
distinct from /, and `/' on platforms where there is no difference.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Examples:

     # Output "/usr/bin".
     dirname /usr/bin/sort

     # Output ".".
     dirname stdio.h

File: coreutils.info,  Node: pathchk invocation,  Next: mktemp invocation,  Prev: dirname invocation,  Up: File name manipulation

18.3 `pathchk': Check file name validity and portability
========================================================

`pathchk' checks validity and portability of file names.  Synopsis:

     pathchk [OPTION]... NAME...

   For each NAME, `pathchk' prints an error message if any of these
conditions is true:

  1. One of the existing directories in NAME does not have search
     (execute) permission,

  2. The length of NAME is larger than the maximum supported by the
     operating system.

  3. The length of one component of NAME is longer than its file
     system's maximum.

   A nonexistent NAME is not an error, so long a file with that name
could be created under the above conditions.

   The program accepts the following options.  Also see *note Common
options::.  Options must precede operands.

`-p'
     Instead of performing checks based on the underlying file system,
     print an error message if any of these conditions is true:

       1. A file name is empty.

       2. A file name contains a character outside the POSIX portable
          file name character set, namely, the ASCII letters and
          digits, `.', `_', `-', and `/'.

       3. The length of a file name or one of its components exceeds the
          POSIX minimum limits for portability.

`-P'
     Print an error message if a file name is empty, or if it contains
     a component that begins with `-'.

`--portability'
     Print an error message if a file name is not portable to all POSIX
     hosts.  This option is equivalent to `-p -P'.


   Exit status:

     0 if all specified file names passed all checks,
     1 otherwise.

File: coreutils.info,  Node: mktemp invocation,  Prev: pathchk invocation,  Up: File name manipulation

18.4 `mktemp': Create temporary file or directory
=================================================

`mktemp' manages the creation of temporary files and directories.
Synopsis:

     mktemp [OPTION]... [TEMPLATE]

   Safely create a temporary file or directory based on TEMPLATE, and
print its name.  If given, TEMPLATE must include at least three
consecutive `X's in the last component.  If omitted, the template
`tmp.XXXXXXXXXX' is used, and option `--tmpdir' is implied.  The final
run of `X's in the TEMPLATE will be replaced by alpha-numeric
characters; thus, on a case-sensitive file system, and with a TEMPLATE
including a run of N instances of `X', there are `62**N' potential file
names.

   Older scripts used to create temporary files by simply joining the
name of the program with the process id (`$$') as a suffix.  However,
that naming scheme is easily predictable, and suffers from a race
condition where the attacker can create an appropriately named symbolic
link, such that when the script then opens a handle to what it thought
was an unused file, it is instead modifying an existing file.  Using
the same scheme to create a directory is slightly safer, since the
`mkdir' will fail if the target already exists, but it is still
inferior because it allows for denial of service attacks.  Therefore,
modern scripts should use the `mktemp' command to guarantee that the
generated name will be unpredictable, and that knowledge of the
temporary file name implies that the file was created by the current
script and cannot be modified by other users.

   When creating a file, the resulting file has read and write
permissions for the current user, but no permissions for the group or
others; these permissions are reduced if the current umask is more
restrictive.

   Here are some examples (although note that if you repeat them, you
will most likely get different file names):

   * Create a temporary file in the current directory.
          $ mktemp file.XXXX
          file.H47c

   * Create a temporary file with a known suffix.
          $ mktemp --suffix=.txt file-XXXX
          file-H08W.txt
          $ mktemp file-XXXX-XXXX.txt
          file-XXXX-eI9L.txt

   * Create a secure fifo relative to the user's choice of `TMPDIR',
     but falling back to the current directory rather than `/tmp'.
     Note that `mktemp' does not create fifos, but can create a secure
     directory in which the fifo can live.  Exit the shell if the
     directory or fifo could not be created.
          $ dir=$(mktemp -p "${TMPDIR:-.}" -d dir-XXXX) || exit 1
          $ fifo=$dir/fifo
          $ mkfifo "$fifo" || { rmdir "$dir"; exit 1; }

   * Create and use a temporary file if possible, but ignore failure.
     The file will reside in the directory named by `TMPDIR', if
     specified, or else in `/tmp'.
          $ file=$(mktemp -q) && {
          >   # Safe to use $file only within this block.  Use quotes,
          >   # since $TMPDIR, and thus $file, may contain whitespace.
          >   echo ... > "$file"
          >   rm "$file"
          > }

   * Act as a semi-random character generator (it is not fully random,
     since it is impacted by the contents of the current directory).  To
     avoid security holes, do not use the resulting names to create a
     file.
          $ mktemp -u XXX
          Gb9
          $ mktemp -u XXX
          nzC


   The program accepts the following options.  Also see *note Common
options::.

`-d'
`--directory'
     Create a directory rather than a file.  The directory will have
     read, write, and search permissions for the current user, but no
     permissions for the group or others; these permissions are reduced
     if the current umask is more restrictive.

`-q'
`--quiet'
     Suppress diagnostics about failure to create a file or directory.
     The exit status will still reflect whether a file was created.

`-u'
`--dry-run'
     Generate a temporary name that does not name an existing file,
     without changing the file system contents.  Using the output of
     this command to create a new file is inherently unsafe, as there
     is a window of time between generating the name and using it where
     another process can create an object by the same name.

`-p DIR'
`--tmpdir[=DIR]'
     Treat TEMPLATE relative to the directory DIR.  If DIR is not
     specified (only possible with the long option `--tmpdir') or is
     the empty string, use the value of `TMPDIR' if available,
     otherwise use `/tmp'.  If this is specified, TEMPLATE must not be
     absolute.  However, TEMPLATE can still contain slashes, although
     intermediate directories must already exist.

`--suffix=SUFFIX'
     Append SUFFIX to the TEMPLATE.  SUFFIX must not contain slash.  If
     `--suffix' is specified, TEMPLATE must end in `X'; if it is not
     specified, then an appropriate `--suffix' is inferred by finding
     the last `X' in TEMPLATE.  This option exists for use with the
     default TEMPLATE and for the creation of a SUFFIX that starts with
     `X'.

`-t'
     Treat TEMPLATE as a single file relative to the value of `TMPDIR'
     if available, or to the directory specified by `-p', otherwise to
     `/tmp'.  TEMPLATE must not contain slashes.  This option is
     deprecated; the use of `-p' without `-t' offers better defaults
     (by favoring the command line over `TMPDIR') and more flexibility
     (by allowing intermediate directories).


   Exit status:

     0 if the file was created,
     1 otherwise.

File: coreutils.info,  Node: Working context,  Next: User information,  Prev: File name manipulation,  Up: Top

19 Working context
******************

This section describes commands that display or alter the context in
which you are working: the current directory, the terminal settings, and
so forth.  See also the user-related commands in the next section.

* Menu:

* pwd invocation::              Print working directory.
* stty invocation::             Print or change terminal characteristics.
* printenv invocation::         Print environment variables.
* tty invocation::              Print file name of terminal on standard input.

File: coreutils.info,  Node: pwd invocation,  Next: stty invocation,  Up: Working context

19.1 `pwd': Print working directory
===================================

`pwd' prints the name of the current directory.  Synopsis:

     pwd [OPTION]...

   The program accepts the following options.  Also see *note Common
options::.

`-L'
`--logical'
     If the contents of the environment variable `PWD' provide an
     absolute name of the current directory with no `.' or `..'
     components, but possibly with symbolic links, then output those
     contents.  Otherwise, fall back to default `-P' handling.

`-P'
`--physical'
     Print a fully resolved name for the current directory.  That is,
     all components of the printed name will be actual directory
     names--none will be symbolic links.

   If `-L' and `-P' are both given, the last one takes precedence.  If
neither option is given, then this implementation uses `-P' as the
default unless the `POSIXLY_CORRECT' environment variable is set.

   Due to shell aliases and built-in `pwd' command, using an unadorned
`pwd' interactively or in a script may get you different functionality
than that described here.  Invoke it via `env' (i.e., `env pwd ...') to
avoid interference from the shell.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: stty invocation,  Next: printenv invocation,  Prev: pwd invocation,  Up: Working context

19.2 `stty': Print or change terminal characteristics
=====================================================

`stty' prints or changes terminal characteristics, such as baud rate.
Synopses:

     stty [OPTION] [SETTING]...
     stty [OPTION]

   If given no line settings, `stty' prints the baud rate, line
discipline number (on systems that support it), and line settings that
have been changed from the values set by `stty sane'.  By default, mode
reading and setting are performed on the tty line connected to standard
input, although this can be modified by the `--file' option.

   `stty' accepts many non-option arguments that change aspects of the
terminal line operation, as described below.

   The program accepts the following options.  Also see *note Common
options::.

`-a'
`--all'
     Print all current settings in human-readable form.  This option
     may not be used in combination with any line settings.

`-F DEVICE'
`--file=DEVICE'
     Set the line opened by the file name specified in DEVICE instead of
     the tty line connected to standard input.  This option is necessary
     because opening a POSIX tty requires use of the `O_NONDELAY' flag
     to prevent a POSIX tty from blocking until the carrier detect line
     is high if the `clocal' flag is not set.  Hence, it is not always
     possible to allow the shell to open the device in the traditional
     manner.

`-g'
`--save'
     Print all current settings in a form that can be used as an
     argument to another `stty' command to restore the current
     settings.  This option may not be used in combination with any
     line settings.


   Many settings can be turned off by preceding them with a `-'.  Such
arguments are marked below with "May be negated" in their description.
The descriptions themselves refer to the positive case, that is, when
_not_ negated (unless stated otherwise, of course).

   Some settings are not available on all POSIX systems, since they use
extensions.  Such arguments are marked below with "Non-POSIX" in their
description.  On non-POSIX systems, those or other settings also may not
be available, but it's not feasible to document all the variations: just
try it and see.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

* Menu:

* Control::                     Control settings
* Input::                       Input settings
* Output::                      Output settings
* Local::                       Local settings
* Combination::                 Combination settings
* Characters::                  Special characters
* Special::                     Special settings

File: coreutils.info,  Node: Control,  Next: Input,  Up: stty invocation

19.2.1 Control settings
-----------------------

Control settings:

`parenb'
     Generate parity bit in output and expect parity bit in input.  May
     be negated.

`parodd'
     Set odd parity (even if negated).  May be negated.

`cs5'
`cs6'
`cs7'
`cs8'
     Set character size to 5, 6, 7, or 8 bits.

`hup'
`hupcl'
     Send a hangup signal when the last process closes the tty.  May be
     negated.

`cstopb'
     Use two stop bits per character (one if negated).  May be negated.

`cread'
     Allow input to be received.  May be negated.

`clocal'
     Disable modem control signals.  May be negated.

`crtscts'
     Enable RTS/CTS flow control.  Non-POSIX.  May be negated.

`cdtrdsr'
     Enable DTR/DSR flow control. Non-POSIX.  May be negated.

File: coreutils.info,  Node: Input,  Next: Output,  Prev: Control,  Up: stty invocation

19.2.2 Input settings
---------------------

These settings control operations on data received from the terminal.

`ignbrk'
     Ignore break characters.  May be negated.

`brkint'
     Make breaks cause an interrupt signal.  May be negated.

`ignpar'
     Ignore characters with parity errors.  May be negated.

`parmrk'
     Mark parity errors (with a 255-0-character sequence).  May be
     negated.

`inpck'
     Enable input parity checking.  May be negated.

`istrip'
     Clear high (8th) bit of input characters.  May be negated.

`inlcr'
     Translate newline to carriage return.  May be negated.

`igncr'
     Ignore carriage return.  May be negated.

`icrnl'
     Translate carriage return to newline.  May be negated.

`iutf8'
     Assume input characters are UTF-8 encoded.  May be negated.

`ixon'
     Enable XON/XOFF flow control (that is, `CTRL-S'/`CTRL-Q').  May be
     negated.

`ixoff'
`tandem'
     Enable sending of `stop' character when the system input buffer is
     almost full, and `start' character when it becomes almost empty
     again.  May be negated.

`iuclc'
     Translate uppercase characters to lowercase.  Non-POSIX.  May be
     negated. Note ilcuc is not implemented, as one would not be able
     to issue almost any (lowercase) Unix command, after invoking it.

`ixany'
     Allow any character to restart output (only the start character if
     negated).  Non-POSIX.  May be negated.

`imaxbel'
     Enable beeping and not flushing input buffer if a character arrives
     when the input buffer is full.  Non-POSIX.  May be negated.

File: coreutils.info,  Node: Output,  Next: Local,  Prev: Input,  Up: stty invocation

19.2.3 Output settings
----------------------

These settings control operations on data sent to the terminal.

`opost'
     Postprocess output.  May be negated.

`olcuc'
     Translate lowercase characters to uppercase.  Non-POSIX.  May be
     negated. (Note ouclc is not currently implemented.)

`ocrnl'
     Translate carriage return to newline.  Non-POSIX.  May be negated.

`onlcr'
     Translate newline to carriage return-newline.  Non-POSIX.  May be
     negated.

`onocr'
     Do not print carriage returns in the first column.  Non-POSIX.
     May be negated.

`onlret'
     Newline performs a carriage return.  Non-POSIX.  May be negated.

`ofill'
     Use fill (padding) characters instead of timing for delays.
     Non-POSIX.  May be negated.

`ofdel'
     Use ASCII DEL characters for fill instead of ASCII NUL characters.
     Non-POSIX.  May be negated.

`nl1'
`nl0'
     Newline delay style.  Non-POSIX.

`cr3'
`cr2'
`cr1'
`cr0'
     Carriage return delay style.  Non-POSIX.

`tab3'
`tab2'
`tab1'
`tab0'
     Horizontal tab delay style.  Non-POSIX.

`bs1'
`bs0'
     Backspace delay style.  Non-POSIX.

`vt1'
`vt0'
     Vertical tab delay style.  Non-POSIX.

`ff1'
`ff0'
     Form feed delay style.  Non-POSIX.

File: coreutils.info,  Node: Local,  Next: Combination,  Prev: Output,  Up: stty invocation

19.2.4 Local settings
---------------------

`isig'
     Enable `interrupt', `quit', and `suspend' special characters.  May
     be negated.

`icanon'
     Enable `erase', `kill', `werase', and `rprnt' special characters.
     May be negated.

`iexten'
     Enable non-POSIX special characters.  May be negated.

`echo'
     Echo input characters.  May be negated.

`echoe'
`crterase'
     Echo `erase' characters as backspace-space-backspace.  May be
     negated.

`echok'
     Echo a newline after a `kill' character.  May be negated.

`echonl'
     Echo newline even if not echoing other characters.  May be negated.

`noflsh'
     Disable flushing after `interrupt' and `quit' special characters.
     May be negated.

`xcase'
     Enable input and output of uppercase characters by preceding their
     lowercase equivalents with `\', when `icanon' is set.  Non-POSIX.
     May be negated.

`tostop'
     Stop background jobs that try to write to the terminal.  Non-POSIX.
     May be negated.

`echoprt'
`prterase'
     Echo erased characters backward, between `\' and `/'.  Non-POSIX.
     May be negated.

`echoctl'
`ctlecho'
     Echo control characters in hat notation (`^C') instead of
     literally.  Non-POSIX.  May be negated.

`echoke'
`crtkill'
     Echo the `kill' special character by erasing each character on the
     line as indicated by the `echoprt' and `echoe' settings, instead
     of by the `echoctl' and `echok' settings.  Non-POSIX.  May be
     negated.

File: coreutils.info,  Node: Combination,  Next: Characters,  Prev: Local,  Up: stty invocation

19.2.5 Combination settings
---------------------------

Combination settings:

`evenp'
`parity'
     Same as `parenb -parodd cs7'.  May be negated.  If negated, same
     as `-parenb cs8'.

`oddp'
     Same as `parenb parodd cs7'.  May be negated.  If negated, same as
     `-parenb cs8'.

`nl'
     Same as `-icrnl -onlcr'.  May be negated.  If negated, same as
     `icrnl -inlcr -igncr onlcr -ocrnl -onlret'.

`ek'
     Reset the `erase' and `kill' special characters to their default
     values.

`sane'
     Same as:

          cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
          -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
          -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
          ff0 isig icanon iexten echo echoe echok -echonl
          -noflsh -xcase -tostop -echoprt echoctl echoke

     and also sets all special characters to their default values.

`cooked'
     Same as `brkint ignpar istrip icrnl ixon opost isig icanon', plus
     sets the `eof' and `eol' characters to their default values if
     they are the same as the `min' and `time' characters.  May be
     negated.  If negated, same as `raw'.

`raw'
     Same as:

          -ignbrk -brkint -ignpar -parmrk -inpck -istrip
          -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
          -imaxbel -opost -isig -icanon -xcase min 1 time 0

     May be negated.  If negated, same as `cooked'.

`cbreak'
     Same as `-icanon'.  May be negated.  If negated, same as `icanon'.

`pass8'
     Same as `-parenb -istrip cs8'.  May be negated.  If negated, same
     as `parenb istrip cs7'.

`litout'
     Same as `-parenb -istrip -opost cs8'.  May be negated.  If
     negated, same as `parenb istrip opost cs7'.

`decctlq'
     Same as `-ixany'.  Non-POSIX.  May be negated.

`tabs'
     Same as `tab0'.  Non-POSIX.  May be negated.  If negated, same as
     `tab3'.

`lcase'
`LCASE'
     Same as `xcase iuclc olcuc'.  Non-POSIX.  May be negated.  (Used
     for terminals with uppercase characters only.)

`crt'
     Same as `echoe echoctl echoke'.

`dec'
     Same as `echoe echoctl echoke -ixany intr ^C erase ^? kill C-u'.

File: coreutils.info,  Node: Characters,  Next: Special,  Prev: Combination,  Up: stty invocation

19.2.6 Special characters
-------------------------

The special characters' default values vary from system to system.
They are set with the syntax `name value', where the names are listed
below and the value can be given either literally, in hat notation
(`^C'), or as an integer which may start with `0x' to indicate
hexadecimal, `0' to indicate octal, or any other digit to indicate
decimal.

   For GNU stty, giving a value of `^-' or `undef' disables that
special character.  (This is incompatible with Ultrix `stty', which
uses  a value of `u' to disable a special character.  GNU `stty' treats
a value `u' like any other, namely to set that special character to
<U>.)

`intr'
     Send an interrupt signal.

`quit'
     Send a quit signal.

`erase'
     Erase the last character typed.

`kill'
     Erase the current line.

`eof'
     Send an end of file (terminate the input).

`eol'
     End the line.

`eol2'
     Alternate character to end the line.  Non-POSIX.

`swtch'
     Switch to a different shell layer.  Non-POSIX.

`start'
     Restart the output after stopping it.

`stop'
     Stop the output.

`susp'
     Send a terminal stop signal.

`dsusp'
     Send a terminal stop signal after flushing the input.  Non-POSIX.

`rprnt'
     Redraw the current line.  Non-POSIX.

`werase'
     Erase the last word typed.  Non-POSIX.

`lnext'
     Enter the next character typed literally, even if it is a special
     character.  Non-POSIX.

File: coreutils.info,  Node: Special,  Prev: Characters,  Up: stty invocation

19.2.7 Special settings
-----------------------

`min N'
     Set the minimum number of characters that will satisfy a read until
     the time value has expired, when `-icanon' is set.

`time N'
     Set the number of tenths of a second before reads time out if the
     minimum number of characters have not been read, when `-icanon' is
     set.

`ispeed N'
     Set the input speed to N.

`ospeed N'
     Set the output speed to N.

`rows N'
     Tell the tty kernel driver that the terminal has N rows.
     Non-POSIX.

`cols N'
`columns N'
     Tell the kernel that the terminal has N columns.  Non-POSIX.

`size'
     Print the number of rows and columns that the kernel thinks the
     terminal has.  (Systems that don't support rows and columns in the
     kernel typically use the environment variables `LINES' and
     `COLUMNS' instead; however, GNU `stty' does not know anything
     about them.)  Non-POSIX.

`line N'
     Use line discipline N.  Non-POSIX.

`speed'
     Print the terminal speed.

`N'
     Set the input and output speeds to N.  N can be one of: 0 50 75
     110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200 38400
     `exta' `extb'.  `exta' is the same as 19200; `extb' is the same as
     38400.  Many systems, including GNU/Linux, support higher speeds.
     The `stty' command includes support for speeds of 57600, 115200,
     230400, 460800, 500000, 576000, 921600, 1000000, 1152000, 1500000,
     2000000, 2500000, 3000000, 3500000, or 4000000 where the system
     supports these.  0 hangs up the line if `-clocal' is set.

File: coreutils.info,  Node: printenv invocation,  Next: tty invocation,  Prev: stty invocation,  Up: Working context

19.3 `printenv': Print all or some environment variables
========================================================

`printenv' prints environment variable values.  Synopsis:

     printenv [OPTION] [VARIABLE]...

   If no VARIABLEs are specified, `printenv' prints the value of every
environment variable.  Otherwise, it prints the value of each VARIABLE
that is set, and nothing for those that are not set.

   The program accepts the following option.  Also see *note Common
options::.

`-0'
`--null'
     Output a zero byte (ASCII NUL) at the end of each line, rather
     than a newline. This option enables other programs to parse the
     output of `printenv' even when that output would contain data with
     embedded newlines.


   Exit status:

     0 if all variables specified were found
     1 if at least one specified variable was not found
     2 if a write error occurred

File: coreutils.info,  Node: tty invocation,  Prev: printenv invocation,  Up: Working context

19.4 `tty': Print file name of terminal on standard input
=========================================================

`tty' prints the file name of the terminal connected to its standard
input.  It prints `not a tty' if standard input is not a terminal.
Synopsis:

     tty [OPTION]...

   The program accepts the following option.  Also see *note Common
options::.

`-s'
`--silent'
`--quiet'
     Print nothing; only return an exit status.


   Exit status:

     0 if standard input is a terminal
     1 if standard input is not a terminal
     2 if given incorrect arguments
     3 if a write error occurs

File: coreutils.info,  Node: User information,  Next: System context,  Prev: Working context,  Up: Top

20 User information
*******************

This section describes commands that print user-related information:
logins, groups, and so forth.

* Menu:

* id invocation::               Print user identity.
* logname invocation::          Print current login name.
* whoami invocation::           Print effective user ID.
* groups invocation::           Print group names a user is in.
* users invocation::            Print login names of users currently logged in.
* who invocation::              Print who is currently logged in.

File: coreutils.info,  Node: id invocation,  Next: logname invocation,  Up: User information

20.1 `id': Print user identity
==============================

`id' prints information about the given user, or the process running it
if no user is specified.  Synopsis:

     id [OPTION]... [USERNAME]

   By default, it prints the real user ID, real group ID, effective
user ID if different from the real user ID, effective group ID if
different from the real group ID, and supplemental group IDs.  In
addition, if SELinux is enabled and the `POSIXLY_CORRECT' environment
variable is not set, then print `context=C', where C is the security
context.

   Each of these numeric values is preceded by an identifying string and
followed by the corresponding user or group name in parentheses.

   The options cause `id' to print only part of the above information.
Also see *note Common options::.

`-g'
`--group'
     Print only the group ID.

`-G'
`--groups'
     Print only the group ID and the supplementary groups.

`-n'
`--name'
     Print the user or group name instead of the ID number.  Requires
     `-u', `-g', or `-G'.

`-r'
`--real'
     Print the real, instead of effective, user or group ID.  Requires
     `-u', `-g', or `-G'.

`-u'
`--user'
     Print only the user ID.

`-Z'
`--context'
     Print only the security context of the current user.  If SELinux
     is disabled then print a warning and set the exit status to 1.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Primary and supplementary groups for a process are normally inherited
from its parent and are usually unchanged since login.  This means that
if you change the group database after logging in, `id' will not
reflect your changes within your existing login session.  Running `id'
with a user argument causes the user and group database to be consulted
afresh, and so will give a different result.

File: coreutils.info,  Node: logname invocation,  Next: whoami invocation,  Prev: id invocation,  Up: User information

20.2 `logname': Print current login name
========================================

`logname' prints the calling user's name, as found in a
system-maintained file (often `/var/run/utmp' or `/var/run/utmp'), and
exits with a status of 0.  If there is no entry for the calling
process, `logname' prints an error message and exits with a status of 1.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: whoami invocation,  Next: groups invocation,  Prev: logname invocation,  Up: User information

20.3 `whoami': Print effective user ID
======================================

`whoami' prints the user name associated with the current effective
user ID.  It is equivalent to the command `id -un'.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: groups invocation,  Next: users invocation,  Prev: whoami invocation,  Up: User information

20.4 `groups': Print group names a user is in
=============================================

`groups' prints the names of the primary and any supplementary groups
for each given USERNAME, or the current process if no names are given.
If more than one name is given, the name of each user is printed before
the list of that user's groups and the user name is separated from the
group list by a colon.  Synopsis:

     groups [USERNAME]...

   The group lists are equivalent to the output of the command `id -Gn'.

   Primary and supplementary groups for a process are normally inherited
from its parent and are usually unchanged since login.  This means that
if you change the group database after logging in, `groups' will not
reflect your changes within your existing login session.  Running
`groups' with a list of users causes the user and group database to be
consulted afresh, and so will give a different result.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: users invocation,  Next: who invocation,  Prev: groups invocation,  Up: User information

20.5 `users': Print login names of users currently logged in
============================================================

`users' prints on a single line a blank-separated list of user names of
users currently logged in to the current host.  Each user name
corresponds to a login session, so if a user has more than one login
session, that user's name will appear the same number of times in the
output.  Synopsis:

     users [FILE]

   With no FILE argument, `users' extracts its information from a
system-maintained file (often `/var/run/utmp' or `/var/run/utmp').  If
a file argument is given, `users' uses that file instead.  A common
choice is `/var/log/wtmp'.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: who invocation,  Prev: users invocation,  Up: User information

20.6 `who': Print who is currently logged in
============================================

`who' prints information about users who are currently logged on.
Synopsis:

     `who' [OPTION] [FILE] [am i]

   If given no non-option arguments, `who' prints the following
information for each user currently logged on: login name, terminal
line, login time, and remote hostname or X display.

   If given one non-option argument, `who' uses that instead of a
default system-maintained file (often `/var/run/utmp' or
`/var/run/utmp') as the name of the file containing the record of users
logged on.  `/var/log/wtmp' is commonly given as an argument to `who'
to look at who has previously logged on.

   If given two non-option arguments, `who' prints only the entry for
the user running it (determined from its standard input), preceded by
the hostname.  Traditionally, the two arguments given are `am i', as in
`who am i'.

   Time stamps are listed according to the time zone rules specified by
the `TZ' environment variable, or by the system default rules if `TZ'
is not set.  *Note Specifying the Time Zone with `TZ': (libc)TZ
Variable.

   The program accepts the following options.  Also see *note Common
options::.

`-a'
`--all'
     Same as `-b -d --login -p -r -t -T -u'.

`-b'
`--boot'
     Print the date and time of last system boot.

`-d'
`--dead'
     Print information corresponding to dead processes.

`-H'
`--heading'
     Print a line of column headings.

`-l'
`--login'
     List only the entries that correspond to processes via which the
     system is waiting for a user to login.  The user name is always
     `LOGIN'.

`--lookup'
     Attempt to canonicalize hostnames found in utmp through a DNS
     lookup.  This is not the default because it can cause significant
     delays on systems with automatic dial-up internet access.

`-m'
     Same as `who am i'.

`-p'
`--process'
     List active processes spawned by init.

`-q'
`--count'
     Print only the login names and the number of users logged on.
     Overrides all other options.

`-r'
`--runlevel'
     Print the current (and maybe previous) run-level of the init
     process.

`-s'
     Ignored; for compatibility with other versions of `who'.

`-t'
`--time'
     Print last system clock change.

`-u'
     After the login time, print the number of hours and minutes that
     the user has been idle.  `.' means the user was active in the last
     minute.  `old' means the user has been idle for more than 24 hours.

`-w'
`-T'
`--mesg'
`--message'
`--writable'
     After each login name print a character indicating the user's
     message status:

          `+' allowing `write' messages
          `-' disallowing `write' messages
          `?' cannot find terminal device


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: System context,  Next: SELinux context,  Prev: User information,  Up: Top

21 System context
*****************

This section describes commands that print or change system-wide
information.

* Menu:

* date invocation::             Print or set system date and time.
* arch invocation::             Print machine hardware name.
* nproc invocation::            Print the number of processors.
* uname invocation::            Print system information.
* hostname invocation::         Print or set system name.
* hostid invocation::           Print numeric host identifier.
* uptime invocation::           Print system uptime and load.

File: coreutils.info,  Node: date invocation,  Next: arch invocation,  Up: System context

21.1 `date': Print or set system date and time
==============================================

Synopses:

     date [OPTION]... [+FORMAT]
     date [-u|--utc|--universal] [ MMDDhhmm[[CC]YY][.ss] ]

   Invoking `date' with no FORMAT argument is equivalent to invoking it
with a default format that depends on the `LC_TIME' locale category.
In the default C locale, this format is `'+%a %b %e %H:%M:%S %Z %Y'',
so the output looks like `Thu Mar  3 13:47:51 PST 2005'.

   Normally, `date' uses the time zone rules indicated by the `TZ'
environment variable, or the system default rules if `TZ' is not set.
*Note Specifying the Time Zone with `TZ': (libc)TZ Variable.

   If given an argument that starts with a `+', `date' prints the
current date and time (or the date and time specified by the `--date'
option, see below) in the format defined by that argument, which is
similar to that of the `strftime' function.  Except for conversion
specifiers, which start with `%', characters in the format string are
printed unchanged.  The conversion specifiers are described below.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

* Menu:

* Time conversion specifiers::     %[HIklMNpPrRsSTXzZ]
* Date conversion specifiers::     %[aAbBcCdDeFgGhjmuUVwWxyY]
* Literal conversion specifiers::  %[%nt]
* Padding and other flags::        Pad with zeros, spaces, etc.
* Setting the time::               Changing the system clock.
* Options for date::               Instead of the current time.
* Date input formats::             Specifying date strings.
* Examples of date::               Examples.

File: coreutils.info,  Node: Time conversion specifiers,  Next: Date conversion specifiers,  Up: date invocation

21.1.1 Time conversion specifiers
---------------------------------

`date' conversion specifiers related to times.

`%H'
     hour (`00'...`23')

`%I'
     hour (`01'...`12')

`%k'
     hour (` 0'...`23').  This is a GNU extension.

`%l'
     hour (` 1'...`12').  This is a GNU extension.

`%M'
     minute (`00'...`59')

`%N'
     nanoseconds (`000000000'...`999999999').  This is a GNU extension.

`%p'
     locale's equivalent of either `AM' or `PM'; blank in many locales.
     Noon is treated as `PM' and midnight as `AM'.

`%P'
     like `%p', except lower case.  This is a GNU extension.

`%r'
     locale's 12-hour clock time (e.g., `11:11:04 PM')

`%R'
     24-hour hour and minute.  Same as `%H:%M'.  This is a GNU
     extension.

`%s'
     seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
     Leap seconds are not counted unless leap second support is
     available.  *Note %s-examples::, for examples.  This is a GNU
     extension.

`%S'
     second (`00'...`60').  This may be `60' if leap seconds are
     supported.

`%T'
     24-hour hour, minute, and second.  Same as `%H:%M:%S'.

`%X'
     locale's time representation (e.g., `23:13:48')

`%z'
     RFC 2822/ISO 8601 style numeric time zone (e.g., `-0600' or
     `+0530'), or nothing if no time zone is determinable.  This value
     reflects the numeric time zone appropriate for the current time,
     using the time zone rules specified by the `TZ' environment
     variable.  The time (and optionally, the time zone rules) can be
     overridden by the `--date' option.  This is a GNU extension.

`%:z'
     RFC 3339/ISO 8601 style numeric time zone with `:' (e.g., `-06:00'
     or `+05:30'), or nothing if no time zone is determinable.  This is
     a GNU extension.

`%::z'
     Numeric time zone to the nearest second with `:' (e.g.,
     `-06:00:00' or `+05:30:00'), or nothing if no time zone is
     determinable.  This is a GNU extension.

`%:::z'
     Numeric time zone with `:' using the minimum necessary precision
     (e.g., `-06', `+05:30', or `-04:56:02'), or nothing if no time
     zone is determinable.  This is a GNU extension.

`%Z'
     alphabetic time zone abbreviation (e.g., `EDT'), or nothing if no
     time zone is determinable.  See `%z' for how it is determined.

File: coreutils.info,  Node: Date conversion specifiers,  Next: Literal conversion specifiers,  Prev: Time conversion specifiers,  Up: date invocation

21.1.2 Date conversion specifiers
---------------------------------

`date' conversion specifiers related to dates.

`%a'
     locale's abbreviated weekday name (e.g., `Sun')

`%A'
     locale's full weekday name, variable length (e.g., `Sunday')

`%b'
     locale's abbreviated month name (e.g., `Jan')

`%B'
     locale's full month name, variable length (e.g., `January')

`%c'
     locale's date and time (e.g., `Thu Mar  3 23:05:25 2005')

`%C'
     century.  This is like `%Y', except the last two digits are
     omitted.  For example, it is `20' if `%Y' is `2000', and is `-0'
     if `%Y' is `-001'.  It is normally at least two characters, but it
     may be more.

`%d'
     day of month (e.g., `01')

`%D'
     date; same as `%m/%d/%y'

`%e'
     day of month, space padded; same as `%_d'

`%F'
     full date in ISO 8601 format; same as `%Y-%m-%d'.  This is a good
     choice for a date format, as it is standard and is easy to sort in
     the usual case where years are in the range 0000...9999.  This is
     a GNU extension.

`%g'
     year corresponding to the ISO week number, but without the century
     (range `00' through `99').  This has the same format and value as
     `%y', except that if the ISO week number (see `%V') belongs to the
     previous or next year, that year is used instead.  This is a GNU
     extension.

`%G'
     year corresponding to the ISO week number.  This has the same
     format and value as `%Y', except that if the ISO week number (see
     `%V') belongs to the previous or next year, that year is used
     instead.  It is normally useful only if `%V' is also used; for
     example, the format `%G-%m-%d' is probably a mistake, since it
     combines the ISO week number year with the conventional month and
     day.  This is a GNU extension.

`%h'
     same as `%b'

`%j'
     day of year (`001'...`366')

`%m'
     month (`01'...`12')

`%u'
     day of week (`1'...`7') with `1' corresponding to Monday

`%U'
     week number of year, with Sunday as the first day of the week
     (`00'...`53').  Days in a new year preceding the first Sunday are
     in week zero.

`%V'
     ISO week number, that is, the week number of year, with Monday as
     the first day of the week (`01'...`53').  If the week containing
     January 1 has four or more days in the new year, then it is
     considered week 1; otherwise, it is week 53 of the previous year,
     and the next week is week 1.  (See the ISO 8601 standard.)

`%w'
     day of week (`0'...`6') with 0 corresponding to Sunday

`%W'
     week number of year, with Monday as first day of week
     (`00'...`53').  Days in a new year preceding the first Monday are
     in week zero.

`%x'
     locale's date representation (e.g., `12/31/99')

`%y'
     last two digits of year (`00'...`99')

`%Y'
     year.  This is normally at least four characters, but it may be
     more.  Year `0000' precedes year `0001', and year `-001' precedes
     year `0000'.

File: coreutils.info,  Node: Literal conversion specifiers,  Next: Padding and other flags,  Prev: Date conversion specifiers,  Up: date invocation

21.1.3 Literal conversion specifiers
------------------------------------

`date' conversion specifiers that produce literal strings.

`%%'
     a literal %

`%n'
     a newline

`%t'
     a horizontal tab

File: coreutils.info,  Node: Padding and other flags,  Next: Setting the time,  Prev: Literal conversion specifiers,  Up: date invocation

21.1.4 Padding and other flags
------------------------------

Unless otherwise specified, `date' normally pads numeric fields with
zeros, so that, for example, numeric months are always output as two
digits.  Seconds since the epoch are not padded, though, since there is
no natural width for them.

   As a GNU extension, `date' recognizes any of the following optional
flags after the `%':

`-'
     (hyphen) Do not pad the field; useful if the output is intended for
     human consumption.

`_'
     (underscore) Pad with spaces; useful if you need a fixed number of
     characters in the output, but zeros are too distracting.

`0'
     (zero) Pad with zeros even if the conversion specifier would
     normally pad with spaces.

`^'
     Use upper case characters if possible.

`#'
     Use opposite case characters if possible.  A field that is
     normally upper case becomes lower case, and vice versa.

Here are some examples of padding:

     date +%d/%m -d "Feb 1"
     => 01/02
     date +%-d/%-m -d "Feb 1"
     => 1/2
     date +%_d/%_m -d "Feb 1"
     =>  1/ 2

   As a GNU extension, you can specify the field width (after any flag,
if present) as a decimal number.  If the natural size of the output of
the field has less than the specified number of characters, the result
is written right adjusted and padded to the given size.  For example,
`%9B' prints the right adjusted month name in a field of width 9.

   An optional modifier can follow the optional flag and width
specification.  The modifiers are:

`E'
     Use the locale's alternate representation for date and time.  This
     modifier applies to the `%c', `%C', `%x', `%X', `%y' and `%Y'
     conversion specifiers.  In a Japanese locale, for example, `%Ex'
     might yield a date format based on the Japanese Emperors' reigns.

`O'
     Use the locale's alternate numeric symbols for numbers.  This
     modifier applies only to numeric conversion specifiers.

   If the format supports the modifier but no alternate representation
is available, it is ignored.

File: coreutils.info,  Node: Setting the time,  Next: Options for date,  Prev: Padding and other flags,  Up: date invocation

21.1.5 Setting the time
-----------------------

If given an argument that does not start with `+', `date' sets the
system clock to the date and time specified by that argument (as
described below).  You must have appropriate privileges to set the
system clock.  The `--date' and `--set' options may not be used with
such an argument.  The `--universal' option may be used with such an
argument to indicate that the specified date and time are relative to
Coordinated Universal Time rather than to the local time zone.

   The argument must consist entirely of digits, which have the
following meaning:

`MM'
     month

`DD'
     day within month

`hh'
     hour

`mm'
     minute

`CC'
     first two digits of year (optional)

`YY'
     last two digits of year (optional)

`ss'
     second (optional)

   The `--set' option also sets the system clock; see the next section.

File: coreutils.info,  Node: Options for date,  Prev: Setting the time,  Up: date invocation

21.1.6 Options for `date'
-------------------------

The program accepts the following options.  Also see *note Common
options::.

`-d DATESTR'
`--date=DATESTR'
     Display the date and time specified in DATESTR instead of the
     current date and time.  DATESTR can be in almost any common
     format.  It can contain month names, time zones, `am' and `pm',
     `yesterday', etc.  For example, `--date="2004-02-27
     14:19:13.489392193 +0530"' specifies the instant of time that is
     489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
     time zone that is 5 hours and 30 minutes east of UTC.
     Note: input currently must be in locale independent format. E.g.,
     the LC_TIME=C below is needed to print back the correct date in
     many locales:
          date -d "$(LC_TIME=C date)"
     *Note Date input formats::.

`-f DATEFILE'
`--file=DATEFILE'
     Parse each line in DATEFILE as with `-d' and display the resulting
     date and time.  If DATEFILE is `-', use standard input.  This is
     useful when you have many dates to process, because the system
     overhead of starting up the `date' executable many times can be
     considerable.

`-r FILE'
`--reference=FILE'
     Display the date and time of the last modification of FILE,
     instead of the current date and time.

`-R'
`--rfc-822'
`--rfc-2822'
     Display the date and time using the format `%a, %d %b %Y %H:%M:%S
     %z', evaluated in the C locale so abbreviations are always in
     English.  For example:

          Fri, 09 Sep 2005 13:51:39 -0700

     This format conforms to Internet RFCs 2822
     (ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt) and 822
     (ftp://ftp.rfc-editor.org/in-notes/rfc822.txt), the current and
     previous standards for Internet email.

`--rfc-3339=TIMESPEC'
     Display the date using a format specified by Internet RFC 3339
     (ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt).  This is a subset
     of the ISO 8601 format, except that it also permits applications
     to use a space rather than a `T' to separate dates from times.
     Unlike the other standard formats, RFC 3339 format is always
     suitable as input for the `--date' (`-d') and `--file' (`-f')
     options, regardless of the current locale.

     The argument TIMESPEC specifies how much of the time to include.
     It can be one of the following:

    `date'
          Print just the full-date, e.g., `2005-09-14'.  This is
          equivalent to the format `%Y-%m-%d'.

    `seconds'
          Print the full-date and full-time separated by a space, e.g.,
          `2005-09-14 00:56:06+05:30'.  The output ends with a numeric
          time-offset; here the `+05:30' means that local time is five
          hours and thirty minutes east of UTC.  This is equivalent to
          the format `%Y-%m-%d %H:%M:%S%:z'.

    `ns'
          Like `seconds', but also print nanoseconds, e.g., `2005-09-14
          00:56:06.998458565+05:30'.  This is equivalent to the format
          `%Y-%m-%d %H:%M:%S.%N%:z'.


`-s DATESTR'
`--set=DATESTR'
     Set the date and time to DATESTR.  See `-d' above.

`-u'
`--utc'
`--universal'
     Use Coordinated Universal Time (UTC) by operating as if the `TZ'
     environment variable were set to the string `UTC0'.  Coordinated
     Universal Time is often called "Greenwich Mean Time" (GMT) for
     historical reasons.

File: coreutils.info,  Node: Date input formats,  Next: Opening the software toolbox,  Prev: File permissions,  Up: Top

28 Date input formats
*********************

First, a quote:

     Our units of temporal measurement, from seconds on up to months,
     are so complicated, asymmetrical and disjunctive so as to make
     coherent mental reckoning in time all but impossible.  Indeed, had
     some tyrannical god contrived to enslave our minds to time, to
     make it all but impossible for us to escape subjection to sodden
     routines and unpleasant surprises, he could hardly have done
     better than handing down our present system.  It is like a set of
     trapezoidal building blocks, with no vertical or horizontal
     surfaces, like a language in which the simplest thought demands
     ornate constructions, useless particles and lengthy
     circumlocutions.  Unlike the more successful patterns of language
     and science, which enable us to face experience boldly or at least
     level-headedly, our system of temporal calculation silently and
     persistently encourages our terror of time.

     ...  It is as though architects had to measure length in feet,
     width in meters and height in ells; as though basic instruction
     manuals demanded a knowledge of five different languages.  It is
     no wonder then that we often look into our own immediate past or
     future, last Tuesday or a week from Sunday, with feelings of
     helpless confusion.  ...

     -- Robert Grudin, `Time and the Art of Living'.

   This section describes the textual date representations that GNU
programs accept.  These are the strings you, as a user, can supply as
arguments to the various programs.  The C interface (via the `get_date'
function) is not described here.

* Menu:

* General date syntax::            Common rules.
* Calendar date items::            19 Dec 1994.
* Time of day items::              9:20pm.
* Time zone items::                EST, PDT, GMT.
* Day of week items::              Monday and others.
* Relative items in date strings:: next tuesday, 2 years ago.
* Pure numbers in date strings::   19931219, 1440.
* Seconds since the Epoch::        @1078100502.
* Specifying time zone rules::     TZ="America/New_York", TZ="UTC0".
* Authors of get_date::            Bellovin, Eggert, Salz, Berets, et al.

File: coreutils.info,  Node: General date syntax,  Next: Calendar date items,  Up: Date input formats

28.1 General date syntax
========================

A "date" is a string, possibly empty, containing many items separated
by whitespace.  The whitespace may be omitted when no ambiguity arises.
The empty string means the beginning of today (i.e., midnight).  Order
of the items is immaterial.  A date string may contain many flavors of
items:

   * calendar date items

   * time of day items

   * time zone items

   * day of the week items

   * relative items

   * pure numbers.

We describe each of these item types in turn, below.

   A few ordinal numbers may be written out in words in some contexts.
This is most useful for specifying day of the week items or relative
items (see below).  Among the most commonly used ordinal numbers, the
word `last' stands for -1, `this' stands for 0, and `first' and `next'
both stand for 1.  Because the word `second' stands for the unit of
time there is no way to write the ordinal number 2, but for convenience
`third' stands for 3, `fourth' for 4, `fifth' for 5, `sixth' for 6,
`seventh' for 7, `eighth' for 8, `ninth' for 9, `tenth' for 10,
`eleventh' for 11 and `twelfth' for 12.

   When a month is written this way, it is still considered to be
written numerically, instead of being "spelled in full"; this changes
the allowed strings.

   In the current implementation, only English is supported for words
and abbreviations like `AM', `DST', `EST', `first', `January',
`Sunday', `tomorrow', and `year'.

   The output of the `date' command is not always acceptable as a date
string, not only because of the language problem, but also because
there is no standard meaning for time zone items like `IST'.  When using
`date' to generate a date string intended to be parsed later, specify a
date format that is independent of language and that does not use time
zone items other than `UTC' and `Z'.  Here are some ways to do this:

     $ LC_ALL=C TZ=UTC0 date
     Mon Mar  1 00:21:42 UTC 2004
     $ TZ=UTC0 date +'%Y-%m-%d %H:%M:%SZ'
     2004-03-01 00:21:42Z
     $ date --iso-8601=ns | tr T ' '  # --iso-8601 is a GNU extension.
     2004-02-29 16:21:42,692722128-0800
     $ date --rfc-2822  # a GNU extension
     Sun, 29 Feb 2004 16:21:42 -0800
     $ date +'%Y-%m-%d %H:%M:%S %z'  # %z is a GNU extension.
     2004-02-29 16:21:42 -0800
     $ date +'@%s.%N'  # %s and %N are GNU extensions.
     @1078100502.692722128

   Alphabetic case is completely ignored in dates.  Comments may be
introduced between round parentheses, as long as included parentheses
are properly nested.  Hyphens not followed by a digit are currently
ignored.  Leading zeros on numbers are ignored.

   Invalid dates like `2005-02-29' or times like `24:00' are rejected.
In the typical case of a host that does not support leap seconds, a
time like `23:59:60' is rejected even if it corresponds to a valid leap
second.

File: coreutils.info,  Node: Calendar date items,  Next: Time of day items,  Prev: General date syntax,  Up: Date input formats

28.2 Calendar date items
========================

A "calendar date item" specifies a day of the year.  It is specified
differently, depending on whether the month is specified numerically or
literally.  All these strings specify the same calendar date:

     1972-09-24     # ISO 8601.
     72-9-24        # Assume 19xx for 69 through 99,
                    # 20xx for 00 through 68.
     72-09-24       # Leading zeros are ignored.
     9/24/72        # Common U.S. writing.
     24 September 1972
     24 Sept 72     # September has a special abbreviation.
     24 Sep 72      # Three-letter abbreviations always allowed.
     Sep 24, 1972
     24-sep-72
     24sep72

   The year can also be omitted.  In this case, the last specified year
is used, or the current year if none.  For example:

     9/24
     sep 24

   Here are the rules.

   For numeric months, the ISO 8601 format `YEAR-MONTH-DAY' is allowed,
where YEAR is any positive number, MONTH is a number between 01 and 12,
and DAY is a number between 01 and 31.  A leading zero must be present
if a number is less than ten.  If YEAR is 68 or smaller, then 2000 is
added to it; otherwise, if YEAR is less than 100, then 1900 is added to
it.  The construct `MONTH/DAY/YEAR', popular in the United States, is
accepted.  Also `MONTH/DAY', omitting the year.

   Literal months may be spelled out in full: `January', `February',
`March', `April', `May', `June', `July', `August', `September',
`October', `November' or `December'.  Literal months may be abbreviated
to their first three letters, possibly followed by an abbreviating dot.
It is also permitted to write `Sept' instead of `September'.

   When months are written literally, the calendar date may be given as
any of the following:

     DAY MONTH YEAR
     DAY MONTH
     MONTH DAY YEAR
     DAY-MONTH-YEAR

   Or, omitting the year:

     MONTH DAY

File: coreutils.info,  Node: Time of day items,  Next: Time zone items,  Prev: Calendar date items,  Up: Date input formats

28.3 Time of day items
======================

A "time of day item" in date strings specifies the time on a given day.
Here are some examples, all of which represent the same time:

     20:02:00.000000
     20:02
     8:02pm
     20:02-0500      # In EST (U.S. Eastern Standard Time).

   More generally, the time of day may be given as
`HOUR:MINUTE:SECOND', where HOUR is a number between 0 and 23, MINUTE
is a number between 0 and 59, and SECOND is a number between 0 and 59
possibly followed by `.' or `,' and a fraction containing one or more
digits.  Alternatively, `:SECOND' can be omitted, in which case it is
taken to be zero.  On the rare hosts that support leap seconds, SECOND
may be 60.

   If the time is followed by `am' or `pm' (or `a.m.' or `p.m.'), HOUR
is restricted to run from 1 to 12, and `:MINUTE' may be omitted (taken
to be zero).  `am' indicates the first half of the day, `pm' indicates
the second half of the day.  In this notation, 12 is the predecessor of
1: midnight is `12am' while noon is `12pm'.  (This is the zero-oriented
interpretation of `12am' and `12pm', as opposed to the old tradition
derived from Latin which uses `12m' for noon and `12pm' for midnight.)

   The time may alternatively be followed by a time zone correction,
expressed as `SHHMM', where S is `+' or `-', HH is a number of zone
hours and MM is a number of zone minutes.  The zone minutes term, MM,
may be omitted, in which case the one- or two-digit correction is
interpreted as a number of hours.  You can also separate HH from MM
with a colon.  When a time zone correction is given this way, it forces
interpretation of the time relative to Coordinated Universal Time
(UTC), overriding any previous specification for the time zone or the
local time zone.  For example, `+0530' and `+05:30' both stand for the
time zone 5.5 hours ahead of UTC (e.g., India).  This is the best way to
specify a time zone correction by fractional parts of an hour.  The
maximum zone correction is 24 hours.

   Either `am'/`pm' or a time zone correction may be specified, but not
both.

File: coreutils.info,  Node: Time zone items,  Next: Day of week items,  Prev: Time of day items,  Up: Date input formats

28.4 Time zone items
====================

A "time zone item" specifies an international time zone, indicated by a
small set of letters, e.g., `UTC' or `Z' for Coordinated Universal
Time.  Any included periods are ignored.  By following a
non-daylight-saving time zone by the string `DST' in a separate word
(that is, separated by some white space), the corresponding daylight
saving time zone may be specified.  Alternatively, a
non-daylight-saving time zone can be followed by a time zone
correction, to add the two values.  This is normally done only for
`UTC'; for example, `UTC+05:30' is equivalent to `+05:30'.

   Time zone items other than `UTC' and `Z' are obsolescent and are not
recommended, because they are ambiguous; for example, `EST' has a
different meaning in Australia than in the United States.  Instead,
it's better to use unambiguous numeric time zone corrections like
`-0500', as described in the previous section.

   If neither a time zone item nor a time zone correction is supplied,
time stamps are interpreted using the rules of the default time zone
(*note Specifying time zone rules::).

File: coreutils.info,  Node: Day of week items,  Next: Relative items in date strings,  Prev: Time zone items,  Up: Date input formats

28.5 Day of week items
======================

The explicit mention of a day of the week will forward the date (only
if necessary) to reach that day of the week in the future.

   Days of the week may be spelled out in full: `Sunday', `Monday',
`Tuesday', `Wednesday', `Thursday', `Friday' or `Saturday'.  Days may
be abbreviated to their first three letters, optionally followed by a
period.  The special abbreviations `Tues' for `Tuesday', `Wednes' for
`Wednesday' and `Thur' or `Thurs' for `Thursday' are also allowed.

   A number may precede a day of the week item to move forward
supplementary weeks.  It is best used in expression like `third
monday'.  In this context, `last DAY' or `next DAY' is also acceptable;
they move one week before or after the day that DAY by itself would
represent.

   A comma following a day of the week item is ignored.

File: coreutils.info,  Node: Relative items in date strings,  Next: Pure numbers in date strings,  Prev: Day of week items,  Up: Date input formats

28.6 Relative items in date strings
===================================

"Relative items" adjust a date (or the current date if none) forward or
backward.  The effects of relative items accumulate.  Here are some
examples:

     1 year
     1 year ago
     3 years
     2 days

   The unit of time displacement may be selected by the string `year'
or `month' for moving by whole years or months.  These are fuzzy units,
as years and months are not all of equal duration.  More precise units
are `fortnight' which is worth 14 days, `week' worth 7 days, `day'
worth 24 hours, `hour' worth 60 minutes, `minute' or `min' worth 60
seconds, and `second' or `sec' worth one second.  An `s' suffix on
these units is accepted and ignored.

   The unit of time may be preceded by a multiplier, given as an
optionally signed number.  Unsigned numbers are taken as positively
signed.  No number at all implies 1 for a multiplier.  Following a
relative item by the string `ago' is equivalent to preceding the unit
by a multiplier with value -1.

   The string `tomorrow' is worth one day in the future (equivalent to
`day'), the string `yesterday' is worth one day in the past (equivalent
to `day ago').

   The strings `now' or `today' are relative items corresponding to
zero-valued time displacement, these strings come from the fact a
zero-valued time displacement represents the current time when not
otherwise changed by previous items.  They may be used to stress other
items, like in `12:00 today'.  The string `this' also has the meaning
of a zero-valued time displacement, but is preferred in date strings
like `this thursday'.

   When a relative item causes the resulting date to cross a boundary
where the clocks were adjusted, typically for daylight saving time, the
resulting date and time are adjusted accordingly.

   The fuzz in units can cause problems with relative items.  For
example, `2003-07-31 -1 month' might evaluate to 2003-07-01, because
2003-06-31 is an invalid date.  To determine the previous month more
reliably, you can ask for the month before the 15th of the current
month.  For example:

     $ date -R
     Thu, 31 Jul 2003 13:02:39 -0700
     $ date --date='-1 month' +'Last month was %B?'
     Last month was July?
     $ date --date="$(date +%Y-%m-15) -1 month" +'Last month was %B!'
     Last month was June!

   Also, take care when manipulating dates around clock changes such as
daylight saving leaps.  In a few cases these have added or subtracted
as much as 24 hours from the clock, so it is often wise to adopt
universal time by setting the `TZ' environment variable to `UTC0'
before embarking on calendrical calculations.

File: coreutils.info,  Node: Pure numbers in date strings,  Next: Seconds since the Epoch,  Prev: Relative items in date strings,  Up: Date input formats

28.7 Pure numbers in date strings
=================================

The precise interpretation of a pure decimal number depends on the
context in the date string.

   If the decimal number is of the form YYYYMMDD and no other calendar
date item (*note Calendar date items::) appears before it in the date
string, then YYYY is read as the year, MM as the month number and DD as
the day of the month, for the specified calendar date.

   If the decimal number is of the form HHMM and no other time of day
item appears before it in the date string, then HH is read as the hour
of the day and MM as the minute of the hour, for the specified time of
day.  MM can also be omitted.

   If both a calendar date and a time of day appear to the left of a
number in the date string, but no relative item, then the number
overrides the year.

File: coreutils.info,  Node: Seconds since the Epoch,  Next: Specifying time zone rules,  Prev: Pure numbers in date strings,  Up: Date input formats

28.8 Seconds since the Epoch
============================

If you precede a number with `@', it represents an internal time stamp
as a count of seconds.  The number can contain an internal decimal
point (either `.' or `,'); any excess precision not supported by the
internal representation is truncated toward minus infinity.  Such a
number cannot be combined with any other date item, as it specifies a
complete time stamp.

   Internally, computer times are represented as a count of seconds
since an epoch--a well-defined point of time.  On GNU and POSIX
systems, the epoch is 1970-01-01 00:00:00 UTC, so `@0' represents this
time, `@1' represents 1970-01-01 00:00:01 UTC, and so forth.  GNU and
most other POSIX-compliant systems support such times as an extension
to POSIX, using negative counts, so that `@-1' represents 1969-12-31
23:59:59 UTC.

   Traditional Unix systems count seconds with 32-bit two's-complement
integers and can represent times from 1901-12-13 20:45:52 through
2038-01-19 03:14:07 UTC.  More modern systems use 64-bit counts of
seconds with nanosecond subcounts, and can represent all the times in
the known lifetime of the universe to a resolution of 1 nanosecond.

   On most hosts, these counts ignore the presence of leap seconds.
For example, on most hosts `@915148799' represents 1998-12-31 23:59:59
UTC, `@915148800' represents 1999-01-01 00:00:00 UTC, and there is no
way to represent the intervening leap second 1998-12-31 23:59:60 UTC.

File: coreutils.info,  Node: Specifying time zone rules,  Next: Authors of get_date,  Prev: Seconds since the Epoch,  Up: Date input formats

28.9 Specifying time zone rules
===============================

Normally, dates are interpreted using the rules of the current time
zone, which in turn are specified by the `TZ' environment variable, or
by a system default if `TZ' is not set.  To specify a different set of
default time zone rules that apply just to one date, start the date
with a string of the form `TZ="RULE"'.  The two quote characters (`"')
must be present in the date, and any quotes or backslashes within RULE
must be escaped by a backslash.

   For example, with the GNU `date' command you can answer the question
"What time is it in New York when a Paris clock shows 6:30am on October
31, 2004?" by using a date beginning with `TZ="Europe/Paris"' as shown
in the following shell transcript:

     $ export TZ="America/New_York"
     $ date --date='TZ="Europe/Paris" 2004-10-31 06:30'
     Sun Oct 31 01:30:00 EDT 2004

   In this example, the `--date' operand begins with its own `TZ'
setting, so the rest of that operand is processed according to
`Europe/Paris' rules, treating the string `2004-10-31 06:30' as if it
were in Paris.  However, since the output of the `date' command is
processed according to the overall time zone rules, it uses New York
time.  (Paris was normally six hours ahead of New York in 2004, but
this example refers to a brief Halloween period when the gap was five
hours.)

   A `TZ' value is a rule that typically names a location in the `tz'
database (http://www.twinsun.com/tz/tz-link.htm).  A recent catalog of
location names appears in the TWiki Date and Time Gateway
(http://twiki.org/cgi-bin/xtra/tzdate).  A few non-GNU hosts require a
colon before a location name in a `TZ' setting, e.g.,
`TZ=":America/New_York"'.

   The `tz' database includes a wide variety of locations ranging from
`Arctic/Longyearbyen' to `Antarctica/South_Pole', but if you are at sea
and have your own private time zone, or if you are using a non-GNU host
that does not support the `tz' database, you may need to use a POSIX
rule instead.  Simple POSIX rules like `UTC0' specify a time zone
without daylight saving time; other rules can specify simple daylight
saving regimes.  *Note Specifying the Time Zone with `TZ': (libc)TZ
Variable.

File: coreutils.info,  Node: Authors of get_date,  Prev: Specifying time zone rules,  Up: Date input formats

28.10 Authors of `get_date'
===========================

`get_date' was originally implemented by Steven M. Bellovin
(<smb AT research.com>) while at the University of North Carolina at
Chapel Hill.  The code was later tweaked by a couple of people on
Usenet, then completely overhauled by Rich $alz (<rsalz AT bbn.com>) and
Jim Berets (<jberets AT bbn.com>) in August, 1990.  Various revisions for
the GNU system were made by David MacKenzie, Jim Meyering, Paul Eggert
and others.

   This chapter was originally produced by Franc,ois Pinard
(<pinard AT iro.ca>) from the `getdate.y' source code, and then
edited by K. Berry (<kb AT cs.edu>).

File: coreutils.info,  Node: Examples of date,  Up: date invocation

21.1.7 Examples of `date'
-------------------------

Here are a few examples.  Also see the documentation for the `-d'
option in the previous section.

   * To print the date of the day before yesterday:

          date --date='2 days ago'

   * To print the date of the day three months and one day hence:

          date --date='3 months 1 day'

   * To print the day of year of Christmas in the current year:

          date --date='25 Dec' +%j

   * To print the current full month name and the day of the month:

          date '+%B %d'

     But this may not be what you want because for the first nine days
     of the month, the `%d' expands to a zero-padded two-digit field,
     for example `date -d 1may '+%B %d'' will print `May 01'.

   * To print a date without the leading zero for one-digit days of the
     month, you can use the (GNU extension) `-' flag to suppress the
     padding altogether:

          date -d 1may '+%B %-d

   * To print the current date and time in the format required by many
     non-GNU versions of `date' when setting the system clock:

          date +%m%d%H%M%Y.%S

   * To set the system clock forward by two minutes:

          date --set='+2 minutes'

   * To print the date in RFC 2822 format, use `date --rfc-2822'.  Here
     is some example output:

          Fri, 09 Sep 2005 13:51:39 -0700

   * To convert a date string to the number of seconds since the epoch
     (which is 1970-01-01 00:00:00 UTC), use the `--date' option with
     the `%s' format.  That can be useful in sorting and/or graphing
     and/or comparing data by date.  The following command outputs the
     number of the seconds since the epoch for the time two minutes
     after the epoch:

          date --date='1970-01-01 00:02:00 +0000' +%s
          120

     If you do not specify time zone information in the date string,
     `date' uses your computer's idea of the time zone when
     interpreting the string.  For example, if your computer's time
     zone is that of Cambridge, Massachusetts, which was then 5 hours
     (i.e., 18,000 seconds) behind UTC:

          # local time zone used
          date --date='1970-01-01 00:02:00' +%s
          18120

   * If you're sorting or graphing dated data, your raw date values may
     be represented as seconds since the epoch.  But few people can
     look at the date `946684800' and casually note "Oh, that's the
     first second of the year 2000 in Greenwich, England."

          date --date='2000-01-01 UTC' +%s
          946684800

     An alternative is to use the `--utc' (`-u') option.  Then you may
     omit `UTC' from the date string.  Although this produces the same
     result for `%s' and many other format sequences, with a time zone
     offset different from zero, it would give a different result for
     zone-dependent formats like `%z'.

          date -u --date=2000-01-01 +%s
          946684800

     To convert such an unwieldy number of seconds back to a more
     readable form, use a command like this:

          # local time zone used
          date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
          1999-12-31 19:00:00 -0500

     Or if you do not mind depending on the `@' feature present since
     coreutils 5.3.0, you could shorten this to:

          date -d @946684800 +"%F %T %z"
          1999-12-31 19:00:00 -0500

     Often it is better to output UTC-relative date and time:

          date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
          2000-01-01 00:00:00 +0000


File: coreutils.info,  Node: arch invocation,  Next: nproc invocation,  Prev: date invocation,  Up: System context

21.2 `arch': Print machine hardware name
========================================

`arch' prints the machine hardware name, and is equivalent to `uname
-m'.  Synopsis:

     arch [OPTION]

   The program accepts the *note Common options:: only.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: nproc invocation,  Next: uname invocation,  Prev: arch invocation,  Up: System context

21.3 `nproc': Print the number of available processors
======================================================

Print the number of processing units available to the current process,
which may be less than the number of online processors.  If this
information is not accessible, then print the number of processors
installed.  If the `OMP_NUM_THREADS' environment variable is set, then
it will determine the returned value.  The result is guaranteed to be
greater than zero.  Synopsis:

     nproc [OPTION]

   The program accepts the following options.  Also see *note Common
options::.

`--all'
     Print the number of installed processors on the system, which may
     be greater than the number online or available to the current
     process.  The `OMP_NUM_THREADS' environment variable is not
     honored in this case.

`--ignore=NUMBER'
     If possible, exclude this NUMBER of processing units.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: uname invocation,  Next: hostname invocation,  Prev: nproc invocation,  Up: System context

21.4 `uname': Print system information
======================================

`uname' prints information about the machine and operating system it is
run on.  If no options are given, `uname' acts as if the `-s' option
were given.  Synopsis:

     uname [OPTION]...

   If multiple options or `-a' are given, the selected information is
printed in this order:

     KERNEL-NAME NODENAME KERNEL-RELEASE KERNEL-VERSION
     MACHINE PROCESSOR HARDWARE-PLATFORM OPERATING-SYSTEM

   The information may contain internal spaces, so such output cannot be
parsed reliably.  In the following example, RELEASE is
`2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001':

     uname -a
     => Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux

   The program accepts the following options.  Also see *note Common
options::.

`-a'
`--all'
     Print all of the below information, except omit the processor type
     and the hardware platform name if they are unknown.

`-i'
`--hardware-platform'
     Print the hardware platform name (sometimes called the hardware
     implementation).  Print `unknown' if the kernel does not make this
     information easily available, as is the case with Linux kernels.

`-m'
`--machine'
     Print the machine hardware name (sometimes called the hardware
     class or hardware type).

`-n'
`--nodename'
     Print the network node hostname.

`-p'
`--processor'
     Print the processor type (sometimes called the instruction set
     architecture or ISA).  Print `unknown' if the kernel does not make
     this information easily available, as is the case with Linux
     kernels.

`-o'
`--operating-system'
     Print the name of the operating system.

`-r'
`--kernel-release'
     Print the kernel release.

`-s'
`--kernel-name'
     Print the kernel name.  POSIX 1003.1-2001 (*note Standards
     conformance::) calls this "the implementation of the operating
     system", because the POSIX specification itself has no notion of
     "kernel".  The kernel name might be the same as the operating
     system name printed by the `-o' or `--operating-system' option,
     but it might differ.  Some operating systems (e.g., FreeBSD,
     HP-UX) have the same name as their underlying kernels; others
     (e.g., GNU/Linux, Solaris) do not.

`-v'
`--kernel-version'
     Print the kernel version.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: hostname invocation,  Next: hostid invocation,  Prev: uname invocation,  Up: System context

21.5 `hostname': Print or set system name
=========================================

With no arguments, `hostname' prints the name of the current host
system.  With one argument, it sets the current host name to the
specified string.  You must have appropriate privileges to set the host
name.  Synopsis:

     hostname [NAME]

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: hostid invocation,  Next: uptime invocation,  Prev: hostname invocation,  Up: System context

21.6 `hostid': Print numeric host identifier
============================================

`hostid' prints the numeric identifier of the current host in
hexadecimal.  This command accepts no arguments.  The only options are
`--help' and `--version'.  *Note Common options::.

   For example, here's what it prints on one system I use:

     $ hostid
     1bac013d

   On that system, the 32-bit quantity happens to be closely related to
the system's Internet address, but that isn't always the case.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: uptime invocation,  Prev: hostid invocation,  Up: System context

21.7 `uptime': Print system uptime and load
===========================================

`uptime' prints the current time, the system's uptime, the number of
logged-in users and the current load average.

   If an argument is specified, it is used as the file to be read to
discover how many users are logged in.  If no argument is specified, a
system default is used (`uptime --help' indicates the default setting).

   The only options are `--help' and `--version'.  *Note Common
options::.

   For example, here's what it prints right now on one system I use:

     $ uptime
      14:07  up   3:35,  3 users,  load average: 1.39, 1.15, 1.04

   The precise method of calculation of load average varies somewhat
between systems.  Some systems calculate it as the average number of
runnable processes over the last 1, 5 and 15 minutes, but some systems
also include processes in the uninterruptible sleep state (that is,
those processes which are waiting for disk I/O).  The Linux kernel
includes uninterruptible processes.

File: coreutils.info,  Node: SELinux context,  Next: Modified command invocation,  Prev: System context,  Up: Top

22 SELinux context
******************

This section describes commands for operations with SELinux contexts.

* Menu:

* chcon invocation::            Change SELinux context of file
* runcon invocation::           Run a command in specified SELinux context

File: coreutils.info,  Node: chcon invocation,  Next: runcon invocation,  Up: SELinux context

22.1 `chcon': Change SELinux context of file
============================================

`chcon' changes the SELinux security context of the selected files.
Synopses:

     chcon [OPTION]... CONTEXT FILE...
     chcon [OPTION]... [-u USER] [-r ROLE] [-l RANGE] [-t TYPE] FILE...
     chcon [OPTION]... --reference=RFILE FILE...

   Change the SELinux security context of each FILE to CONTEXT.  With
`--reference', change the security context of each FILE to that of
RFILE.

   The program accepts the following options.  Also see *note Common
options::.

`-h'
`--no-dereference'
     Affect symbolic links instead of any referenced file.

`--reference=RFILE'
     Use RFILE's security context rather than specifying a CONTEXT
     value.

`-R'
`--recursive'
     Operate on files and directories recursively.

`-H'
     If `--recursive' (`-R') is specified and a command line argument
     is a symbolic link to a directory, traverse it.  *Note Traversing
     symlinks::.

`-L'
     In a recursive traversal, traverse every symbolic link to a
     directory that is encountered.  *Note Traversing symlinks::.

`-P'
     Do not traverse any symbolic links.  This is the default if none
     of `-H', `-L', or `-P' is specified.  *Note Traversing symlinks::.

`-v'
`--verbose'
     Output a diagnostic for every file processed.

`-u USER'
`--user=USER'
     Set user USER in the target security context.

`-r ROLE'
`--role=ROLE'
     Set role ROLE in the target security context.

`-t TYPE'
`--type=TYPE'
     Set type TYPE in the target security context.

`-l RANGE'
`--range=RANGE'
     Set range RANGE in the target security context.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: runcon invocation,  Prev: chcon invocation,  Up: SELinux context

22.2 `runcon': Run a command in specified SELinux context
=========================================================

`runcon' runs file in specified SELinux security context.

   Synopses:
     runcon CONTEXT COMMAND [ARGS]
     runcon [ -c ] [-u USER] [-r ROLE] [-t TYPE] [-l RANGE] COMMAND [ARGS]

   Run COMMAND with completely-specified CONTEXT, or with current or
transitioned security context modified by one or more of LEVEL, ROLE,
TYPE and USER.

   If none of `-c', `-t', `-u', `-r', or `-l' is specified, the first
argument is used as the complete context.  Any additional arguments
after COMMAND are interpreted as arguments to the command.

   With neither CONTEXT nor COMMAND, print the current security context.

   The program accepts the following options.  Also see *note Common
options::.

`-c'
`--compute'
     Compute process transition context before modifying.

`-u USER'
`--user=USER'
     Set user USER in the target security context.

`-r ROLE'
`--role=ROLE'
     Set role ROLE in the target security context.

`-t TYPE'
`--type=TYPE'
     Set type TYPE in the target security context.

`-l RANGE'
`--range=RANGE'
     Set range RANGE in the target security context.


   Exit status:

     126 if COMMAND is found but cannot be invoked
     127 if `runcon' itself fails or if COMMAND cannot be found
     the exit status of COMMAND otherwise

File: coreutils.info,  Node: Modified command invocation,  Next: Process control,  Prev: SELinux context,  Up: Top

23 Modified command invocation
******************************

This section describes commands that run other commands in some context
different than the current one: a modified environment, as a different
user, etc.

* Menu:

* chroot invocation::           Modify the root directory.
* env invocation::              Modify environment variables.
* nice invocation::             Modify niceness.
* nohup invocation::            Immunize to hangups.
* stdbuf invocation::           Modify buffering of standard streams.
* su invocation::               Modify user and group ID.
* timeout invocation::          Run with time limit.

File: coreutils.info,  Node: chroot invocation,  Next: env invocation,  Up: Modified command invocation

23.1 `chroot': Run a command with a different root directory
============================================================

`chroot' runs a command with a specified root directory.  On many
systems, only the super-user can do this.(1) Synopses:

     chroot OPTION NEWROOT [COMMAND [ARGS]...]
     chroot OPTION

   Ordinarily, file names are looked up starting at the root of the
directory structure, i.e., `/'.  `chroot' changes the root to the
directory NEWROOT (which must exist) and then runs COMMAND with
optional ARGS.  If COMMAND is not specified, the default is the value
of the `SHELL' environment variable or `/bin/sh' if not set, invoked
with the `-i' option.  COMMAND must not be a special built-in utility
(*note Special built-in utilities::).

   The program accepts the following options.  Also see *note Common
options::.  Options must precede operands.

`--userspec=USER[:GROUP]'
     By default, COMMAND is run with the same credentials as the
     invoking process.  Use this option to run it as a different USER
     and/or with a different primary GROUP.

`--groups=GROUPS'
     Use this option to specify the supplementary GROUPS to be used by
     the new process.  The items in the list (names or numeric IDs)
     must be separated by commas.


   Here are a few tips to help avoid common problems in using chroot.
To start with a simple example, make COMMAND refer to a statically
linked binary.  If you were to use a dynamically linked executable, then
you'd have to arrange to have the shared libraries in the right place
under your new root directory.

   For example, if you create a statically linked `ls' executable, and
put it in `/tmp/empty', you can run this command as root:

     $ chroot /tmp/empty /ls -Rl /

   Then you'll see output like this:

     /:
     total 1023
     -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls

   If you want to use a dynamically linked executable, say `bash', then
first run `ldd bash' to see what shared objects it needs.  Then, in
addition to copying the actual binary, also copy the listed files to
the required positions under your intended new root directory.
Finally, if the executable requires any other files (e.g., data, state,
device files), copy them into place, too.

   Exit status:

     125 if `chroot' itself fails
     126 if COMMAND is found but cannot be invoked
     127 if COMMAND cannot be found
     the exit status of COMMAND otherwise

   ---------- Footnotes ----------

   (1) However, some systems (e.g., FreeBSD) can be configured to allow
certain regular users to use the `chroot' system call, and hence to run
this program.  Also, on Cygwin, anyone can run the `chroot' command,
because the underlying function is non-privileged due to lack of
support in MS-Windows.

File: coreutils.info,  Node: env invocation,  Next: nice invocation,  Prev: chroot invocation,  Up: Modified command invocation

23.2 `env': Run a command in a modified environment
===================================================

`env' runs a command with a modified environment.  Synopses:

     env [OPTION]... [NAME=VALUE]... [COMMAND [ARGS]...]
     env

   Operands of the form `VARIABLE=VALUE' set the environment variable
VARIABLE to value VALUE.  VALUE may be empty (`VARIABLE=').  Setting a
variable to an empty value is different from unsetting it.  These
operands are evaluated left-to-right, so if two operands mention the
same variable the earlier is ignored.

   Environment variable names can be empty, and can contain any
characters other than `=' and ASCII NUL.  However, it is wise to limit
yourself to names that consist solely of underscores, digits, and ASCII
letters, and that begin with a non-digit, as applications like the
shell do not work well with other names.

   The first operand that does not contain the character `=' specifies
the program to invoke; it is searched for according to the `PATH'
environment variable.  Any remaining arguments are passed as arguments
to that program.  The program should not be a special built-in utility
(*note Special built-in utilities::).

   Modifications to `PATH' take effect prior to searching for COMMAND.
Use caution when reducing `PATH'; behavior is not portable when `PATH'
is undefined or omits key directories such as `/bin'.

   In the rare case that a utility contains a `=' in the name, the only
way to disambiguate it from a variable assignment is to use an
intermediate command for COMMAND, and pass the problematic program name
via ARGS.  For example, if `./prog=' is an executable in the current
`PATH':

     env prog= true # runs 'true', with prog= in environment
     env ./prog= true # runs 'true', with ./prog= in environment
     env -- prog= true # runs 'true', with prog= in environment
     env sh -c '\prog= true' # runs 'prog=' with argument 'true'
     env sh -c 'exec "$@"' sh prog= true # also runs 'prog='

   If no command name is specified following the environment
specifications, the resulting environment is printed.  This is like
specifying the `printenv' program.

   For some examples, suppose the environment passed to `env' contains
`LOGNAME=rms', `EDITOR=emacs', and `PATH=.:/gnubin:/hacks':

   * Output the current environment.
          $ env | LC_ALL=C sort
          EDITOR=emacs
          LOGNAME=rms
          PATH=.:/gnubin:/hacks

   * Run `foo' with a reduced environment, preserving only the original
     `PATH' to avoid problems in locating `foo'.
          env - PATH="$PATH" foo

   * Run `foo' with the environment containing `LOGNAME=rms',
     `EDITOR=emacs', and `PATH=.:/gnubin:/hacks', and guarantees that
     `foo' was found in the file system rather than as a shell built-in.
          env foo

   * Run `nemacs' with the environment containing `LOGNAME=foo',
     `EDITOR=emacs', `PATH=.:/gnubin:/hacks', and `DISPLAY=gnu:0'.
          env DISPLAY=gnu:0 LOGNAME=foo nemacs

   * Attempt to run the program `/energy/--' (as that is the only
     possible path search result); if the command exists, the
     environment will contain `LOGNAME=rms' and `PATH=/energy', and the
     arguments will be `e=mc2', `bar', and `baz'.
          env -u EDITOR PATH=/energy -- e=mc2 bar baz


   The program accepts the following options.  Also see *note Common
options::.  Options must precede operands.

`-0'
`--null'
     Output a zero byte (ASCII NUL) at the end of each line, rather
     than a newline. This option enables other programs to parse the
     output of `env' even when that output would contain data with
     embedded newlines.

`-u NAME'
`--unset=NAME'
     Remove variable NAME from the environment, if it was in the
     environment.

`-'
`-i'
`--ignore-environment'
     Start with an empty environment, ignoring the inherited
     environment.


   Exit status:

     0   if no COMMAND is specified and the environment is output
     125 if `env' itself fails
     126 if COMMAND is found but cannot be invoked
     127 if COMMAND cannot be found
     the exit status of COMMAND otherwise

File: coreutils.info,  Node: nice invocation,  Next: nohup invocation,  Prev: env invocation,  Up: Modified command invocation

23.3 `nice': Run a command with modified niceness
=================================================

`nice' prints or modifies a process's "niceness", a parameter that
affects whether the process is scheduled favorably.  Synopsis:

     nice [OPTION]... [COMMAND [ARG]...]

   If no arguments are given, `nice' prints the current niceness.
Otherwise, `nice' runs the given COMMAND with its niceness adjusted.
By default, its niceness is incremented by 10.

   Niceness values range at least from -20 (process has high priority
and gets more resources, thus slowing down other processes) through 19
(process has lower priority and runs slowly itself, but has less impact
on the speed of other running processes).  Some systems may have a
wider range of nicenesses; conversely, other systems may enforce more
restrictive limits.  An attempt to set the niceness outside the
supported range is treated as an attempt to use the minimum or maximum
supported value.

   A niceness should not be confused with a scheduling priority, which
lets applications determine the order in which threads are scheduled to
run.  Unlike a priority, a niceness is merely advice to the scheduler,
which the scheduler is free to ignore.  Also, as a point of
terminology, POSIX defines the behavior of `nice' in terms of a "nice
value", which is the nonnegative difference between a niceness and the
minimum niceness.  Though `nice' conforms to POSIX, its documentation
and diagnostics use the term "niceness" for compatibility with
historical practice.

   COMMAND must not be a special built-in utility (*note Special
built-in utilities::).

   Due to shell aliases and built-in `nice' command, using an unadorned
`nice' interactively or in a script may get you different functionality
than that described here.  Invoke it via `env' (i.e., `env nice ...')
to avoid interference from the shell.

   The program accepts the following option.  Also see *note Common
options::.  Options must precede operands.

`-n ADJUSTMENT'
`--adjustment=ADJUSTMENT'
     Add ADJUSTMENT instead of 10 to the command's niceness.  If
     ADJUSTMENT is negative and you lack appropriate privileges, `nice'
     issues a warning but otherwise acts as if you specified a zero
     adjustment.

     For compatibility `nice' also supports an obsolete option syntax
     `-ADJUSTMENT'.  New scripts should use `-n ADJUSTMENT' instead.


   Exit status:

     0   if no COMMAND is specified and the niceness is output
     125 if `nice' itself fails
     126 if COMMAND is found but cannot be invoked
     127 if COMMAND cannot be found
     the exit status of COMMAND otherwise

   It is sometimes useful to run a non-interactive program with reduced
niceness.

     $ nice factor 4611686018427387903

   Since `nice' prints the current niceness, you can invoke it through
itself to demonstrate how it works.

   The default behavior is to increase the niceness by `10':

     $ nice
     0
     $ nice nice
     10
     $ nice -n 10 nice
     10

   The ADJUSTMENT is relative to the current niceness.  In the next
example, the first `nice' invocation runs the second one with niceness
10, and it in turn runs the final one with a niceness that is 3 more:

     $ nice nice -n 3 nice
     13

   Specifying a niceness larger than the supported range is the same as
specifying the maximum supported value:

     $ nice -n 10000000000 nice
     19

   Only a privileged user may run a process with lower niceness:

     $ nice -n -1 nice
     nice: cannot set niceness: Permission denied
     0
     $ sudo nice -n -1 nice
     -1

File: coreutils.info,  Node: nohup invocation,  Next: stdbuf invocation,  Prev: nice invocation,  Up: Modified command invocation

23.4 `nohup': Run a command immune to hangups
=============================================

`nohup' runs the given COMMAND with hangup signals ignored, so that the
command can continue running in the background after you log out.
Synopsis:

     nohup COMMAND [ARG]...

   If standard input is a terminal, it is redirected from `/dev/null'
so that terminal sessions do not mistakenly consider the terminal to be
used by the command.  This is a GNU extension; programs intended to be
portable to non-GNU hosts should use `nohup COMMAND [ARG]... </dev/null'
instead.

   If standard output is a terminal, the command's standard output is
appended to the file `nohup.out'; if that cannot be written to, it is
appended to the file `$HOME/nohup.out'; and if that cannot be written
to, the command is not run.  Any `nohup.out' or `$HOME/nohup.out' file
created by `nohup' is made readable and writable only to the user,
regardless of the current umask settings.

   If standard error is a terminal, it is normally redirected to the
same file descriptor as the (possibly-redirected) standard output.
However, if standard output is closed, standard error terminal output
is instead appended to the file `nohup.out' or `$HOME/nohup.out' as
above.

   To capture the command's output to a file other than `nohup.out' you
can redirect it.  For example, to capture the output of `make':

     nohup make > make.log

   `nohup' does not automatically put the command it runs in the
background; you must do that explicitly, by ending the command line
with an `&'.  Also, `nohup' does not alter the niceness of COMMAND; use
`nice' for that, e.g., `nohup nice COMMAND'.

   COMMAND must not be a special built-in utility (*note Special
built-in utilities::).

   The only options are `--help' and `--version'.  *Note Common
options::.  Options must precede operands.

   Exit status:

     125 if `nohup' itself fails, and `POSIXLY_CORRECT' is not set
     126 if COMMAND is found but cannot be invoked
     127 if COMMAND cannot be found
     the exit status of COMMAND otherwise

   If `POSIXLY_CORRECT' is set, internal failures give status 127
instead of 125.

File: coreutils.info,  Node: stdbuf invocation,  Next: su invocation,  Prev: nohup invocation,  Up: Modified command invocation

23.5 `stdbuf': Run a command with modified I/O stream buffering
===============================================================

`stdbuf' allows one to modify the buffering operations of the three
standard I/O streams associated with a program.  Synopsis:

     stdbuf OPTION... COMMAND

   Any additional ARGs are passed as additional arguments to the
COMMAND.

   The program accepts the following options.  Also see *note Common
options::.

`-i MODE'
`--input=MODE'
     Adjust the standard input stream buffering.

`-o MODE'
`--output=MODE'
     Adjust the standard output stream buffering.

`-e MODE'
`--error=MODE'
     Adjust the standard error stream buffering.


   The MODE can be specified as follows:

`L'
     Set the stream to line buffered mode.  In this mode data is
     coalesced until a newline is output or input is read from any
     stream attached to a terminal device.  This option is invalid with
     standard input.

`0'
     Disable buffering of the selected stream.  In this mode data is
     output immediately and only the amount of data requested is read
     from input.

`SIZE'
     Specify the size of the buffer to use in fully buffered mode.
     SIZE may be, or may be an integer optionally followed by, one of
     the following multiplicative suffixes:
          `KB' =>           1000 (KiloBytes)
          `K'  =>           1024 (KibiBytes)
          `MB' =>      1000*1000 (MegaBytes)
          `M'  =>      1024*1024 (MebiBytes)
          `GB' => 1000*1000*1000 (GigaBytes)
          `G'  => 1024*1024*1024 (GibiBytes)
     and so on for `T', `P', `E', `Z', and `Y'.


   NOTE: If COMMAND adjusts the buffering of its standard streams
(`tee' does for e.g.) then that will override corresponding settings
changed by `stdbuf'.  Also some filters (like `dd' and `cat' etc.)
don't use streams for I/O, and are thus unaffected by `stdbuf' settings.

   Exit status:

     125 if `stdbuf' itself fails
     126 if COMMAND is found but cannot be invoked
     127 if COMMAND cannot be found
     the exit status of COMMAND otherwise

File: coreutils.info,  Node: su invocation,  Next: timeout invocation,  Prev: stdbuf invocation,  Up: Modified command invocation

23.6 `su': Run a command with substitute user and group ID
==========================================================

`su' allows one user to temporarily become another user.  It runs a
command (often an interactive shell) with the real and effective user
ID, group ID, and supplemental groups of a given USER. When the -l
option is given, the su-l PAM file is used instead of the default su
PAM file.  Synopsis:

     su [OPTION]... [USER [ARG]...]

   If no USER is given, the default is `root', the super-user.  The
shell to use is taken from USER's `passwd' entry, or `/bin/sh' if none
is specified there.  If USER has a password, `su' prompts for the
password unless run by a user with effective user ID of zero (the
super-user).

   By default, `su' does not change the current directory.  It sets the
environment variables `HOME' and `SHELL' from the password entry for
USER, and if USER is not the super-user, sets `USER' and `LOGNAME' to
USER.  By default, the shell is not a login shell.

   Any additional ARGs are passed as additional arguments to the shell.

   GNU `su' does not treat `/bin/sh' or any other shells specially
(e.g., by setting `argv[0]' to `-su', passing `-c' only to certain
shells, etc.).

   `su' can optionally be compiled to use `syslog' to report failed,
and optionally successful, `su' attempts.  (If the system supports
`syslog'.)

   This version of `su' has support for using PAM for authentication.
You can edit `/etc/pam.d/su' to customize its behaviour.

   The program accepts the following options.  Also see *note Common
options::.

`-c COMMAND'
`--command=COMMAND'
     Pass COMMAND, a single command line to run, to the shell with a
     `-c' option instead of starting an interactive shell.

`-f'
`--fast'
     Pass the `-f' option to the shell.  This probably only makes sense
     if the shell run is `csh' or `tcsh', for which the `-f' option
     prevents reading the startup file (`.cshrc').  With Bourne-like
     shells, the `-f' option disables file name pattern expansion
     (globbing), which is not likely to be useful.

`-'
`-l'
`--login'
     Make the shell a login shell.  This means the following.  Unset all
     environment variables except `TERM', `HOME', and `SHELL' (which
     are set as described above), and `USER' and `LOGNAME' (which are
     set, even for the super-user, as described above), and set `PATH'
     to a compiled-in default value.  Change to USER's home directory.
     Prepend `-' to the shell's name, intended to make it read its
     login startup file(s).  Additionaly `DISPLAY' and `XAUTHORITY'
     environment variables are preserved as well for PAM functionality.

`-m'
`-p'
`--preserve-environment'
     Do not change the environment variables `HOME', `USER', `LOGNAME',
     or `SHELL'.  Run the shell given in the environment variable
     `SHELL' instead of the shell from USER's passwd entry, unless the
     user running `su' is not the super-user and USER's shell is
     restricted.  A "restricted shell" is one that is not listed in the
     file `/etc/shells', or in a compiled-in list if that file does not
     exist.  Parts of what this option does can be overridden by
     `--login' and `--shell'.

`-s SHELL'
`--shell=SHELL'
     Run SHELL instead of the shell from USER's passwd entry, unless
     the user running `su' is not the super-user and USER's shell is
     restricted (see `-m' just above).


   Exit status:

     125 if `su' itself fails
     126 if subshell is found but cannot be invoked
     127 if subshell cannot be found
     the exit status of the subshell otherwise

File: coreutils.info,  Node: timeout invocation,  Prev: su invocation,  Up: Modified command invocation

23.7 `timeout': Run a command with a time limit
===============================================

`timeout' runs the given COMMAND and kills it if it is still running
after the specified time interval.  Synopsis:

     timeout [OPTION] NUMBER[smhd] COMMAND [ARG]...

   NUMBER is an integer followed by an optional unit; the default is
seconds.  The units are:

`s'
     seconds

`m'
     minutes

`h'
     hours

`d'
     days

   COMMAND must not be a special built-in utility (*note Special
built-in utilities::).

   The program accepts the following option.  Also see *note Common
options::.  Options must precede operands.

`-s SIGNAL'
`--signal=SIGNAL'
     Send this SIGNAL to COMMAND on timeout, rather than the default
     `TERM' signal. SIGNAL may be a name like `HUP' or a number. Also
     see *Note Signal specifications::.


   Exit status:

     124 if COMMAND times out
     125 if `timeout' itself fails
     126 if COMMAND is found but cannot be invoked
     127 if COMMAND cannot be found
     the exit status of COMMAND otherwise

File: coreutils.info,  Node: Process control,  Next: Delaying,  Prev: Modified command invocation,  Up: Top

24 Process control
******************

* Menu:

* kill invocation::             Sending a signal to processes.

File: coreutils.info,  Node: kill invocation,  Up: Process control

24.1 `kill': Send a signal to processes
=======================================

The `kill' command sends a signal to processes, causing them to
terminate or otherwise act upon receiving the signal in some way.
Alternatively, it lists information about signals.  Synopses:

     kill [-s SIGNAL | --signal SIGNAL | -SIGNAL] PID...
     kill [-l | --list | -t | --table] [SIGNAL]...

   Due to shell aliases and built-in `kill' command, using an unadorned
`kill' interactively or in a script may get you different functionality
than that described here.  Invoke it via `env' (i.e., `env kill ...')
to avoid interference from the shell.

   The first form of the `kill' command sends a signal to all PID
arguments.  The default signal to send if none is specified is `TERM'.
The special signal number `0' does not denote a valid signal, but can
be used to test whether the PID arguments specify processes to which a
signal could be sent.

   If PID is positive, the signal is sent to the process with the
process ID PID.  If PID is zero, the signal is sent to all processes in
the process group of the current process.  If PID is -1, the signal is
sent to all processes for which the user has permission to send a
signal.  If PID is less than -1, the signal is sent to all processes in
the process group that equals the absolute value of PID.

   If PID is not positive, a system-dependent set of system processes
is excluded from the list of processes to which the signal is sent.

   If a negative PID argument is desired as the first one, it should be
preceded by `--'.  However, as a common extension to POSIX, `--' is not
required with `kill -SIGNAL -PID'.  The following commands are
equivalent:

     kill -15 -1
     kill -TERM -1
     kill -s TERM -- -1
     kill -- -1

   The first form of the `kill' command succeeds if every PID argument
specifies at least one process that the signal was sent to.

   The second form of the `kill' command lists signal information.
Either the `-l' or `--list' option, or the `-t' or `--table' option
must be specified.  Without any SIGNAL argument, all supported signals
are listed.  The output of `-l' or `--list' is a list of the signal
names, one per line; if SIGNAL is already a name, the signal number is
printed instead.  The output of `-t' or `--table' is a table of signal
numbers, names, and descriptions.  This form of the `kill' command
succeeds if all SIGNAL arguments are valid and if there is no output
error.

   The `kill' command also supports the `--help' and `--version'
options.  *Note Common options::.

   A SIGNAL may be a signal name like `HUP', or a signal number like
`1', or an exit status of a process terminated by the signal.  A signal
name can be given in canonical form or prefixed by `SIG'.  The case of
the letters is ignored, except for the `-SIGNAL' option which must use
upper case to avoid ambiguity with lower case option letters.  For a
list of supported signal names and numbers see *Note Signal
specifications::.

File: coreutils.info,  Node: Delaying,  Next: Numeric operations,  Prev: Process control,  Up: Top

25 Delaying
***********

* Menu:

* sleep invocation::            Delay for a specified time.

File: coreutils.info,  Node: sleep invocation,  Up: Delaying

25.1 `sleep': Delay for a specified time
========================================

`sleep' pauses for an amount of time specified by the sum of the values
of the command line arguments.  Synopsis:

     sleep NUMBER[smhd]...

   Each argument is a number followed by an optional unit; the default
is seconds.  The units are:

`s'
     seconds

`m'
     minutes

`h'
     hours

`d'
     days

   Historical implementations of `sleep' have required that NUMBER be
an integer, and only accepted a single argument without a suffix.
However, GNU `sleep' accepts arbitrary floating point numbers (using a
period before any fractional digits).

   The only options are `--help' and `--version'.  *Note Common
options::.

   Due to shell aliases and built-in `sleep' command, using an
unadorned `sleep' interactively or in a script may get you different
functionality than that described here.  Invoke it via `env' (i.e.,
`env sleep ...') to avoid interference from the shell.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: Numeric operations,  Next: File permissions,  Prev: Delaying,  Up: Top

26 Numeric operations
*********************

These programs do numerically-related operations.

* Menu:

* factor invocation::              Show factors of numbers.
* seq invocation::                 Print sequences of numbers.

File: coreutils.info,  Node: factor invocation,  Next: seq invocation,  Up: Numeric operations

26.1 `factor': Print prime factors
==================================

`factor' prints prime factors.  Synopses:

     factor [NUMBER]...
     factor OPTION

   If no NUMBER is specified on the command line, `factor' reads
numbers from standard input, delimited by newlines, tabs, or spaces.

   The `factor' command supports only a small number of options:

`--help'
     Print a short help on standard output, then exit without further
     processing.

`--version'
     Print the program version on standard output, then exit without
     further processing.

   Factoring the product of the eighth and ninth Mersenne primes takes
about 30 milliseconds of CPU time on a 2.2 GHz Athlon.

     M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
     /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
     4951760154835678088235319297: 2147483647 2305843009213693951
     0.03

   Similarly, factoring the eighth Fermat number 2^256+1 takes about 20
seconds on the same machine.

   Factoring large prime numbers is, in general, hard.  The Pollard Rho
algorithm used by `factor' is particularly effective for numbers with
relatively small factors.  If you wish to factor large numbers which do
not have small factors (for example, numbers which are the product of
two large primes), other methods are far better.

   If `factor' is built without using GNU MP, only single-precision
arithmetic is available, and so large numbers (typically 2^64 and
above) will not be supported.  The single-precision code uses an
algorithm which is designed for factoring smaller numbers.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: seq invocation,  Prev: factor invocation,  Up: Numeric operations

26.2 `seq': Print numeric sequences
===================================

`seq' prints a sequence of numbers to standard output.  Synopses:

     seq [OPTION]... LAST
     seq [OPTION]... FIRST LAST
     seq [OPTION]... FIRST INCREMENT LAST

   `seq' prints the numbers from FIRST to LAST by INCREMENT.  By
default, each number is printed on a separate line.  When INCREMENT is
not specified, it defaults to `1', even when FIRST is larger than LAST.
FIRST also defaults to `1'.  So `seq 1' prints `1', but `seq 0' and
`seq 10 5' produce no output.  Floating-point numbers may be specified
(using a period before any fractional digits).

   The program accepts the following options.  Also see *note Common
options::.  Options must precede operands.

`-f FORMAT'
`--format=FORMAT'
     Print all numbers using FORMAT.  FORMAT must contain exactly one
     of the `printf'-style floating point conversion specifications
     `%a', `%e', `%f', `%g', `%A', `%E', `%F', `%G'.  The `%' may be
     followed by zero or more flags taken from the set `-+#0 '', then
     an optional width containing one or more digits, then an optional
     precision consisting of a `.' followed by zero or more digits.
     FORMAT may also contain any number of `%%' conversion
     specifications.  All conversion specifications have the same
     meaning as with `printf'.

     The default format is derived from FIRST, STEP, and LAST.  If
     these all use a fixed point decimal representation, the default
     format is `%.Pf', where P is the minimum precision that can
     represent the output numbers exactly.  Otherwise, the default
     format is `%g'.

`-s STRING'
`--separator=STRING'
     Separate numbers with STRING; default is a newline.  The output
     always terminates with a newline.

`-w'
`--equal-width'
     Print all numbers with the same width, by padding with leading
     zeros.  FIRST, STEP, and LAST should all use a fixed point decimal
     representation.  (To have other kinds of padding, use `--format').


   You can get finer-grained control over output with `-f':

     $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
     (-9.00E+05)
     ( 2.00E+05)
     ( 1.30E+06)

   If you want hexadecimal integer output, you can use `printf' to
perform the conversion:

     $ printf '%x\n' `seq 1048575 1024 1050623`
     fffff
     1003ff
     1007ff

   For very long lists of numbers, use xargs to avoid system
limitations on the length of an argument list:

     $ seq 1000000 | xargs printf '%x\n' | tail -n 3
     f423e
     f423f
     f4240

   To generate octal output, use the printf `%o' format instead of `%x'.

   On most systems, seq can produce whole-number output for values up to
at least 2^53.  Larger integers are approximated.  The details differ
depending on your floating-point implementation, but a common case is
that `seq' works with integers through 2^64, and larger integers may
not be numerically correct:

     $ seq 18446744073709551616 1 18446744073709551618
     18446744073709551616
     18446744073709551616
     18446744073709551618

   Be careful when using `seq' with outlandish values: otherwise you
may see surprising results, as `seq' uses floating point internally.
For example, on the x86 platform, where the internal representation
uses a 64-bit fraction, the command:

     seq 1 0.0000000000000000001 1.0000000000000000009

   outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

File: coreutils.info,  Node: File permissions,  Next: Date input formats,  Prev: Numeric operations,  Up: Top

27 File permissions
*******************

Each file has a set of "file mode bits" that control the kinds of
access that users have to that file.  They can be represented either in
symbolic form or as an octal number.

* Menu:

* Mode Structure::              Structure of file mode bits.
* Symbolic Modes::              Mnemonic representation of file mode bits.
* Numeric Modes::               File mode bits as octal numbers.
* Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories.

File: coreutils.info,  Node: Mode Structure,  Next: Symbolic Modes,  Up: File permissions

27.1 Structure of File Mode Bits
================================

The file mode bits have two parts: the "file permission bits", which
control ordinary access to the file, and "special mode bits", which
affect only some files.

   There are three kinds of permissions that a user can have for a file:

  1. permission to read the file.  For directories, this means
     permission to list the contents of the directory.

  2. permission to write to (change) the file.  For directories, this
     means permission to create and remove files in the directory.

  3. permission to execute the file (run it as a program).  For
     directories, this means permission to access files in the
     directory.

   There are three categories of users who may have different
permissions to perform any of the above operations on a file:

  1. the file's owner;

  2. other users who are in the file's group;

  3. everyone else.

   Files are given an owner and group when they are created.  Usually
the owner is the current user and the group is the group of the
directory the file is in, but this varies with the operating system, the
file system the file is created on, and the way the file is created.
You can change the owner and group of a file by using the `chown' and
`chgrp' commands.

   In addition to the three sets of three permissions listed above, the
file mode bits have three special components, which affect only
executable files (programs) and, on most systems, directories:

  1. Set the process's effective user ID to that of the file upon
     execution (called the "set-user-ID bit", or sometimes the "setuid
     bit").  For directories on a few systems, give files created in
     the directory the same owner as the directory, no matter who
     creates them, and set the set-user-ID bit of newly-created
     subdirectories.

  2. Set the process's effective group ID to that of the file upon
     execution (called the "set-group-ID bit", or sometimes the "setgid
     bit").  For directories on most systems, give files created in the
     directory the same group as the directory, no matter what group
     the user who creates them is in, and set the set-group-ID bit of
     newly-created subdirectories.

  3. Prevent unprivileged users from removing or renaming a file in a
     directory unless they own the file or the directory; this is
     called the "restricted deletion flag" for the directory, and is
     commonly found on world-writable directories like `/tmp'.

     For regular files on some older systems, save the program's text
     image on the swap device so it will load more quickly when run;
     this is called the "sticky bit".

   In addition to the file mode bits listed above, there may be file
attributes specific to the file system, e.g., access control lists
(ACLs), whether a file is compressed, whether a file can be modified
(immutability), and whether a file can be dumped.  These are usually
set using programs specific to the file system.  For example:

ext2
     On GNU and GNU/Linux the file attributes specific to the ext2 file
     system are set using `chattr'.

FFS
     On FreeBSD the file flags specific to the FFS file system are set
     using `chflags'.

   Even if a file's mode bits allow an operation on that file, that
operation may still fail, because:

   * the file-system-specific attributes or flags do not permit it; or

   * the file system is mounted as read-only.

   For example, if the immutable attribute is set on a file, it cannot
be modified, regardless of the fact that you may have just run `chmod
a+w FILE'.

File: coreutils.info,  Node: Symbolic Modes,  Next: Numeric Modes,  Prev: Mode Structure,  Up: File permissions

27.2 Symbolic Modes
===================

"Symbolic modes" represent changes to files' mode bits as operations on
single-character symbols.  They allow you to modify either all or
selected parts of files' mode bits, optionally based on their previous
values, and perhaps on the current `umask' as well (*note Umask and
Protection::).

   The format of symbolic modes is:

     [ugoa...][+-=]PERMS...[,...]

where PERMS is either zero or more letters from the set `rwxXst', or a
single letter from the set `ugo'.

   The following sections describe the operators and other details of
symbolic modes.

* Menu:

* Setting Permissions::          Basic operations on permissions.
* Copying Permissions::          Copying existing permissions.
* Changing Special Mode Bits::   Special mode bits.
* Conditional Executability::    Conditionally affecting executability.
* Multiple Changes::             Making multiple changes.
* Umask and Protection::              The effect of the umask.

File: coreutils.info,  Node: Setting Permissions,  Next: Copying Permissions,  Up: Symbolic Modes

27.2.1 Setting Permissions
--------------------------

The basic symbolic operations on a file's permissions are adding,
removing, and setting the permission that certain users have to read,
write, and execute or search the file.  These operations have the
following format:

     USERS OPERATION PERMISSIONS

The spaces between the three parts above are shown for readability only;
symbolic modes cannot contain spaces.

   The USERS part tells which users' access to the file is changed.  It
consists of one or more of the following letters (or it can be empty;
*note Umask and Protection::, for a description of what happens then).
When more than one of these letters is given, the order that they are
in does not matter.

`u'
     the user who owns the file;

`g'
     other users who are in the file's group;

`o'
     all other users;

`a'
     all users; the same as `ugo'.

   The OPERATION part tells how to change the affected users' access to
the file, and is one of the following symbols:

`+'
     to add the PERMISSIONS to whatever permissions the USERS already
     have for the file;

`-'
     to remove the PERMISSIONS from whatever permissions the USERS
     already have for the file;

`='
     to make the PERMISSIONS the only permissions that the USERS have
     for the file.

   The PERMISSIONS part tells what kind of access to the file should be
changed; it is normally zero or more of the following letters.  As with
the USERS part, the order does not matter when more than one letter is
given.  Omitting the PERMISSIONS part is useful only with the `='
operation, where it gives the specified USERS no access at all to the
file.

`r'
     the permission the USERS have to read the file;

`w'
     the permission the USERS have to write to the file;

`x'
     the permission the USERS have to execute the file, or search it if
     it is a directory.

   For example, to give everyone permission to read and write a regular
file, but not to execute it, use:

     a=rw

   To remove write permission for all users other than the file's
owner, use:

     go-w

The above command does not affect the access that the owner of the file
has to it, nor does it affect whether other users can read or execute
the file.

   To give everyone except a file's owner no permission to do anything
with that file, use the mode below.  Other users could still remove the
file, if they have write permission on the directory it is in.

     go=

Another way to specify the same thing is:

     og-rwx

File: coreutils.info,  Node: Copying Permissions,  Next: Changing Special Mode Bits,  Prev: Setting Permissions,  Up: Symbolic Modes

27.2.2 Copying Existing Permissions
-----------------------------------

You can base a file's permissions on its existing permissions.  To do
this, instead of using a series of `r', `w', or `x' letters after the
operator, you use the letter `u', `g', or `o'.  For example, the mode

     o+g

adds the permissions for users who are in a file's group to the
permissions that other users have for the file.  Thus, if the file
started out as mode 664 (`rw-rw-r--'), the above mode would change it
to mode 666 (`rw-rw-rw-').  If the file had started out as mode 741
(`rwxr----x'), the above mode would change it to mode 745
(`rwxr--r-x').  The `-' and `=' operations work analogously.

File: coreutils.info,  Node: Changing Special Mode Bits,  Next: Conditional Executability,  Prev: Copying Permissions,  Up: Symbolic Modes

27.2.3 Changing Special Mode Bits
---------------------------------

In addition to changing a file's read, write, and execute/search
permissions, you can change its special mode bits.  *Note Mode
Structure::, for a summary of these special mode bits.

   To change the file mode bits to set the user ID on execution, use
`u' in the USERS part of the symbolic mode and `s' in the PERMISSIONS
part.

   To change the file mode bits to set the group ID on execution, use
`g' in the USERS part of the symbolic mode and `s' in the PERMISSIONS
part.

   To set both user and group ID on execution, omit the USERS part of
the symbolic mode (or use `a') and use `s' in the PERMISSIONS part.

   To change the file mode bits to set the restricted deletion flag or
sticky bit, omit the USERS part of the symbolic mode (or use `a') and
use `t' in the PERMISSIONS part.

   For example, to set the set-user-ID mode bit of a program, you can
use the mode:

     u+s

   To remove both set-user-ID and set-group-ID mode bits from it, you
can use the mode:

     a-s

   To set the restricted deletion flag or sticky bit, you can use the
mode:

     +t

   The combination `o+s' has no effect.  On GNU systems the
combinations `u+t' and `g+t' have no effect, and `o+t' acts like plain
`+t'.

   The `=' operator is not very useful with special mode bits.  For
example, the mode:

     o=t

does set the restricted deletion flag or sticky bit, but it also
removes all read, write, and execute/search permissions that users not
in the file's group might have had for it.

   *Note Directory Setuid and Setgid::, for additional rules concerning
set-user-ID and set-group-ID bits and directories.

File: coreutils.info,  Node: Conditional Executability,  Next: Multiple Changes,  Prev: Changing Special Mode Bits,  Up: Symbolic Modes

27.2.4 Conditional Executability
--------------------------------

There is one more special type of symbolic permission: if you use `X'
instead of `x', execute/search permission is affected only if the file
is a directory or already had execute permission.

   For example, this mode:

     a+X

gives all users permission to search directories, or to execute files if
anyone could execute them before.

File: coreutils.info,  Node: Multiple Changes,  Next: Umask and Protection,  Prev: Conditional Executability,  Up: Symbolic Modes

27.2.5 Making Multiple Changes
------------------------------

The format of symbolic modes is actually more complex than described
above (*note Setting Permissions::).  It provides two ways to make
multiple changes to files' mode bits.

   The first way is to specify multiple OPERATION and PERMISSIONS parts
after a USERS part in the symbolic mode.

   For example, the mode:

     og+rX-w

gives users other than the owner of the file read permission and, if it
is a directory or if someone already had execute permission to it,
gives them execute/search permission; and it also denies them write
permission to the file.  It does not affect the permission that the
owner of the file has for it.  The above mode is equivalent to the two
modes:

     og+rX
     og-w

   The second way to make multiple changes is to specify more than one
simple symbolic mode, separated by commas.  For example, the mode:

     a+r,go-w

gives everyone permission to read the file and removes write permission
on it for all users except its owner.  Another example:

     u=rwx,g=rx,o=

sets all of the permission bits for the file explicitly.  (It gives
users who are not in the file's group no permission at all for it.)

   The two methods can be combined.  The mode:

     a+r,g+x-w

gives all users permission to read the file, and gives users who are in
the file's group permission to execute/search it as well, but not
permission to write to it.  The above mode could be written in several
different ways; another is:

     u+r,g+rx,o+r,g-w

File: coreutils.info,  Node: Umask and Protection,  Prev: Multiple Changes,  Up: Symbolic Modes

27.2.6 The Umask and Protection
-------------------------------

If the USERS part of a symbolic mode is omitted, it defaults to `a'
(affect all users), except that any permissions that are _set_ in the
system variable `umask' are _not affected_.  The value of `umask' can
be set using the `umask' command.  Its default value varies from system
to system.

   Omitting the USERS part of a symbolic mode is generally not useful
with operations other than `+'.  It is useful with `+' because it
allows you to use `umask' as an easily customizable protection against
giving away more permission to files than you intended to.

   As an example, if `umask' has the value 2, which removes write
permission for users who are not in the file's group, then the mode:

     +w

adds permission to write to the file to its owner and to other users who
are in the file's group, but _not_ to other users.  In contrast, the
mode:

     a+w

ignores `umask', and _does_ give write permission for the file to all
users.

File: coreutils.info,  Node: Numeric Modes,  Next: Directory Setuid and Setgid,  Prev: Symbolic Modes,  Up: File permissions

27.3 Numeric Modes
==================

As an alternative to giving a symbolic mode, you can give an octal
(base 8) number that represents the mode.  This number is always
interpreted in octal; you do not have to add a leading `0', as you do
in C.  Mode `0055' is the same as mode `55'. However, adding leading
zeros to create octal number with at least 5 digits means that this
mode is taken explicitly - so could clear even the set-user-ID and
set-group-ID bits of directories.

   A numeric mode is usually shorter than the corresponding symbolic
mode, but it is limited in that normally it cannot take into account the
previous file mode bits; it can only set them absolutely.  (As
discussed in the next section, the set-user-ID and set-group-ID bits of
directories are an exception to this general limitation.)

   The permissions granted to the user, to other users in the file's
group, and to other users not in the file's group each require three
bits, which are represented as one octal digit.  The three special mode
bits also require one bit each, and they are as a group represented as
another octal digit.  Here is how the bits are arranged, starting with
the lowest valued bit:

     Value in  Corresponding
     Mode      Mode Bit

               Other users not in the file's group:
        1      Execute/search
        2      Write
        4      Read

               Other users in the file's group:
       10      Execute/search
       20      Write
       40      Read

               The file's owner:
      100      Execute/search
      200      Write
      400      Read

               Special mode bits:
     1000      Restricted deletion flag or sticky bit
     2000      Set group ID on execution
     4000      Set user ID on execution

   For example, numeric mode `4755' corresponds to symbolic mode
`u=rwxs,go=rx', and numeric mode `664' corresponds to symbolic mode
`ug=rw,o=r'.  Numeric mode `0' corresponds to symbolic mode `a='.

File: coreutils.info,  Node: Directory Setuid and Setgid,  Prev: Numeric Modes,  Up: File permissions

27.4 Directories and the Set-User-ID and Set-Group-ID Bits
==========================================================

On most systems, if a directory's set-group-ID bit is set, newly
created subfiles inherit the same group as the directory, and newly
created subdirectories inherit the set-group-ID bit of the parent
directory.  On a few systems, a directory's set-user-ID bit has a
similar effect on the ownership of new subfiles and the set-user-ID
bits of new subdirectories.  These mechanisms let users share files
more easily, by lessening the need to use `chmod' or `chown' to share
new files.

   These convenience mechanisms rely on the set-user-ID and set-group-ID
bits of directories.  If commands like `chmod' and `mkdir' routinely
cleared these bits on directories, the mechanisms would be less
convenient and it would be harder to share files.  Therefore, a command
like `chmod' does not affect the set-user-ID or set-group-ID bits of a
directory unless the user specifically mentions them in a symbolic
mode, explicitly enforces the mode by at least 5 digits long octal
mode, or when sets them in a numeric mode.

   For example, on systems that support set-group-ID inheritance:

     # These commands leave the set-user-ID and
     # set-group-ID bits of the subdirectories alone,
     # so that they retain their default values.
     mkdir A B C
     chmod 755 A
     chmod 0755 B
     chmod u=rwx,go=rx C
     mkdir -m 755 D
     mkdir -m 0755 E
     mkdir -m u=rwx,go=rx F

   If you want to try to set these bits, you must mention them
explicitly in the symbolic or numeric modes, e.g.:

     # These commands try to set the set-user-ID
     # and set-group-ID bits of the subdirectories.
     mkdir G H
     chmod 6755 G
     chmod u=rwx,go=rx,a+s H
     mkdir -m 6755 I
     mkdir -m u=rwx,go=rx,a+s J

   If you want to try to clear these bits, you must mention them
explicitly in a symbolic mode, e.g.:

     # This command tries to clear the set-user-ID
     # and set-group-ID bits of the directory D.
     chmod a-s D

   If you want force the chmod to change directory mode to exact
numeric mode (clear the special bits), you could use at least 5 digit
octal mode, e.g.:

     # This command tries to clear the set-user-ID
     # and set-group-ID bits of the directory D and set
     # its permissions to 0755.
     chmod 00755 D

   This behavior is a GNU extension.  Portable scripts should not rely
on requests to set or clear these bits on directories, as POSIX allows
implementations to ignore these requests.

File: coreutils.info,  Node: Opening the software toolbox,  Next: GNU Free Documentation License,  Prev: Date input formats,  Up: Top

29 Opening the Software Toolbox
*******************************

An earlier version of this chapter appeared in 2 (June 1994).  It was
written by Arnold Robbins.

* Menu:

* Toolbox introduction::        Toolbox introduction
* I/O redirection::             I/O redirection
* The who command::             The `who' command
* The cut command::             The `cut' command
* The sort command::            The `sort' command
* The uniq command::            The `uniq' command
* Putting the tools together::  Putting the tools together

File: coreutils.info,  Node: Toolbox introduction,  Next: I/O redirection,  Up: Opening the software toolbox

Toolbox Introduction
====================

This month's column is only peripherally related to the GNU Project, in
that it describes a number of the GNU tools on your GNU/Linux system
and how they might be used.  What it's really about is the "Software
Tools" philosophy of program development and usage.

   The software tools philosophy was an important and integral concept
in the initial design and development of Unix (of which Linux and GNU
are essentially clones).  Unfortunately, in the modern day press of
Internetworking and flashy GUIs, it seems to have fallen by the
wayside.  This is a shame, since it provides a powerful mental model
for solving many kinds of problems.

   Many people carry a Swiss Army knife around in their pants pockets
(or purse).  A Swiss Army knife is a handy tool to have: it has several
knife blades, a screwdriver, tweezers, toothpick, nail file, corkscrew,
and perhaps a number of other things on it.  For the everyday, small
miscellaneous jobs where you need a simple, general purpose tool, it's
just the thing.

   On the other hand, an experienced carpenter doesn't build a house
using a Swiss Army knife.  Instead, he has a toolbox chock full of
specialized tools--a saw, a hammer, a screwdriver, a plane, and so on.
And he knows exactly when and where to use each tool; you won't catch
him hammering nails with the handle of his screwdriver.

   The Unix developers at Bell Labs were all professional programmers
and trained computer scientists.  They had found that while a
one-size-fits-all program might appeal to a user because there's only
one program to use, in practice such programs are

  a. difficult to write,

  b. difficult to maintain and debug, and

  c. difficult to extend to meet new situations.

   Instead, they felt that programs should be specialized tools.  In
short, each program "should do one thing well."  No more and no less.
Such programs are simpler to design, write, and get right--they only do
one thing.

   Furthermore, they found that with the right machinery for hooking
programs together, that the whole was greater than the sum of the
parts.  By combining several special purpose programs, you could
accomplish a specific task that none of the programs was designed for,
and accomplish it much more quickly and easily than if you had to write
a special purpose program.  We will see some (classic) examples of this
further on in the column.  (An important additional point was that, if
necessary, take a detour and build any software tools you may need
first, if you don't already have something appropriate in the toolbox.)

File: coreutils.info,  Node: I/O redirection,  Next: The who command,  Prev: Toolbox introduction,  Up: Opening the software toolbox

I/O Redirection
===============

Hopefully, you are familiar with the basics of I/O redirection in the
shell, in particular the concepts of "standard input," "standard
output," and "standard error".  Briefly, "standard input" is a data
source, where data comes from.  A program should not need to either
know or care if the data source is a disk file, a keyboard, a magnetic
tape, or even a punched card reader.  Similarly, "standard output" is a
data sink, where data goes to.  The program should neither know nor
care where this might be.  Programs that only read their standard
input, do something to the data, and then send it on, are called
"filters", by analogy to filters in a water pipeline.

   With the Unix shell, it's very easy to set up data pipelines:

     program_to_create_data | filter1 | ... | filterN > final.pretty.data

   We start out by creating the raw data; each filter applies some
successive transformation to the data, until by the time it comes out
of the pipeline, it is in the desired form.

   This is fine and good for standard input and standard output.  Where
does the standard error come in to play?  Well, think about `filter1' in
the pipeline above.  What happens if it encounters an error in the data
it sees?  If it writes an error message to standard output, it will just
disappear down the pipeline into `filter2''s input, and the user will
probably never see it.  So programs need a place where they can send
error messages so that the user will notice them.  This is standard
error, and it is usually connected to your console or window, even if
you have redirected standard output of your program away from your
screen.

   For filter programs to work together, the format of the data has to
be agreed upon.  The most straightforward and easiest format to use is
simply lines of text.  Unix data files are generally just streams of
bytes, with lines delimited by the ASCII LF (Line Feed) character,
conventionally called a "newline" in the Unix literature.  (This is
`'\n'' if you're a C programmer.)  This is the format used by all the
traditional filtering programs.  (Many earlier operating systems had
elaborate facilities and special purpose programs for managing binary
data.  Unix has always shied away from such things, under the
philosophy that it's easiest to simply be able to view and edit your
data with a text editor.)

   OK, enough introduction.  Let's take a look at some of the tools,
and then we'll see how to hook them together in interesting ways.   In
the following discussion, we will only present those command line
options that interest us.  As you should always do, double check your
system documentation for the full story.

File: coreutils.info,  Node: The who command,  Next: The cut command,  Prev: I/O redirection,  Up: Opening the software toolbox

The `who' Command
=================

The first program is the `who' command.  By itself, it generates a list
of the users who are currently logged in.  Although I'm writing this on
a single-user system, we'll pretend that several people are logged in:

     $ who
     -| arnold   console Jan 22 19:57
     -| miriam   ttyp0   Jan 23 14:19(:0.0)
     -| bill     ttyp1   Jan 21 09:32(:0.0)
     -| arnold   ttyp2   Jan 23 20:48(:0.0)

   Here, the `$' is the usual shell prompt, at which I typed `who'.
There are three people logged in, and I am logged in twice.  On
traditional Unix systems, user names are never more than eight
characters long.  This little bit of trivia will be useful later.  The
output of `who' is nice, but the data is not all that exciting.

File: coreutils.info,  Node: The cut command,  Next: The sort command,  Prev: The who command,  Up: Opening the software toolbox

The `cut' Command
=================

The next program we'll look at is the `cut' command.  This program cuts
out columns or fields of input data.  For example, we can tell it to
print just the login name and full name from the `/etc/passwd' file.
The `/etc/passwd' file has seven fields, separated by colons:

     arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash

   To get the first and fifth fields, we would use `cut' like this:

     $ cut -d: -f1,5 /etc/passwd
     -| root:Operator
     ...
     -| arnold:Arnold D. Robbins
     -| miriam:Miriam A. Robbins
     ...

   With the `-c' option, `cut' will cut out specific characters (i.e.,
columns) in the input lines.  This is useful for input data that has
fixed width fields, and does not have a field separator.  For example,
list the Monday dates for the current month:

     $ cal | cut -c 3-5
     -|Mo
     -|
     -|  6
     -| 13
     -| 20
     -| 27

File: coreutils.info,  Node: The sort command,  Next: The uniq command,  Prev: The cut command,  Up: Opening the software toolbox

The `sort' Command
==================

Next we'll look at the `sort' command.  This is one of the most
powerful commands on a Unix-style system; one that you will often find
yourself using when setting up fancy data plumbing.

   The `sort' command reads and sorts each file named on the command
line.  It then merges the sorted data and writes it to standard output.
It will read standard input if no files are given on the command line
(thus making it into a filter).  The sort is based on the character
collating sequence or based on user-supplied ordering criteria.

File: coreutils.info,  Node: The uniq command,  Next: Putting the tools together,  Prev: The sort command,  Up: Opening the software toolbox

The `uniq' Command
==================

Finally (at least for now), we'll look at the `uniq' program.  When
sorting data, you will often end up with duplicate lines, lines that
are identical.  Usually, all you need is one instance of each line.
This is where `uniq' comes in.  The `uniq' program reads its standard
input.  It prints only one copy of each repeated line.  It does have
several options.  Later on, we'll use the `-c' option, which prints
each unique line, preceded by a count of the number of times that line
occurred in the input.

File: coreutils.info,  Node: Putting the tools together,  Prev: The uniq command,  Up: Opening the software toolbox

Putting the Tools Together
==========================

Now, let's suppose this is a large ISP server system with dozens of
users logged in.  The management wants the system administrator to
write a program that will generate a sorted list of logged in users.
Furthermore, even if a user is logged in multiple times, his or her
name should only show up in the output once.

   The administrator could sit down with the system documentation and
write a C program that did this.  It would take perhaps a couple of
hundred lines of code and about two hours to write it, test it, and
debug it.  However, knowing the software toolbox, the administrator can
instead start out by generating just a list of logged on users:

     $ who | cut -c1-8
     -| arnold
     -| miriam
     -| bill
     -| arnold

   Next, sort the list:

     $ who | cut -c1-8 | sort
     -| arnold
     -| arnold
     -| bill
     -| miriam

   Finally, run the sorted list through `uniq', to weed out duplicates:

     $ who | cut -c1-8 | sort | uniq
     -| arnold
     -| bill
     -| miriam

   The `sort' command actually has a `-u' option that does what `uniq'
does.  However, `uniq' has other uses for which one cannot substitute
`sort -u'.

   The administrator puts this pipeline into a shell script, and makes
it available for all the users on the system (`#' is the system
administrator, or `root', prompt):

     # cat > /usr/local/bin/listusers
     who | cut -c1-8 | sort | uniq
     ^D
     # chmod +x /usr/local/bin/listusers

   There are four major points to note here.  First, with just four
programs, on one command line, the administrator was able to save about
two hours worth of work.  Furthermore, the shell pipeline is just about
as efficient as the C program would be, and it is much more efficient in
terms of programmer time.  People time is much more expensive than
computer time, and in our modern "there's never enough time to do
everything" society, saving two hours of programmer time is no mean
feat.

   Second, it is also important to emphasize that with the
_combination_ of the tools, it is possible to do a special purpose job
never imagined by the authors of the individual programs.

   Third, it is also valuable to build up your pipeline in stages, as
we did here.  This allows you to view the data at each stage in the
pipeline, which helps you acquire the confidence that you are indeed
using these tools correctly.

   Finally, by bundling the pipeline in a shell script, other users can
use your command, without having to remember the fancy plumbing you set
up for them.  In terms of how you run them, shell scripts and compiled
programs are indistinguishable.

   After the previous warm-up exercise, we'll look at two additional,
more complicated pipelines.  For them, we need to introduce two more
tools.

   The first is the `tr' command, which stands for "transliterate."
The `tr' command works on a character-by-character basis, changing
characters.  Normally it is used for things like mapping upper case to
lower case:

     $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
     -| this example has mixed case!

   There are several options of interest:

`-c'
     work on the complement of the listed characters, i.e., operations
     apply to characters not in the given set

`-d'
     delete characters in the first set from the output

`-s'
     squeeze repeated characters in the output into just one character.

   We will be using all three options in a moment.

   The other command we'll look at is `comm'.  The `comm' command takes
two sorted input files as input data, and prints out the files' lines
in three columns.  The output columns are the data lines unique to the
first file, the data lines unique to the second file, and the data
lines that are common to both.  The `-1', `-2', and `-3' command line
options _omit_ the respective columns.  (This is non-intuitive and
takes a little getting used to.)  For example:

     $ cat f1
     -| 11111
     -| 22222
     -| 33333
     -| 44444
     $ cat f2
     -| 00000
     -| 22222
     -| 33333
     -| 55555
     $ comm f1 f2
     -|         00000
     -| 11111
     -|                 22222
     -|                 33333
     -| 44444
     -|         55555

   The file name `-' tells `comm' to read standard input instead of a
regular file.

   Now we're ready to build a fancy pipeline.  The first application is
a word frequency counter.  This helps an author determine if he or she
is over-using certain words.

   The first step is to change the case of all the letters in our input
file to one case.  "The" and "the" are the same word when doing
counting.

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...

   The next step is to get rid of punctuation.  Quoted words and
unquoted words should be treated identically; it's easiest to just get
the punctuation out of the way.

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...

   The second `tr' command operates on the complement of the listed
characters, which are all the letters, the digits, the underscore, and
the blank.  The `\n' represents the newline character; it has to be
left alone.  (The ASCII tab character should also be included for good
measure in a production script.)

   At this point, we have data consisting of words separated by blank
space.  The words only contain alphanumeric characters (and the
underscore).  The next step is break the data apart so that we have one
word per line.  This makes the counting operation much easier, as we
will see shortly.

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
     > tr -s ' ' '\n' | ...

   This command turns blanks into newlines.  The `-s' option squeezes
multiple newline characters in the output into just one.  This helps us
avoid blank lines.  (The `>' is the shell's "secondary prompt."  This
is what the shell prints when it notices you haven't finished typing in
all of a command.)

   We now have data consisting of one word per line, no punctuation,
all one case.  We're ready to count each word:

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
     > tr -s ' ' '\n' | sort | uniq -c | ...

   At this point, the data might look something like this:

          60 a
           2 able
           6 about
           1 above
           2 accomplish
           1 acquire
           1 actually
           2 additional

   The output is sorted by word, not by count!  What we want is the most
frequently used words first.  Fortunately, this is easy to accomplish,
with the help of two more `sort' options:

`-n'
     do a numeric sort, not a textual one

`-r'
     reverse the order of the sort

   The final pipeline looks like this:

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
     > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
     -|    156 the
     -|     60 a
     -|     58 to
     -|     51 of
     -|     51 and
     ...

   Whew!  That's a lot to digest.  Yet, the same principles apply.
With six commands, on two lines (really one long one split for
convenience), we've created a program that does something interesting
and useful, in much less time than we could have written a C program to
do the same thing.

   A minor modification to the above pipeline can give us a simple
spelling checker!  To determine if you've spelled a word correctly, all
you have to do is look it up in a dictionary.  If it is not there, then
chances are that your spelling is incorrect.  So, we need a dictionary.
The conventional location for a dictionary is `/usr/dict/words'.  On my
GNU/Linux system,(1) this is a sorted, 45,402 word dictionary.

   Now, how to compare our file with the dictionary?  As before, we
generate a sorted list of words, one per line:

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
     > tr -s ' ' '\n' | sort -u | ...

   Now, all we need is a list of words that are _not_ in the
dictionary.  Here is where the `comm' command comes in.

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
     > tr -s ' ' '\n' | sort -u |
     > comm -23 - /usr/dict/words

   The `-2' and `-3' options eliminate lines that are only in the
dictionary (the second file), and lines that are in both files.  Lines
only in the first file (standard input, our stream of words), are words
that are not in the dictionary.  These are likely candidates for
spelling errors.  This pipeline was the first cut at a production
spelling checker on Unix.

   There are some other tools that deserve brief mention.

`grep'
     search files for text that matches a regular expression

`wc'
     count lines, words, characters

`tee'
     a T-fitting for data pipes, copies data to files and to standard
     output

`sed'
     the stream editor, an advanced tool

`awk'
     a data manipulation language, another advanced tool

   The software tools philosophy also espoused the following bit of
advice: "Let someone else do the hard part."  This means, take
something that gives you most of what you need, and then massage it the
rest of the way until it's in the form that you want.

   To summarize:

  1. Each program should do one thing well.  No more, no less.

  2. Combining programs with appropriate plumbing leads to results where
     the whole is greater than the sum of the parts.  It also leads to
     novel uses of programs that the authors might never have imagined.

  3. Programs should never print extraneous header or trailer data,
     since these could get sent on down a pipeline.  (A point we didn't
     mention earlier.)

  4. Let someone else do the hard part.

  5. Know your toolbox!  Use each program appropriately.  If you don't
     have an appropriate tool, build one.

   As of this writing, all the programs we've discussed are available
via anonymous `ftp' from:
`ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz'.  (There may be
more recent versions available now.)

   None of what I have presented in this column is new.  The Software
Tools philosophy was first introduced in the book `Software Tools', by
Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
This book showed how to write and use software tools.  It was written in
1976, using a preprocessor for FORTRAN named `ratfor' (RATional
FORtran).  At the time, C was not as ubiquitous as it is now; FORTRAN
was.  The last chapter presented a `ratfor' to FORTRAN processor,
written in `ratfor'.  `ratfor' looks an awful lot like C; if you know
C, you won't have any problem following the code.

   In 1981, the book was updated and made available as `Software Tools
in Pascal' (Addison-Wesley, ISBN 0-201-10342-7).  Both books are still
in print and are well worth reading if you're a programmer.  They
certainly made a major change in how I view programming.

   The programs in both books are available from Brian Kernighan's home
page (http://cm.bell-labs.com/who/bwk).  For a number of years, there
was an active Software Tools Users Group, whose members had ported the
original `ratfor' programs to essentially every computer system with a
FORTRAN compiler.  The popularity of the group waned in the middle 1980s
as Unix began to spread beyond universities.

   With the current proliferation of GNU code and other clones of Unix
programs, these programs now receive little attention; modern C
versions are much more efficient and do more than these programs do.
Nevertheless, as exposition of good programming style, and evangelism
for a still-valuable philosophy, these books are unparalleled, and I
recommend them highly.

   Acknowledgment: I would like to express my gratitude to Brian
Kernighan of Bell Labs, the original Software Toolsmith, for reviewing
this column.

   ---------- Footnotes ----------

   (1) Redhat Linux 6.1, for the November 2000 revision of this article.

File: coreutils.info,  Node: GNU Free Documentation License,  Next: Concept index,  Prev: Opening the software toolbox,  Up: Top

Appendix A GNU Free Documentation License
*****************************************

                     Version 1.3, 3 November 2008

     Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     `http://fsf.org/'

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     functional and useful document "free" in the sense of freedom: to
     assure everyone the effective freedom to copy and redistribute it,
     with or without modifying it, either commercially or
     noncommercially.  Secondarily, this License preserves for the
     author and publisher a way to get credit for their work, while not
     being considered responsible for modifications made by others.

     This License is a kind of "copyleft", which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
     that the software does.  But this License is not limited to
     software manuals; it can be used for any textual work, regardless
     of subject matter or whether it is published as a printed book.
     We recommend this License principally for works whose purpose is
     instruction or reference.

  1. APPLICABILITY AND DEFINITIONS

     This License applies to any manual or other work, in any medium,
     that contains a notice placed by the copyright holder saying it
     can be distributed under the terms of this License.  Such a notice
     grants a world-wide, royalty-free license, unlimited in duration,
     to use that work under the conditions stated herein.  The
     "Document", below, refers to any such manual or work.  Any member
     of the public is a licensee, and is addressed as "you".  You
     accept the license if you copy, modify or distribute the work in a
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     A "Modified Version" of the Document means any work containing the
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     A "Secondary Section" is a named appendix or a front-matter section
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     The "Invariant Sections" are certain Secondary Sections whose
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     The "Cover Texts" are certain short passages of text that are
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     implication that these Warranty Disclaimers may have is void and
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  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
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     You may also lend copies, under the same conditions stated above,
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  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
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     If the required texts for either cover are too voluminous to fit
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     adjacent pages.

     If you publish or distribute Opaque copies of the Document
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     state in or with each Opaque copy a computer-network location from
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     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of
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  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with
     the Modified Version filling the role of the Document, thus
     licensing distribution and modification of the Modified Version to
     whoever possesses a copy of it.  In addition, you must do these
     things in the Modified Version:

       A. Use in the Title Page (and on the covers, if any) a title
          distinct from that of the Document, and from those of
          previous versions (which should, if there were any, be listed
          in the History section of the Document).  You may use the
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       B. List on the Title Page, as authors, one or more persons or
          entities responsible for authorship of the modifications in
          the Modified Version, together with at least five of the
          principal authors of the Document (all of its principal
          authors, if it has fewer than five), unless they release you
          from this requirement.

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. Include, immediately after the copyright notices, a license
          notice giving the public permission to use the Modified
          Version under the terms of this License, in the form shown in
          the Addendum below.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document's
          license notice.

       H. Include an unaltered copy of this License.

       I. Preserve the section Entitled "History", Preserve its Title,
          and add to it an item stating at least the title, year, new
          authors, and publisher of the Modified Version as given on
          the Title Page.  If there is no section Entitled "History" in
          the Document, create one stating the title, year, authors,
          and publisher of the Document as given on its Title Page,
          then add an item describing the Modified Version as stated in
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       J. Preserve the network location, if any, given in the Document
          for public access to a Transparent copy of the Document, and
          likewise the network locations given in the Document for
          previous versions it was based on.  These may be placed in
          the "History" section.  You may omit a network location for a
          work that was published at least four years before the
          Document itself, or if the original publisher of the version
          it refers to gives permission.

       K. For any section Entitled "Acknowledgements" or "Dedications",
          Preserve the Title of the section, and preserve in the
          section all the substance and tone of each of the contributor
          acknowledgements and/or dedications given therein.

       L. Preserve all the Invariant Sections of the Document,
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          or the equivalent are not considered part of the section
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       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
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     designate some or all of these sections as invariant.  To do this,
     add their titles to the list of Invariant Sections in the Modified
     Version's license notice.  These titles must be distinct from any
     other section titles.

     You may add a section Entitled "Endorsements", provided it contains
     nothing but endorsements of your Modified Version by various
     parties--for example, statements of peer review or that the text
     has been approved by an organization as the authoritative
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     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end
     of the list of Cover Texts in the Modified Version.  Only one
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     added by (or through arrangements made by) any one entity.  If the
     Document already includes a cover text for the same cover,
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     replace the old one, on explicit permission from the previous
     publisher that added the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination
     all of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
     but different contents, make the title of each such section unique
     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections Entitled
     "History" in the various original documents, forming one section
     Entitled "History"; likewise combine any sections Entitled
     "Acknowledgements", and any sections Entitled "Dedications".  You
     must delete all sections Entitled "Endorsements."

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the
     documents in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow
     this License in all other respects regarding verbatim copying of
     that document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of
     a storage or distribution medium, is called an "aggregate" if the
     copyright resulting from the compilation is not used to limit the
     legal rights of the compilation's users beyond what the individual
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     If the Cover Text requirement of section 3 is applicable to these
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  8. TRANSLATION

     Translation is considered a kind of modification, so you may
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     translation of this License, and all the license notices in the
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     If a section in the Document is Entitled "Acknowledgements",
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     Preserve its Title (section 1) will typically require changing the
     actual title.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided under this License.  Any attempt
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     Moreover, your license from a particular copyright holder is
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     Termination of your rights under this section does not terminate
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     the same material does not give you any rights to use it.

 10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
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     Each version of the License is given a distinguishing version
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     proxy's public statement of acceptance of a version permanently
     authorizes you to choose that version for the Document.

 11. RELICENSING

     "Massive Multiauthor Collaboration Site" (or "MMC Site") means any
     World Wide Web server that publishes copyrightable works and also
     provides prominent facilities for anybody to edit those works.  A
     public wiki that anybody can edit is an example of such a server.
     A "Massive Multiauthor Collaboration" (or "MMC") contained in the
     site means any set of copyrightable works thus published on the MMC
     site.

     "CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
     license published by Creative Commons Corporation, a not-for-profit
     corporation with a principal place of business in San Francisco,
     California, as well as future copyleft versions of that license
     published by that same organization.

     "Incorporate" means to publish or republish a Document, in whole or
     in part, as part of another Document.

     An MMC is "eligible for relicensing" if it is licensed under this
     License, and if all works that were first published under this
     License somewhere other than this MMC, and subsequently
     incorporated in whole or in part into the MMC, (1) had no cover
     texts or invariant sections, and (2) were thus incorporated prior
     to November 1, 2008.

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       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
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File: coreutils.info,  Node: Concept index,  Prev: GNU Free Documentation License,  Up: Top

Index
*****

[index]
* Menu:

* !:                                     Connectives for test.
                                                              (line   9)
* !=:                                    String tests.        (line  25)
* %:                                     Numeric expressions. (line  16)
* %b:                                    printf invocation.   (line  38)
* &:                                     Relations for expr.  (line  17)
* *:                                     Numeric expressions. (line  16)
* + <1>:                                 Numeric expressions. (line  12)
* +:                                     String expressions.  (line  53)
* +PAGE_RANGE:                           pr invocation.       (line  58)
* - <1>:                                 su invocation.       (line  57)
* - <2>:                                 env invocation.      (line  96)
* -:                                     Numeric expressions. (line  12)
* - and Unix rm:                         rm invocation.       (line 110)
* -, removing files beginning with:      rm invocation.       (line  98)
* --:                                    Common options.      (line  44)
* --across:                              pr invocation.       (line  82)
* --address-radix:                       od invocation.       (line  36)
* --adjustment:                          nice invocation.     (line  47)
* --all <1>:                             uname invocation.    (line  30)
* --all <2>:                             nproc invocation.    (line  19)
* --all <3>:                             who invocation.      (line  36)
* --all <4>:                             stty invocation.     (line  26)
* --all <5>:                             du invocation.       (line  26)
* --all <6>:                             df invocation.       (line  32)
* --all <7>:                             Which files are listed.
                                                              (line  13)
* --all:                                 unexpand invocation. (line  37)
* --all-repeated:                        uniq invocation.     (line  69)
* --almost-all:                          Which files are listed.
                                                              (line  17)
* --apparent-size:                       du invocation.       (line  29)
* --append:                              tee invocation.      (line  25)
* --archive:                             cp invocation.       (line  65)
* --author:                              What information is listed.
                                                              (line  10)
* --backup <1>:                          ln invocation.       (line  84)
* --backup <2>:                          mv invocation.       (line  56)
* --backup <3>:                          install invocation.  (line  42)
* --backup <4>:                          cp invocation.       (line  75)
* --backup:                              Backup options.      (line  13)
* --batch-size:                          sort invocation.     (line 250)
* --before:                              tac invocation.      (line  21)
* --binary:                              md5sum invocation.   (line  38)
* --block-size <1>:                      du invocation.       (line  50)
* --block-size <2>:                      df invocation.       (line  38)
* --block-size:                          Block size.          (line 138)
* --block-size=SIZE:                     Block size.          (line  12)
* --body-numbering:                      nl invocation.       (line  47)
* --boot:                                who invocation.      (line  40)
* --bourne-shell:                        dircolors invocation.
                                                              (line  34)
* --buffer-size:                         sort invocation.     (line 300)
* --bytes <1>:                           du invocation.       (line  46)
* --bytes <2>:                           cut invocation.      (line  26)
* --bytes <3>:                           wc invocation.       (line  43)
* --bytes <4>:                           split invocation.    (line  33)
* --bytes <5>:                           tail invocation.     (line  32)
* --bytes <6>:                           head invocation.     (line  24)
* --bytes:                               fold invocation.     (line  23)
* --c-shell:                             dircolors invocation.
                                                              (line  40)
* --canonicalize:                        readlink invocation. (line  29)
* --canonicalize-existing:               readlink invocation. (line  36)
* --canonicalize-missing:                readlink invocation. (line  43)
* --changes <1>:                         chmod invocation.    (line  39)
* --changes <2>:                         chgrp invocation.    (line  20)
* --changes:                             chown invocation.    (line  70)
* --characters:                          cut invocation.      (line  34)
* --chars:                               wc invocation.       (line  47)
* --check:                               sort invocation.     (line  18)
* --check-chars:                         uniq invocation.     (line 106)
* --classify:                            General output formatting.
                                                              (line  36)
* --color:                               General output formatting.
                                                              (line  21)
* --columns:                             pr invocation.       (line  68)
* --command:                             su invocation.       (line  43)
* --compare:                             install invocation.  (line  47)
* --complement:                          cut invocation.      (line  71)
* --compute:                             runcon invocation.   (line  27)
* --context <1>:                         id invocation.       (line  48)
* --context <2>:                         mknod invocation.    (line  57)
* --context <3>:                         mkfifo invocation.   (line  30)
* --context <4>:                         mkdir invocation.    (line  65)
* --context <5>:                         install invocation.  (line 133)
* --context:                             What information is listed.
                                                              (line 268)
* --count <1>:                           who invocation.      (line  70)
* --count:                               uniq invocation.     (line  55)
* --count-links:                         du invocation.       (line  96)
* --crown-margin:                        fmt invocation.      (line  34)
* --csh:                                 dircolors invocation.
                                                              (line  40)
* --date <1>:                            Options for date.    (line  11)
* --date:                                touch invocation.    (line  61)
* --dead:                                who invocation.      (line  44)
* --decode:                              base64 invocation.   (line  30)
* --delimiter:                           cut invocation.      (line  51)
* --delimiters:                          paste invocation.    (line  43)
* --dereference <1>:                     stat invocation.     (line  22)
* --dereference <2>:                     du invocation.       (line 101)
* --dereference <3>:                     chgrp invocation.    (line  30)
* --dereference <4>:                     chown invocation.    (line 103)
* --dereference <5>:                     cp invocation.       (line 148)
* --dereference:                         Which files are listed.
                                                              (line  84)
* --dereference-args:                    du invocation.       (line  61)
* --dereference-command-line:            Which files are listed.
                                                              (line  36)
* --dereference-command-line-symlink-to-dir: Which files are listed.
                                                              (line  41)
* --dictionary-order:                    sort invocation.     (line  87)
* --digits:                              csplit invocation.   (line  80)
* --direct:                              df invocation.       (line  42)
* --directory <1>:                       mktemp invocation.   (line  86)
* --directory <2>:                       ln invocation.       (line  90)
* --directory <3>:                       install invocation.  (line  62)
* --directory:                           Which files are listed.
                                                              (line  28)
* --dired:                               What information is listed.
                                                              (line  16)
* --double-space:                        pr invocation.       (line  94)
* --dry-run:                             mktemp invocation.   (line  98)
* --echo:                                shuf invocation.     (line  19)
* --elide-empty-files:                   csplit invocation.   (line  89)
* --error:                               stdbuf invocation.   (line  27)
* --escape:                              Formatting the file names.
                                                              (line  11)
* --exact:                               shred invocation.    (line 134)
* --exclude-from=FILE:                   du invocation.       (line 211)
* --exclude-type:                        df invocation.       (line 149)
* --exclude=PATTERN:                     du invocation.       (line 205)
* --expand-tabs:                         pr invocation.       (line 118)
* --fast:                                su invocation.       (line  48)
* --field-separator:                     sort invocation.     (line 316)
* --fields:                              cut invocation.      (line  44)
* --file <1>:                            Options for date.    (line  26)
* --file:                                stty invocation.     (line  31)
* --file-system:                         stat invocation.     (line  28)
* --file-type:                           General output formatting.
                                                              (line  47)
* --files0-from=FILE <1>:                du invocation.       (line  67)
* --files0-from=FILE <2>:                sort invocation.     (line 218)
* --files0-from=FILE:                    wc invocation.       (line  62)
* --first-line-number:                   pr invocation.       (line 194)
* --follow:                              tail invocation.     (line  48)
* --footer-numbering:                    nl invocation.       (line  75)
* --force <1>:                           ln invocation.       (line  96)
* --force <2>:                           shred invocation.    (line 101)
* --force <3>:                           rm invocation.       (line  35)
* --force <4>:                           mv invocation.       (line  61)
* --force:                               cp invocation.       (line 115)
* --form-feed:                           pr invocation.       (line 126)
* --format <1>:                          General output formatting.
                                                              (line  10)
* --format <2>:                          What information is listed.
                                                              (line 131)
* --format:                              od invocation.       (line  85)
* --format=FORMAT <1>:                   seq invocation.      (line  24)
* --format=FORMAT:                       stat invocation.     (line  33)
* --from:                                chown invocation.    (line  80)
* --full-time:                           What information is listed.
                                                              (line 100)
* --general-numeric-sort:                sort invocation.     (line 105)
* --group <1>:                           id invocation.       (line  26)
* --group:                               install invocation.  (line  68)
* --group-directories-first:             Which files are listed.
                                                              (line  50)
* --groups <1>:                          chroot invocation.   (line  29)
* --groups:                              id invocation.       (line  30)
* --hardware-platform:                   uname invocation.    (line  35)
* --head-count:                          shuf invocation.     (line  32)
* --header:                              pr invocation.       (line 131)
* --header-numbering:                    nl invocation.       (line  79)
* --heading:                             who invocation.      (line  48)
* --help:                                Common options.      (line  37)
* --hide-control-chars:                  Formatting the file names.
                                                              (line  23)
* --hide=PATTERN:                        Which files are listed.
                                                              (line  57)
* --human-numeric-sort:                  sort invocation.     (line 133)
* --human-readable <1>:                  du invocation.       (line  81)
* --human-readable <2>:                  df invocation.       (line  53)
* --human-readable <3>:                  What information is listed.
                                                              (line 116)
* --human-readable:                      Block size.          (line 138)
* --ignore:                              nproc invocation.    (line  25)
* --ignore-backups:                      Which files are listed.
                                                              (line  23)
* --ignore-case <1>:                     join invocation.     (line  89)
* --ignore-case <2>:                     uniq invocation.     (line  59)
* --ignore-case:                         sort invocation.     (line  94)
* --ignore-environment:                  env invocation.      (line  96)
* --ignore-fail-on-non-empty:            rmdir invocation.    (line  17)
* --ignore-garbage:                      base64 invocation.   (line  36)
* --ignore-interrupts:                   tee invocation.      (line  30)
* --ignore-leading-blanks:               sort invocation.     (line  79)
* --ignore-nonprinting:                  sort invocation.     (line 142)
* --ignore=PATTERN:                      Which files are listed.
                                                              (line  70)
* --indent:                              pr invocation.       (line 200)
* --indicator-style:                     General output formatting.
                                                              (line  36)
* --initial:                             expand invocation.   (line  34)
* --inode:                               What information is listed.
                                                              (line 123)
* --inodes:                              df invocation.       (line  63)
* --input:                               stdbuf invocation.   (line  19)
* --input-range:                         shuf invocation.     (line  23)
* --interactive <1>:                     ln invocation.       (line 100)
* --interactive <2>:                     rm invocation.       (line  50)
* --interactive <3>:                     mv invocation.       (line  67)
* --interactive:                         cp invocation.       (line 138)
* --io-blocks:                           truncate invocation. (line  26)
* --iterations=NUMBER:                   shred invocation.    (line 106)
* --join-blank-lines:                    nl invocation.       (line  87)
* --join-lines:                          pr invocation.       (line 144)
* --keep-files:                          csplit invocation.   (line  85)
* --kernel-name:                         uname invocation.    (line  65)
* --kernel-release:                      uname invocation.    (line  61)
* --kernel-version:                      uname invocation.    (line  76)
* --key:                                 sort invocation.     (line 231)
* --length:                              pr invocation.       (line 153)
* --line-bytes:                          split invocation.    (line  47)
* --line-increment:                      nl invocation.       (line  83)
* --lines <1>:                           wc invocation.       (line  55)
* --lines <2>:                           split invocation.    (line  26)
* --lines <3>:                           tail invocation.     (line 153)
* --lines:                               head invocation.     (line  39)
* --link:                                cp invocation.       (line 144)
* --literal:                             Formatting the file names.
                                                              (line  17)
* --local:                               df invocation.       (line  74)
* --logical <1>:                         pwd invocation.      (line  15)
* --logical:                             ln invocation.       (line 104)
* --login <1>:                           su invocation.       (line  57)
* --login:                               who invocation.      (line  52)
* --lookup:                              who invocation.      (line  57)
* --machine:                             uname invocation.    (line  41)
* --max-depth=DEPTH:                     du invocation.       (line 116)
* --max-line-length:                     wc invocation.       (line  59)
* --max-unchanged-stats:                 tail invocation.     (line 141)
* --merge <1>:                           sort invocation.     (line  32)
* --merge:                               pr invocation.       (line 160)
* --mesg:                                who invocation.      (line  95)
* --message:                             who invocation.      (line  95)
* --mode <1>:                            mknod invocation.    (line  48)
* --mode <2>:                            mkfifo invocation.   (line  21)
* --mode <3>:                            mkdir invocation.    (line  19)
* --mode:                                install invocation.  (line  74)
* --month-sort:                          sort invocation.     (line 149)
* --name:                                id invocation.       (line  34)
* --no-clobber <1>:                      mv invocation.       (line  74)
* --no-clobber:                          cp invocation.       (line 155)
* --no-create <1>:                       truncate invocation. (line  22)
* --no-create:                           touch invocation.    (line  57)
* --no-dereference <1>:                  chcon invocation.    (line  22)
* --no-dereference <2>:                  du invocation.       (line 112)
* --no-dereference <3>:                  touch invocation.    (line  75)
* --no-dereference <4>:                  chgrp invocation.    (line  35)
* --no-dereference <5>:                  chown invocation.    (line 108)
* --no-dereference <6>:                  ln invocation.       (line 110)
* --no-dereference:                      cp invocation.       (line 161)
* --no-file-warnings:                    pr invocation.       (line 207)
* --no-group:                            What information is listed.
                                                              (line 110)
* --no-newline:                          readlink invocation. (line  48)
* --no-preserve-root <1>:                chmod invocation.    (line  54)
* --no-preserve-root <2>:                chgrp invocation.    (line  48)
* --no-preserve-root <3>:                chown invocation.    (line 121)
* --no-preserve-root:                    rm invocation.       (line  84)
* --no-renumber:                         nl invocation.       (line 108)
* --no-sync:                             df invocation.       (line  78)
* --no-target-directory <1>:             ln invocation.       (line 153)
* --no-target-directory <2>:             mv invocation.       (line 107)
* --no-target-directory <3>:             install invocation.  (line 124)
* --no-target-directory <4>:             cp invocation.       (line 345)
* --no-target-directory:                 Target directory.    (line  15)
* --nodename:                            uname invocation.    (line  46)
* --null <1>:                            env invocation.      (line  83)
* --null <2>:                            printenv invocation. (line  19)
* --null:                                du invocation.       (line 122)
* --number:                              cat invocation.      (line  31)
* --number-format:                       nl invocation.       (line  95)
* --number-lines:                        pr invocation.       (line 173)
* --number-nonblank:                     cat invocation.      (line  20)
* --number-separator:                    nl invocation.       (line 112)
* --number-width:                        nl invocation.       (line 122)
* --numeric-sort:                        sort invocation.     (line 159)
* --numeric-suffixes:                    split invocation.    (line  58)
* --numeric-uid-gid:                     What information is listed.
                                                              (line 234)
* --omit-header:                         pr invocation.       (line 231)
* --omit-pagination:                     pr invocation.       (line 242)
* --one-file-system <1>:                 du invocation.       (line 201)
* --one-file-system <2>:                 rm invocation.       (line  63)
* --one-file-system:                     cp invocation.       (line 364)
* --only-delimited:                      cut invocation.      (line  59)
* --operating-system:                    uname invocation.    (line  57)
* --output <1>:                          stdbuf invocation.   (line  23)
* --output <2>:                          shuf invocation.     (line  37)
* --output:                              sort invocation.     (line 276)
* --output-delimiter:                    cut invocation.      (line  64)
* --output-duplicates:                   od invocation.       (line 155)
* --output-tabs:                         pr invocation.       (line 137)
* --owner:                               install invocation.  (line  86)
* --page_width:                          pr invocation.       (line 260)
* --pages=PAGE_RANGE:                    pr invocation.       (line  58)
* --parents <1>:                         rmdir invocation.    (line  22)
* --parents <2>:                         mkdir invocation.    (line  39)
* --parents:                             cp invocation.       (line 240)
* --physical <1>:                        pwd invocation.      (line  22)
* --physical:                            ln invocation.       (line 129)
* --pid:                                 tail invocation.     (line 121)
* --portability <1>:                     pathchk invocation.  (line  46)
* --portability:                         df invocation.       (line  85)
* --prefix:                              csplit invocation.   (line  62)
* --preserve:                            cp invocation.       (line 168)
* --preserve-context:                    install invocation.  (line  91)
* --preserve-environment:                su invocation.       (line  69)
* --preserve-root <1>:                   chmod invocation.    (line  49)
* --preserve-root <2>:                   chgrp invocation.    (line  43)
* --preserve-root <3>:                   chown invocation.    (line 116)
* --preserve-root:                       rm invocation.       (line  79)
* --preserve-timestamps:                 install invocation.  (line  98)
* --print-database:                      dircolors invocation.
                                                              (line  45)
* --print-type:                          df invocation.       (line 124)
* --printf=FORMAT:                       stat invocation.     (line  42)
* --process:                             who invocation.      (line  66)
* --processor:                           uname invocation.    (line  50)
* --quiet <1>:                           tty invocation.      (line  18)
* --quiet <2>:                           mktemp invocation.   (line  93)
* --quiet <3>:                           chmod invocation.    (line  45)
* --quiet <4>:                           chgrp invocation.    (line  26)
* --quiet <5>:                           chown invocation.    (line  76)
* --quiet <6>:                           readlink invocation. (line  54)
* --quiet <7>:                           md5sum invocation.   (line  69)
* --quiet <8>:                           csplit invocation.   (line 100)
* --quiet <9>:                           tail invocation.     (line 161)
* --quiet:                               head invocation.     (line  46)
* --quote-name:                          Formatting the file names.
                                                              (line  30)
* --quoting-style:                       Formatting the file names.
                                                              (line  11)
* --random-sort:                         sort invocation.     (line 188)
* --random-source <1>:                   shred invocation.    (line 112)
* --random-source <2>:                   shuf invocation.     (line  43)
* --random-source:                       sort invocation.     (line 289)
* --range <1>:                           runcon invocation.   (line  43)
* --range:                               chcon invocation.    (line  63)
* --read-bytes:                          od invocation.       (line  71)
* --real:                                id invocation.       (line  39)
* --recursive <1>:                       chcon invocation.    (line  30)
* --recursive <2>:                       chmod invocation.    (line  69)
* --recursive <3>:                       chgrp invocation.    (line  66)
* --recursive <4>:                       chown invocation.    (line 140)
* --recursive <5>:                       rm invocation.       (line  91)
* --recursive <6>:                       cp invocation.       (line 253)
* --recursive:                           Which files are listed.
                                                              (line  91)
* --reference <1>:                       chcon invocation.    (line  25)
* --reference <2>:                       Options for date.    (line  34)
* --reference <3>:                       truncate invocation. (line  30)
* --reference <4>:                       touch invocation.    (line  94)
* --reference <5>:                       chmod invocation.    (line  62)
* --reference <6>:                       chgrp invocation.    (line  52)
* --reference:                           chown invocation.    (line 125)
* --reflink[=WHEN]:                      cp invocation.       (line 266)
* --regex:                               tac invocation.      (line  26)
* --remove:                              shred invocation.    (line 123)
* --remove-destination:                  cp invocation.       (line 285)
* --repeated:                            uniq invocation.     (line  63)
* --retry:                               tail invocation.     (line 104)
* --reverse <1>:                         Sorting the output.  (line  27)
* --reverse:                             sort invocation.     (line 182)
* --rfc-2822:                            Options for date.    (line  40)
* --rfc-3339=TIMESPEC:                   Options for date.    (line  52)
* --rfc-822:                             Options for date.    (line  40)
* --role <1>:                            runcon invocation.   (line  35)
* --role:                                chcon invocation.    (line  55)
* --runlevel:                            who invocation.      (line  75)
* --save:                                stty invocation.     (line  41)
* --section-delimiter:                   nl invocation.       (line  68)
* --sep-string:                          pr invocation.       (line 221)
* --separate-dirs:                       du invocation.       (line 140)
* --separator <1>:                       pr invocation.       (line 212)
* --separator:                           tac invocation.      (line  33)
* --serial:                              paste invocation.    (line  34)
* --set:                                 Options for date.    (line  82)
* --sh:                                  dircolors invocation.
                                                              (line  34)
* --shell:                               su invocation.       (line  80)
* --show-all:                            cat invocation.      (line  16)
* --show-control-chars <1>:              Formatting the file names.
                                                              (line  78)
* --show-control-chars:                  pr invocation.       (line  88)
* --show-ends:                           cat invocation.      (line  27)
* --show-nonprinting <1>:                pr invocation.       (line 247)
* --show-nonprinting:                    cat invocation.      (line  50)
* --show-tabs:                           cat invocation.      (line  43)
* --si <1>:                              du invocation.       (line 128)
* --si <2>:                              df invocation.       (line 104)
* --si <3>:                              What information is listed.
                                                              (line 260)
* --si:                                  Block size.          (line 138)
* --signal:                              timeout invocation.  (line  34)
* --silent <1>:                          tty invocation.      (line  18)
* --silent <2>:                          chmod invocation.    (line  45)
* --silent <3>:                          chgrp invocation.    (line  26)
* --silent <4>:                          chown invocation.    (line  76)
* --silent <5>:                          readlink invocation. (line  54)
* --silent <6>:                          csplit invocation.   (line 100)
* --silent <7>:                          tail invocation.     (line 161)
* --silent:                              head invocation.     (line  46)
* --size <1>:                            truncate invocation. (line  34)
* --size:                                What information is listed.
                                                              (line 244)
* --size=BYTES:                          shred invocation.    (line 117)
* --skip-bytes:                          od invocation.       (line  55)
* --skip-chars:                          uniq invocation.     (line  41)
* --skip-fields:                         uniq invocation.     (line  31)
* --sleep-interval:                      tail invocation.     (line 110)
* --sort <1>:                            Sorting the output.  (line  32)
* --sort:                                sort invocation.     (line 105)
* --spaces:                              fold invocation.     (line  29)
* --sparse=WHEN:                         cp invocation.       (line 289)
* --split-only:                          fmt invocation.      (line  47)
* --squeeze-blank:                       cat invocation.      (line  35)
* --stable:                              sort invocation.     (line 294)
* --starting-line-number:                nl invocation.       (line 117)
* --status:                              md5sum invocation.   (line  77)
* --strings:                             od invocation.       (line  76)
* --strip:                               install invocation.  (line 108)
* --strip-program:                       install invocation.  (line 111)
* --strip-trailing-slashes <1>:          mv invocation.       (line  93)
* --strip-trailing-slashes:              cp invocation.       (line 323)
* --suffix <1>:                          mktemp invocation.   (line 114)
* --suffix <2>:                          ln invocation.       (line 144)
* --suffix <3>:                          mv invocation.       (line  98)
* --suffix <4>:                          install invocation.  (line 115)
* --suffix <5>:                          cp invocation.       (line 336)
* --suffix <6>:                          csplit invocation.   (line  66)
* --suffix:                              Backup options.      (line  50)
* --suffix-length:                       split invocation.    (line  54)
* --summarize:                           du invocation.       (line 136)
* --symbolic:                            ln invocation.       (line 138)
* --symbolic-link:                       cp invocation.       (line 328)
* --sync:                                df invocation.       (line 111)
* --sysv:                                sum invocation.      (line  31)
* --tabs <1>:                            unexpand invocation. (line  24)
* --tabs:                                expand invocation.   (line  22)
* --tabsize:                             General output formatting.
                                                              (line  92)
* --tagged-paragraph:                    fmt invocation.      (line  40)
* --target-directory <1>:                ln invocation.       (line 149)
* --target-directory <2>:                mv invocation.       (line 103)
* --target-directory <3>:                install invocation.  (line 120)
* --target-directory <4>:                cp invocation.       (line 341)
* --target-directory:                    Target directory.    (line  31)
* --temporary-directory:                 sort invocation.     (line 336)
* --terse:                               stat invocation.     (line  53)
* --text:                                md5sum invocation.   (line  87)
* --time <1>:                            who invocation.      (line  83)
* --time <2>:                            du invocation.       (line 148)
* --time <3>:                            touch invocation.    (line  53)
* --time:                                Sorting the output.  (line  13)
* --time-style <1>:                      du invocation.       (line 163)
* --time-style:                          Formatting file timestamps.
                                                              (line  26)
* --tmpdir:                              mktemp invocation.   (line 106)
* --total <1>:                           du invocation.       (line  55)
* --total:                               df invocation.       (line  47)
* --traditional:                         od invocation.       (line 206)
* --type <1>:                            runcon invocation.   (line  39)
* --type <2>:                            chcon invocation.    (line  59)
* --type:                                df invocation.       (line 118)
* --uniform-spacing:                     fmt invocation.      (line  53)
* --unique <1>:                          uniq invocation.     (line 101)
* --unique:                              sort invocation.     (line 345)
* --universal:                           Options for date.    (line  87)
* --unset:                               env invocation.      (line  90)
* --update <1>:                          mv invocation.       (line  80)
* --update:                              cp invocation.       (line 350)
* --user <1>:                            runcon invocation.   (line  31)
* --user <2>:                            chcon invocation.    (line  51)
* --user:                                id invocation.       (line  44)
* --userspec:                            chroot invocation.   (line  24)
* --utc:                                 Options for date.    (line  87)
* --verbose <1>:                         chcon invocation.    (line  47)
* --verbose <2>:                         chmod invocation.    (line  59)
* --verbose <3>:                         chgrp invocation.    (line  58)
* --verbose <4>:                         chown invocation.    (line 132)
* --verbose <5>:                         rmdir invocation.    (line  31)
* --verbose <6>:                         readlink invocation. (line  58)
* --verbose <7>:                         mkdir invocation.    (line  60)
* --verbose <8>:                         ln invocation.       (line 158)
* --verbose <9>:                         shred invocation.    (line 129)
* --verbose <10>:                        rm invocation.       (line  95)
* --verbose <11>:                        mv invocation.       (line  90)
* --verbose <12>:                        install invocation.  (line 129)
* --verbose <13>:                        cp invocation.       (line 360)
* --verbose <14>:                        split invocation.    (line  61)
* --verbose <15>:                        tail invocation.     (line 165)
* --verbose:                             head invocation.     (line  50)
* --version:                             Common options.      (line  41)
* --version-sort:                        sort invocation.     (line 176)
* --warn:                                md5sum invocation.   (line  96)
* --width <1>:                           General output formatting.
                                                              (line 104)
* --width <2>:                           fold invocation.     (line  35)
* --width <3>:                           pr invocation.       (line 251)
* --width <4>:                           fmt invocation.      (line  59)
* --width:                               od invocation.       (line 162)
* --words:                               wc invocation.       (line  51)
* --wrap:                                base64 invocation.   (line  22)
* --writable:                            who invocation.      (line  95)
* --zero:                                shred invocation.    (line 144)
* --zero-terminated <1>:                 uniq invocation.     (line 112)
* --zero-terminated <2>:                 shuf invocation.     (line  48)
* --zero-terminated:                     sort invocation.     (line 359)
* -0 <1>:                                env invocation.      (line  82)
* -0 <2>:                                printenv invocation. (line  18)
* -0:                                    du invocation.       (line 121)
* -1 <1>:                                General output formatting.
                                                              (line  10)
* -1 <2>:                                join invocation.     (line  94)
* -1:                                    comm invocation.     (line  23)
* -2 <1>:                                join invocation.     (line  97)
* -2:                                    comm invocation.     (line  23)
* -3:                                    comm invocation.     (line  23)
* -a <1>:                                uname invocation.    (line  30)
* -a <2>:                                who invocation.      (line  36)
* -a <3>:                                stty invocation.     (line  26)
* -a <4>:                                tee invocation.      (line  25)
* -a <5>:                                Connectives for test.
                                                              (line  12)
* -a <6>:                                du invocation.       (line  26)
* -a <7>:                                df invocation.       (line  32)
* -a <8>:                                touch invocation.    (line  53)
* -a:                                    cp invocation.       (line  65)
* -A:                                    Which files are listed.
                                                              (line  17)
* -a <1>:                                Which files are listed.
                                                              (line  13)
* -a <2>:                                unexpand invocation. (line  37)
* -a <3>:                                join invocation.     (line  73)
* -a <4>:                                split invocation.    (line  54)
* -a <5>:                                pr invocation.       (line  82)
* -a:                                    od invocation.       (line 175)
* -A <1>:                                od invocation.       (line  36)
* -A:                                    cat invocation.      (line  16)
* -b <1>:                                who invocation.      (line  40)
* -b:                                    File type tests.     (line  10)
* -B:                                    du invocation.       (line  50)
* -b:                                    du invocation.       (line  46)
* -B:                                    df invocation.       (line  38)
* -b <1>:                                ln invocation.       (line  84)
* -b <2>:                                mv invocation.       (line  56)
* -b <3>:                                install invocation.  (line  42)
* -b <4>:                                cp invocation.       (line  75)
* -b <5>:                                dircolors invocation.
                                                              (line  34)
* -b:                                    Formatting the file names.
                                                              (line  11)
* -B:                                    Which files are listed.
                                                              (line  23)
* -b <1>:                                cut invocation.      (line  26)
* -b <2>:                                sort invocation.     (line  79)
* -b <3>:                                md5sum invocation.   (line  38)
* -b <4>:                                csplit invocation.   (line  66)
* -b <5>:                                split invocation.    (line  33)
* -b <6>:                                fold invocation.     (line  23)
* -b <7>:                                od invocation.       (line 178)
* -b <8>:                                nl invocation.       (line  47)
* -b <9>:                                tac invocation.      (line  21)
* -b <10>:                               cat invocation.      (line  20)
* -b:                                    Backup options.      (line  13)
* -c <1>:                                su invocation.       (line  43)
* -c <2>:                                runcon invocation.   (line  27)
* -c <3>:                                File type tests.     (line  13)
* -c <4>:                                truncate invocation. (line  22)
* -c <5>:                                stat invocation.     (line  33)
* -c <6>:                                du invocation.       (line  55)
* -c <7>:                                touch invocation.    (line  57)
* -c <8>:                                chmod invocation.    (line  39)
* -c <9>:                                chgrp invocation.    (line  20)
* -c <10>:                               chown invocation.    (line  70)
* -c:                                    install invocation.  (line  53)
* -C:                                    install invocation.  (line  47)
* -c:                                    dircolors invocation.
                                                              (line  40)
* -C:                                    General output formatting.
                                                              (line  15)
* -c <1>:                                Sorting the output.  (line  13)
* -c <2>:                                cut invocation.      (line  34)
* -c <3>:                                uniq invocation.     (line  55)
* -c <4>:                                shuf invocation.     (line  19)
* -c <5>:                                sort invocation.     (line  18)
* -c:                                    wc invocation.       (line  43)
* -C:                                    split invocation.    (line  47)
* -c <1>:                                tail invocation.     (line  32)
* -c <2>:                                head invocation.     (line  24)
* -c <3>:                                pr invocation.       (line  88)
* -c <4>:                                fmt invocation.      (line  34)
* -c:                                    od invocation.       (line 181)
* -COLUMN:                               pr invocation.       (line  68)
* -d <1>:                                Options for date.    (line  11)
* -d <2>:                                who invocation.      (line  44)
* -d <3>:                                mktemp invocation.   (line  86)
* -d:                                    File type tests.     (line  16)
* -D:                                    du invocation.       (line  61)
* -d <1>:                                touch invocation.    (line  61)
* -d <2>:                                ln invocation.       (line  90)
* -d:                                    install invocation.  (line  62)
* -D:                                    install invocation.  (line  56)
* -d:                                    cp invocation.       (line 108)
* -D:                                    What information is listed.
                                                              (line  16)
* -d <1>:                                Which files are listed.
                                                              (line  28)
* -d <2>:                                paste invocation.    (line  43)
* -d:                                    cut invocation.      (line  51)
* -D:                                    uniq invocation.     (line  69)
* -d <1>:                                uniq invocation.     (line  63)
* -d <2>:                                sort invocation.     (line  87)
* -d <3>:                                split invocation.    (line  58)
* -d <4>:                                pr invocation.       (line  94)
* -d <5>:                                base64 invocation.   (line  30)
* -d <6>:                                od invocation.       (line 185)
* -d:                                    nl invocation.       (line  68)
* -e <1>:                                stdbuf invocation.   (line  27)
* -e:                                    File characteristic tests.
                                                              (line   9)
* -E:                                    echo invocation.     (line  73)
* -e <1>:                                echo invocation.     (line  25)
* -e <2>:                                readlink invocation. (line  36)
* -e <3>:                                join invocation.     (line  84)
* -e:                                    pr invocation.       (line 118)
* -E:                                    cat invocation.      (line  27)
* -e:                                    cat invocation.      (line  23)
* -ef:                                   File characteristic tests.
                                                              (line  23)
* -eq:                                   Numeric tests.       (line  16)
* -f <1>:                                su invocation.       (line  48)
* -f:                                    Options for date.    (line  26)
* -F:                                    stty invocation.     (line  31)
* -f <1>:                                File type tests.     (line  19)
* -f <2>:                                stat invocation.     (line  28)
* -f <3>:                                touch invocation.    (line  71)
* -f <4>:                                chmod invocation.    (line  45)
* -f <5>:                                chgrp invocation.    (line  26)
* -f <6>:                                chown invocation.    (line  76)
* -f <7>:                                readlink invocation. (line  29)
* -f:                                    ln invocation.       (line  96)
* -F:                                    ln invocation.       (line  90)
* -f <1>:                                shred invocation.    (line 101)
* -f <2>:                                rm invocation.       (line  35)
* -f <3>:                                mv invocation.       (line  61)
* -f:                                    cp invocation.       (line 115)
* -F:                                    General output formatting.
                                                              (line  36)
* -f <1>:                                Sorting the output.  (line  20)
* -f <2>:                                cut invocation.      (line  44)
* -f <3>:                                uniq invocation.     (line  31)
* -f <4>:                                sort invocation.     (line  94)
* -f:                                    csplit invocation.   (line  62)
* -F:                                    tail invocation.     (line  99)
* -f <1>:                                tail invocation.     (line  48)
* -f:                                    pr invocation.       (line 126)
* -F:                                    pr invocation.       (line 126)
* -f <1>:                                od invocation.       (line 188)
* -f:                                    nl invocation.       (line  75)
* -f FORMAT:                             seq invocation.      (line  24)
* -G:                                    id invocation.       (line  30)
* -g <1>:                                id invocation.       (line  26)
* -g:                                    stty invocation.     (line  41)
* -G:                                    Access permission tests.
                                                              (line  31)
* -g <1>:                                Access permission tests.
                                                              (line   9)
* -g:                                    install invocation.  (line  68)
* -G:                                    What information is listed.
                                                              (line 110)
* -g <1>:                                What information is listed.
                                                              (line 105)
* -g:                                    sort invocation.     (line 105)
* -ge:                                   Numeric tests.       (line  16)
* -gt:                                   Numeric tests.       (line  16)
* -H:                                    chcon invocation.    (line  33)
* -h:                                    chcon invocation.    (line  22)
* -H:                                    who invocation.      (line  48)
* -h:                                    File type tests.     (line  23)
* -H:                                    du invocation.       (line  87)
* -h:                                    du invocation.       (line  81)
* -H:                                    df invocation.       (line  59)
* -h <1>:                                df invocation.       (line  53)
* -h:                                    touch invocation.    (line  75)
* -H:                                    chgrp invocation.    (line  70)
* -h:                                    chgrp invocation.    (line  35)
* -H:                                    chown invocation.    (line 143)
* -h:                                    chown invocation.    (line 108)
* -H:                                    cp invocation.       (line 131)
* -h:                                    What information is listed.
                                                              (line 116)
* -H:                                    Which files are listed.
                                                              (line  36)
* -h <1>:                                sort invocation.     (line 133)
* -h <2>:                                pr invocation.       (line 131)
* -h:                                    nl invocation.       (line  79)
* -H:                                    Traversing symlinks. (line  18)
* -h:                                    Block size.          (line 138)
* -i <1>:                                stdbuf invocation.   (line  19)
* -i <2>:                                env invocation.      (line  96)
* -i <3>:                                uname invocation.    (line  35)
* -i <4>:                                tee invocation.      (line  30)
* -i <5>:                                df invocation.       (line  63)
* -i:                                    ln invocation.       (line 100)
* -I:                                    rm invocation.       (line  44)
* -i <1>:                                rm invocation.       (line  39)
* -i <2>:                                mv invocation.       (line  67)
* -i <3>:                                cp invocation.       (line 138)
* -i:                                    What information is listed.
                                                              (line 123)
* -I:                                    Which files are listed.
                                                              (line  70)
* -i <1>:                                expand invocation.   (line  34)
* -i <2>:                                join invocation.     (line  89)
* -i <3>:                                uniq invocation.     (line  59)
* -i <4>:                                shuf invocation.     (line  23)
* -i <5>:                                sort invocation.     (line 142)
* -i <6>:                                pr invocation.       (line 137)
* -i <7>:                                base64 invocation.   (line  36)
* -i <8>:                                od invocation.       (line 191)
* -i:                                    nl invocation.       (line  83)
* -J:                                    pr invocation.       (line 144)
* -j:                                    od invocation.       (line  55)
* -k <1>:                                Access permission tests.
                                                              (line  12)
* -k <2>:                                du invocation.       (line  90)
* -k <3>:                                df invocation.       (line  68)
* -k <4>:                                General output formatting.
                                                              (line  72)
* -k <5>:                                sort invocation.     (line 231)
* -k <6>:                                csplit invocation.   (line  85)
* -k:                                    Block size.          (line 138)
* -l <1>:                                su invocation.       (line  57)
* -l <2>:                                runcon invocation.   (line  43)
* -l:                                    chcon invocation.    (line  63)
* -L:                                    chcon invocation.    (line  38)
* -l:                                    who invocation.      (line  52)
* -L <1>:                                pwd invocation.      (line  15)
* -L <2>:                                File type tests.     (line  23)
* -L <3>:                                stat invocation.     (line  22)
* -L:                                    du invocation.       (line 101)
* -l <1>:                                du invocation.       (line  96)
* -l:                                    df invocation.       (line  74)
* -L <1>:                                chgrp invocation.    (line  75)
* -L <2>:                                chown invocation.    (line 148)
* -L <3>:                                ln invocation.       (line 104)
* -L:                                    cp invocation.       (line 148)
* -l <1>:                                cp invocation.       (line 144)
* -l:                                    What information is listed.
                                                              (line 131)
* -L <1>:                                Which files are listed.
                                                              (line  84)
* -L:                                    wc invocation.       (line  59)
* -l <1>:                                wc invocation.       (line  55)
* -l <2>:                                split invocation.    (line  26)
* -l <3>:                                pr invocation.       (line 153)
* -l <4>:                                od invocation.       (line 194)
* -l:                                    nl invocation.       (line  87)
* -L:                                    Traversing symlinks. (line  22)
* -le:                                   Numeric tests.       (line  16)
* -lt:                                   Numeric tests.       (line  16)
* -m <1>:                                su invocation.       (line  69)
* -m <2>:                                uname invocation.    (line  41)
* -m <3>:                                who invocation.      (line  62)
* -m <4>:                                du invocation.       (line 106)
* -m <5>:                                touch invocation.    (line  90)
* -m <6>:                                readlink invocation. (line  43)
* -m <7>:                                mknod invocation.    (line  48)
* -m <8>:                                mkfifo invocation.   (line  21)
* -m <9>:                                mkdir invocation.    (line  19)
* -m <10>:                               install invocation.  (line  74)
* -m:                                    General output formatting.
                                                              (line  78)
* -M:                                    sort invocation.     (line 149)
* -m <1>:                                sort invocation.     (line  32)
* -m <2>:                                wc invocation.       (line  47)
* -m:                                    pr invocation.       (line 160)
* -n <1>:                                nice invocation.     (line  47)
* -n <2>:                                uname invocation.    (line  46)
* -n <3>:                                id invocation.       (line  34)
* -n <4>:                                String tests.        (line  19)
* -n <5>:                                echo invocation.     (line  22)
* -n <6>:                                readlink invocation. (line  48)
* -n <7>:                                ln invocation.       (line 110)
* -n <8>:                                mv invocation.       (line  74)
* -n:                                    cp invocation.       (line 155)
* -N:                                    Formatting the file names.
                                                              (line  17)
* -n <1>:                                What information is listed.
                                                              (line 234)
* -n <2>:                                cut invocation.      (line  55)
* -n <3>:                                shuf invocation.     (line  32)
* -n <4>:                                sort invocation.     (line 159)
* -n <5>:                                csplit invocation.   (line  80)
* -n <6>:                                tail invocation.     (line 153)
* -n:                                    head invocation.     (line  39)
* -N:                                    pr invocation.       (line 194)
* -n:                                    pr invocation.       (line 173)
* -N:                                    od invocation.       (line  71)
* -n <1>:                                nl invocation.       (line  95)
* -n:                                    cat invocation.      (line  31)
* -n NUMBER:                             shred invocation.    (line 106)
* -ne:                                   Numeric tests.       (line  16)
* -nt:                                   File characteristic tests.
                                                              (line  15)
* -o <1>:                                stdbuf invocation.   (line  23)
* -o <2>:                                uname invocation.    (line  57)
* -o:                                    Connectives for test.
                                                              (line  15)
* -O:                                    Access permission tests.
                                                              (line  28)
* -o <1>:                                truncate invocation. (line  26)
* -o <2>:                                install invocation.  (line  86)
* -o <3>:                                What information is listed.
                                                              (line 238)
* -o <4>:                                shuf invocation.     (line  37)
* -o <5>:                                sort invocation.     (line 276)
* -o <6>:                                pr invocation.       (line 200)
* -o:                                    od invocation.       (line 197)
* -ot:                                   File characteristic tests.
                                                              (line  19)
* -p:                                    su invocation.       (line  69)
* -P:                                    chcon invocation.    (line  42)
* -p <1>:                                uname invocation.    (line  50)
* -p:                                    who invocation.      (line  66)
* -P:                                    pwd invocation.      (line  22)
* -p:                                    mktemp invocation.   (line 106)
* -P:                                    pathchk invocation.  (line  42)
* -p <1>:                                pathchk invocation.  (line  29)
* -p:                                    File type tests.     (line  28)
* -P <1>:                                du invocation.       (line 112)
* -P <2>:                                df invocation.       (line  85)
* -P <3>:                                chgrp invocation.    (line  79)
* -P:                                    chown invocation.    (line 152)
* -p <1>:                                rmdir invocation.    (line  22)
* -p:                                    mkdir invocation.    (line  39)
* -P:                                    ln invocation.       (line 129)
* -p <1>:                                install invocation.  (line  98)
* -p:                                    cp invocation.       (line 168)
* -P:                                    cp invocation.       (line 161)
* -p <1>:                                dircolors invocation.
                                                              (line  45)
* -p <2>:                                General output formatting.
                                                              (line  83)
* -p:                                    nl invocation.       (line 108)
* -P:                                    Traversing symlinks. (line  26)
* -q <1>:                                who invocation.      (line  70)
* -q <2>:                                mktemp invocation.   (line  93)
* -q:                                    readlink invocation. (line  54)
* -Q:                                    Formatting the file names.
                                                              (line  30)
* -q <1>:                                Formatting the file names.
                                                              (line  23)
* -q <2>:                                csplit invocation.   (line 100)
* -q <3>:                                tail invocation.     (line 161)
* -q:                                    head invocation.     (line  46)
* -r <1>:                                runcon invocation.   (line  35)
* -r:                                    chcon invocation.    (line  55)
* -R:                                    chcon invocation.    (line  30)
* -r:                                    uname invocation.    (line  61)
* -R:                                    Options for date.    (line  40)
* -r <1>:                                Options for date.    (line  34)
* -r <2>:                                who invocation.      (line  75)
* -r <3>:                                id invocation.       (line  39)
* -r <4>:                                Access permission tests.
                                                              (line  15)
* -r <5>:                                truncate invocation. (line  30)
* -r:                                    touch invocation.    (line  94)
* -R <1>:                                chmod invocation.    (line  69)
* -R <2>:                                chgrp invocation.    (line  66)
* -R <3>:                                chown invocation.    (line 140)
* -R:                                    rm invocation.       (line  91)
* -r <1>:                                rm invocation.       (line  91)
* -r:                                    cp invocation.       (line 253)
* -R:                                    cp invocation.       (line 253)
* -r:                                    Sorting the output.  (line  27)
* -R <1>:                                Which files are listed.
                                                              (line  91)
* -R:                                    sort invocation.     (line 188)
* -r <1>:                                sort invocation.     (line 182)
* -r <2>:                                sum invocation.      (line  25)
* -r <3>:                                pr invocation.       (line 207)
* -r:                                    tac invocation.      (line  26)
* -s <1>:                                timeout invocation.  (line  34)
* -s <2>:                                su invocation.       (line  80)
* -s <3>:                                uname invocation.    (line  65)
* -s <4>:                                Options for date.    (line  82)
* -s <5>:                                who invocation.      (line  79)
* -s <6>:                                tty invocation.      (line  18)
* -s:                                    File characteristic tests.
                                                              (line  12)
* -S:                                    File type tests.     (line  31)
* -s:                                    truncate invocation. (line  34)
* -S:                                    du invocation.       (line 140)
* -s <1>:                                du invocation.       (line 136)
* -s:                                    readlink invocation. (line  54)
* -S:                                    ln invocation.       (line 144)
* -s:                                    ln invocation.       (line 138)
* -S <1>:                                mv invocation.       (line  98)
* -S:                                    install invocation.  (line 115)
* -s:                                    install invocation.  (line 108)
* -S:                                    cp invocation.       (line 336)
* -s:                                    cp invocation.       (line 328)
* -S:                                    Sorting the output.  (line  32)
* -s <1>:                                What information is listed.
                                                              (line 244)
* -s <2>:                                paste invocation.    (line  34)
* -s <3>:                                cut invocation.      (line  59)
* -s:                                    uniq invocation.     (line  41)
* -S:                                    sort invocation.     (line 300)
* -s <1>:                                sort invocation.     (line 294)
* -s <2>:                                sum invocation.      (line  31)
* -s <3>:                                csplit invocation.   (line 100)
* -s:                                    fold invocation.     (line  29)
* -S:                                    pr invocation.       (line 221)
* -s <1>:                                pr invocation.       (line 212)
* -s <2>:                                fmt invocation.      (line  47)
* -s:                                    od invocation.       (line 200)
* -S:                                    od invocation.       (line  76)
* -s <1>:                                nl invocation.       (line 112)
* -s <2>:                                tac invocation.      (line  33)
* -s:                                    cat invocation.      (line  35)
* -S:                                    Backup options.      (line  50)
* -s BYTES:                              shred invocation.    (line 117)
* -su:                                   su invocation.       (line  27)
* -t <1>:                                runcon invocation.   (line  39)
* -t:                                    chcon invocation.    (line  59)
* -T:                                    who invocation.      (line  95)
* -t <1>:                                who invocation.      (line  83)
* -t <2>:                                mktemp invocation.   (line 122)
* -t <3>:                                File type tests.     (line  34)
* -t:                                    stat invocation.     (line  53)
* -T:                                    df invocation.       (line 124)
* -t:                                    df invocation.       (line 118)
* -T:                                    ln invocation.       (line 153)
* -t:                                    ln invocation.       (line 149)
* -T:                                    mv invocation.       (line 107)
* -t:                                    mv invocation.       (line 103)
* -T:                                    install invocation.  (line 124)
* -t:                                    install invocation.  (line 120)
* -T:                                    cp invocation.       (line 345)
* -t:                                    cp invocation.       (line 341)
* -T:                                    General output formatting.
                                                              (line  92)
* -t <1>:                                Sorting the output.  (line  36)
* -t <2>:                                unexpand invocation. (line  24)
* -t:                                    expand invocation.   (line  22)
* -T:                                    sort invocation.     (line 336)
* -t <1>:                                sort invocation.     (line 316)
* -t:                                    md5sum invocation.   (line  87)
* -T:                                    pr invocation.       (line 242)
* -t <1>:                                pr invocation.       (line 231)
* -t <2>:                                fmt invocation.      (line  40)
* -t:                                    od invocation.       (line  85)
* -T:                                    cat invocation.      (line  43)
* -t:                                    cat invocation.      (line  39)
* -u <1>:                                env invocation.      (line  90)
* -u <2>:                                runcon invocation.   (line  31)
* -u <3>:                                chcon invocation.    (line  51)
* -u <4>:                                Options for date.    (line  87)
* -u <5>:                                who invocation.      (line  86)
* -u <6>:                                id invocation.       (line  44)
* -u <7>:                                mktemp invocation.   (line  98)
* -u <8>:                                Access permission tests.
                                                              (line  18)
* -u <9>:                                shred invocation.    (line 123)
* -u <10>:                               mv invocation.       (line  80)
* -u:                                    cp invocation.       (line 350)
* -U:                                    Sorting the output.  (line  49)
* -u <1>:                                Sorting the output.  (line  42)
* -u <2>:                                uniq invocation.     (line 101)
* -u <3>:                                sort invocation.     (line 345)
* -u <4>:                                fmt invocation.      (line  53)
* -u:                                    cat invocation.      (line  46)
* -v <1>:                                chcon invocation.    (line  47)
* -v <2>:                                uname invocation.    (line  76)
* -v <3>:                                chmod invocation.    (line  59)
* -v <4>:                                chgrp invocation.    (line  58)
* -v <5>:                                chown invocation.    (line 132)
* -v <6>:                                rmdir invocation.    (line  31)
* -v <7>:                                readlink invocation. (line  58)
* -v <8>:                                mkdir invocation.    (line  60)
* -v <9>:                                ln invocation.       (line 158)
* -v <10>:                               shred invocation.    (line 129)
* -v <11>:                               rm invocation.       (line  95)
* -v <12>:                               mv invocation.       (line  90)
* -v <13>:                               install invocation.  (line 129)
* -v <14>:                               cp invocation.       (line 360)
* -v:                                    Sorting the output.  (line  56)
* -V:                                    sort invocation.     (line 176)
* -v <1>:                                tail invocation.     (line 165)
* -v <2>:                                head invocation.     (line  50)
* -v <3>:                                pr invocation.       (line 247)
* -v <4>:                                od invocation.       (line 155)
* -v <5>:                                nl invocation.       (line 117)
* -v:                                    cat invocation.      (line  50)
* -w <1>:                                who invocation.      (line  95)
* -w <2>:                                Access permission tests.
                                                              (line  21)
* -w <3>:                                General output formatting.
                                                              (line 104)
* -w <4>:                                uniq invocation.     (line 106)
* -w <5>:                                md5sum invocation.   (line  96)
* -w <6>:                                wc invocation.       (line  51)
* -w:                                    fold invocation.     (line  35)
* -W:                                    pr invocation.       (line 260)
* -w <1>:                                pr invocation.       (line 251)
* -w <2>:                                fmt invocation.      (line  59)
* -w <3>:                                base64 invocation.   (line  22)
* -w <4>:                                od invocation.       (line 162)
* -w:                                    nl invocation.       (line 122)
* -WIDTH:                                fmt invocation.      (line  59)
* -x <1>:                                Access permission tests.
                                                              (line  24)
* -x <2>:                                du invocation.       (line 201)
* -x <3>:                                df invocation.       (line 149)
* -x <4>:                                shred invocation.    (line 134)
* -x <5>:                                cp invocation.       (line 364)
* -x:                                    General output formatting.
                                                              (line  88)
* -X:                                    Sorting the output.  (line  63)
* -x:                                    od invocation.       (line 203)
* -X FILE:                               du invocation.       (line 211)
* -Z:                                    id invocation.       (line  48)
* -z:                                    String tests.        (line  15)
* -Z <1>:                                mknod invocation.    (line  57)
* -Z <2>:                                mkfifo invocation.   (line  30)
* -Z:                                    mkdir invocation.    (line  65)
* -z:                                    shred invocation.    (line 144)
* -Z <1>:                                install invocation.  (line 133)
* -Z:                                    What information is listed.
                                                              (line 268)
* -z <1>:                                uniq invocation.     (line 112)
* -z <2>:                                shuf invocation.     (line  48)
* -z <3>:                                sort invocation.     (line 359)
* -z:                                    csplit invocation.   (line  89)
* .cshrc:                                su invocation.       (line  48)
* /:                                     Numeric expressions. (line  16)
* /bin/sh:                               su invocation.       (line  14)
* /etc/passwd:                           su invocation.       (line  14)
* /etc/shells:                           su invocation.       (line  69)
* 128-bit checksum:                      md5sum invocation.   (line   6)
* 16-bit checksum:                       sum invocation.      (line   6)
* 160-bit checksum:                      sha1sum invocation.  (line   6)
* 224-bit checksum:                      sha2 utilities.      (line   6)
* 256-bit checksum:                      sha2 utilities.      (line   6)
* 384-bit checksum:                      sha2 utilities.      (line   6)
* 4.2 file system type:                  df invocation.       (line 136)
* 512-bit checksum:                      sha2 utilities.      (line   6)
* <:                                     Relations for expr.  (line  22)
* <=:                                    Relations for expr.  (line  22)
* = <1>:                                 Relations for expr.  (line  22)
* =:                                     String tests.        (line  22)
* ==:                                    Relations for expr.  (line  22)
* >:                                     Relations for expr.  (line  22)
* >=:                                    Relations for expr.  (line  22)
* \( regexp operator:                    String expressions.  (line  24)
* \+ regexp operator:                    String expressions.  (line  28)
* \? regexp operator:                    String expressions.  (line  28)
* \c:                                    printf invocation.   (line  29)
* \OOO:                                  printf invocation.   (line  65)
* \uhhhh:                                printf invocation.   (line  72)
* \Uhhhhhhhh:                            printf invocation.   (line  72)
* \xHH:                                  printf invocation.   (line  65)
* \| regexp operator:                    String expressions.  (line  28)
* _POSIX2_VERSION <1>:                   touch invocation.    (line 113)
* _POSIX2_VERSION <2>:                   uniq invocation.     (line  46)
* _POSIX2_VERSION <3>:                   sort invocation.     (line 392)
* _POSIX2_VERSION <4>:                   tail invocation.     (line 176)
* _POSIX2_VERSION:                       Standards conformance.
                                                              (line  19)
* abbreviations for months:              Calendar date items. (line  38)
* access permission tests:               Access permission tests.
                                                              (line   6)
* access permissions, changing:          chmod invocation.    (line   6)
* access time:                           dd invocation.       (line 213)
* access time, changing:                 touch invocation.    (line  53)
* access time, printing or sorting files by: Sorting the output.
                                                              (line  42)
* access time, show the most recent:     du invocation.       (line 159)
* across columns:                        pr invocation.       (line  82)
* across, listing files:                 General output formatting.
                                                              (line  88)
* adding permissions:                    Setting Permissions. (line  38)
* addition:                              Numeric expressions. (line  12)
* ago in date strings:                   Relative items in date strings.
                                                              (line  23)
* all repeated lines, outputting:        uniq invocation.     (line  69)
* alnum:                                 Character sets.      (line  92)
* alpha:                                 Character sets.      (line  95)
* alternate ebcdic, converting to:       dd invocation.       (line  85)
* always color option:                   General output formatting.
                                                              (line  27)
* always interactive option:             rm invocation.       (line  57)
* am i:                                  who invocation.      (line  21)
* am in date strings:                    Time of day items.   (line  22)
* and operator <1>:                      Relations for expr.  (line  17)
* and operator:                          Connectives for test.
                                                              (line  12)
* append:                                dd invocation.       (line 169)
* appending to the output file:          dd invocation.       (line 169)
* appropriate privileges <1>:            nice invocation.     (line   6)
* appropriate privileges <2>:            hostname invocation. (line   6)
* appropriate privileges <3>:            Setting the time.    (line   6)
* appropriate privileges:                install invocation.  (line  86)
* arbitrary date strings, parsing:       Options for date.    (line  11)
* arbitrary text, displaying:            echo invocation.     (line   6)
* arch:                                  arch invocation.     (line   6)
* arithmetic tests:                      Numeric tests.       (line   6)
* ASCII dump of files:                   od invocation.       (line   6)
* ascii, converting to:                  dd invocation.       (line  77)
* atime, changing:                       touch invocation.    (line  53)
* atime, printing or sorting files by:   Sorting the output.  (line  42)
* atime, show the most recent:           du invocation.       (line 159)
* attributes, file:                      Changing file attributes.
                                                              (line   6)
* authors of get_date:                   Authors of get_date. (line   6)
* auto color option:                     General output formatting.
                                                              (line  25)
* automounter file systems:              df invocation.       (line  32)
* b for block special file:              mknod invocation.    (line  31)
* background jobs, stopping at terminal write: Local.         (line  41)
* backslash escapes <1>:                 echo invocation.     (line  25)
* backslash escapes:                     Character sets.      (line  14)
* backslash sequences for file names:    Formatting the file names.
                                                              (line  11)
* backup files, ignoring:                Which files are listed.
                                                              (line  23)
* backup options:                        Backup options.      (line   6)
* backup suffix:                         Backup options.      (line  50)
* backups, making <1>:                   ln invocation.       (line  84)
* backups, making <2>:                   mv invocation.       (line  56)
* backups, making <3>:                   install invocation.  (line  42)
* backups, making <4>:                   cp invocation.       (line  75)
* backups, making:                       Backup options.      (line  13)
* backups, making only:                  cp invocation.       (line  53)
* base64:                                base64 invocation.   (line   6)
* Base64 decoding:                       base64 invocation.   (line  30)
* base64 encoding:                       base64 invocation.   (line   6)
* basename:                              basename invocation. (line   6)
* baud rate, setting:                    Special.             (line  43)
* beeping at input buffer full:          Input.               (line  59)
* beginning of time:                     Time conversion specifiers.
                                                              (line  41)
* beginning of time, for POSIX:          Seconds since the Epoch.
                                                              (line  13)
* Bellovin, Steven M.:                   Authors of get_date. (line   6)
* Berets, Jim:                           Authors of get_date. (line   6)
* Berry, K. <1>:                         Authors of get_date. (line  14)
* Berry, K.:                             Introduction.        (line  19)
* binary:                                dd invocation.       (line 230)
* binary I/O:                            dd invocation.       (line 230)
* binary input files:                    md5sum invocation.   (line  38)
* blank:                                 Character sets.      (line  98)
* blank lines, numbering:                nl invocation.       (line  87)
* blanks, ignoring leading:              sort invocation.     (line  79)
* block (space-padding):                 dd invocation.       (line  94)
* block size <1>:                        dd invocation.       (line  33)
* block size:                            Block size.          (line   6)
* block size of conversion:              dd invocation.       (line  40)
* block size of input:                   dd invocation.       (line  25)
* block size of output:                  dd invocation.       (line  29)
* block special check:                   File type tests.     (line  10)
* block special files:                   mknod invocation.    (line  11)
* block special files, creating:         mknod invocation.    (line   6)
* BLOCK_SIZE:                            Block size.          (line  12)
* BLOCKSIZE:                             Block size.          (line  12)
* body, numbering:                       nl invocation.       (line  17)
* Bourne shell syntax for color setup:   dircolors invocation.
                                                              (line  34)
* breaks, cause interrupts:              Input.               (line  12)
* breaks, ignoring:                      Input.               (line   9)
* brkint:                                Input.               (line  12)
* bs:                                    dd invocation.       (line  33)
* BSD sum:                               sum invocation.      (line  25)
* BSD tail:                              tail invocation.     (line  19)
* BSD touch compatibility:               touch invocation.    (line  71)
* bsN:                                   Output.              (line  55)
* bugs, reporting:                       Introduction.        (line  12)
* built-in shell commands, conflicts with <1>: sleep invocation.
                                                              (line  34)
* built-in shell commands, conflicts with <2>: kill invocation.
                                                              (line  13)
* built-in shell commands, conflicts with <3>: nice invocation.
                                                              (line  37)
* built-in shell commands, conflicts with <4>: pwd invocation.
                                                              (line  30)
* built-in shell commands, conflicts with <5>: test invocation.
                                                              (line  28)
* built-in shell commands, conflicts with <6>: printf invocation.
                                                              (line  16)
* built-in shell commands, conflicts with <7>: echo invocation.
                                                              (line  11)
* built-in shell commands, conflicts with <8>: stat invocation.
                                                              (line  15)
* built-in shell commands, conflicts with: mknod invocation.  (line  20)
* byte count:                            wc invocation.       (line   6)
* byte-swapping:                         dd invocation.       (line 123)
* c for character special file:          mknod invocation.    (line  34)
* C shell syntax for color setup:        dircolors invocation.
                                                              (line  40)
* C-s/C-q flow control:                  Input.               (line  40)
* calendar date item:                    Calendar date items. (line   6)
* canonical file name:                   readlink invocation. (line   6)
* canonicalize a file name:              readlink invocation. (line   6)
* case folding:                          sort invocation.     (line  94)
* case translation:                      Local.               (line  36)
* case, ignored in dates:                General date syntax. (line  64)
* cat:                                   cat invocation.      (line   6)
* cbreak:                                Combination.         (line  52)
* cbs:                                   dd invocation.       (line  40)
* CD-ROM file system type:               df invocation.       (line 140)
* cdfs file system type:                 df invocation.       (line 140)
* cdtrdsr:                               Control.             (line  39)
* change or print terminal settings:     stty invocation.     (line   6)
* change SELinux context:                chcon invocation.    (line   6)
* changed files, verbosely describing:   chgrp invocation.    (line  20)
* changed owners, verbosely describing:  chown invocation.    (line  70)
* changing access permissions:           chmod invocation.    (line   6)
* changing file attributes:              Changing file attributes.
                                                              (line   6)
* changing file ownership:               chown invocation.    (line   6)
* changing file timestamps:              touch invocation.    (line   6)
* changing group ownership <1>:          chgrp invocation.    (line   6)
* changing group ownership:              chown invocation.    (line   6)
* changing security context:             chcon invocation.    (line   6)
* changing special mode bits:            Changing Special Mode Bits.
                                                              (line   6)
* character classes:                     Character sets.      (line  79)
* character count:                       wc invocation.       (line   6)
* character size:                        Control.             (line  19)
* character special check:               File type tests.     (line  13)
* character special files:               mknod invocation.    (line  11)
* character special files, creating:     mknod invocation.    (line   6)
* characters, special:                   Characters.          (line   6)
* chcon:                                 chcon invocation.    (line   6)
* check file types:                      test invocation.     (line   6)
* checking for sortedness:               sort invocation.     (line  18)
* checksum, 128-bit:                     md5sum invocation.   (line   6)
* checksum, 16-bit:                      sum invocation.      (line   6)
* checksum, 160-bit:                     sha1sum invocation.  (line   6)
* checksum, 224-bit:                     sha2 utilities.      (line   6)
* checksum, 256-bit:                     sha2 utilities.      (line   6)
* checksum, 384-bit:                     sha2 utilities.      (line   6)
* checksum, 512-bit:                     sha2 utilities.      (line   6)
* chgrp:                                 chgrp invocation.    (line   6)
* chmod:                                 chmod invocation.    (line   6)
* chown:                                 chown invocation.    (line   6)
* chroot:                                chroot invocation.   (line   6)
* cio:                                   dd invocation.       (line 177)
* cksum:                                 cksum invocation.    (line   6)
* clocal:                                Control.             (line  33)
* clone:                                 cp invocation.       (line 266)
* cntrl:                                 Character sets.      (line 101)
* color database, printing:              dircolors invocation.
                                                              (line  45)
* color setup:                           dircolors invocation.
                                                              (line   6)
* color, distinguishing file types with: General output formatting.
                                                              (line  21)
* cols:                                  Special.             (line  27)
* column to wrap data after:             base64 invocation.   (line  22)
* COLUMNS:                               Special.             (line  30)
* columns:                               Special.             (line  27)
* COLUMNS:                               General output formatting.
                                                              (line 104)
* combination settings:                  Combination.         (line   6)
* comm:                                  comm invocation.     (line   6)
* command-line operands to shuffle:      shuf invocation.     (line  19)
* commands for controlling processes:    Process control.     (line   6)
* commands for delaying:                 Delaying.            (line   6)
* commands for exit status:              Conditions.          (line   6)
* commands for file name manipulation:   File name manipulation.
                                                              (line   6)
* commands for invoking other commands:  Modified command invocation.
                                                              (line   6)
* commands for printing text:            Printing text.       (line   6)
* commands for printing the working context: Working context. (line   6)
* commands for printing user information: User information.   (line   6)
* commands for redirection:              Redirection.         (line   6)
* commands for SELinux context:          SELinux context.     (line   6)
* commands for system context:           System context.      (line   6)
* commas, outputting between files:      General output formatting.
                                                              (line  78)
* comments, in dates:                    General date syntax. (line  64)
* common field, joining on:              join invocation.     (line   6)
* common lines:                          comm invocation.     (line  18)
* common options:                        Common options.      (line   6)
* compare values:                        test invocation.     (line   6)
* comparing sorted files:                comm invocation.     (line   6)
* comparison operators:                  Relations for expr.  (line  22)
* concatenate and write files:           cat invocation.      (line   6)
* concurrent I/O:                        dd invocation.       (line 177)
* conditional executability:             Conditional Executability.
                                                              (line   6)
* conditions:                            Conditions.          (line   6)
* conflicts with shell built-ins <1>:    sleep invocation.    (line  34)
* conflicts with shell built-ins <2>:    kill invocation.     (line  13)
* conflicts with shell built-ins <3>:    nice invocation.     (line  37)
* conflicts with shell built-ins <4>:    pwd invocation.      (line  30)
* conflicts with shell built-ins <5>:    test invocation.     (line  28)
* conflicts with shell built-ins <6>:    printf invocation.   (line  16)
* conflicts with shell built-ins <7>:    echo invocation.     (line  11)
* conflicts with shell built-ins <8>:    stat invocation.     (line  15)
* conflicts with shell built-ins:        mknod invocation.    (line  20)
* connectives, logical <1>:              Relations for expr.  (line   6)
* connectives, logical:                  Connectives for test.
                                                              (line   6)
* context splitting:                     csplit invocation.   (line   6)
* context, system:                       System context.      (line   6)
* control characters, using ^C:          Local.               (line  51)
* control settings:                      Control.             (line   6)
* controlling terminal:                  dd invocation.       (line 218)
* conv:                                  dd invocation.       (line  71)
* conversion block size:                 dd invocation.       (line  40)
* conversion specifiers, date:           Date conversion specifiers.
                                                              (line   6)
* conversion specifiers, literal:        Literal conversion specifiers.
                                                              (line   6)
* conversion specifiers, time:           Time conversion specifiers.
                                                              (line   6)
* converting tabs to spaces:             expand invocation.   (line   6)
* converting while copying a file:       dd invocation.       (line   6)
* cooked:                                Combination.         (line  37)
* Coordinated Universal Time:            Options for date.    (line  87)
* copy on write:                         cp invocation.       (line 266)
* copying directories recursively:       cp invocation.       (line  95)
* copying existing permissions:          Copying Permissions. (line   6)
* copying files:                         cat invocation.      (line   6)
* copying files and directories:         cp invocation.       (line   6)
* copying files and setting attributes:  install invocation.  (line   6)
* core utilities:                        Top.                 (line  18)
* count:                                 dd invocation.       (line  51)
* count_bytes:                           dd invocation.       (line 244)
* COW:                                   cp invocation.       (line 266)
* cp:                                    cp invocation.       (line   6)
* crashes and corruption:                sync invocation.     (line  11)
* CRC checksum:                          cksum invocation.    (line   6)
* cread:                                 Control.             (line  30)
* creating directories:                  mkdir invocation.    (line   6)
* creating FIFOs (named pipes):          mkfifo invocation.   (line   6)
* creating links (hard only):            link invocation.     (line   6)
* creating links (hard or soft):         ln invocation.       (line   6)
* creating output file, avoiding:        dd invocation.       (line 131)
* creating output file, requiring:       dd invocation.       (line 135)
* crN:                                   Output.              (line  45)
* crown margin:                          fmt invocation.      (line  34)
* crt:                                   Combination.         (line  75)
* crterase:                              Local.               (line  22)
* crtkill:                               Local.               (line  56)
* crtscts:                               Control.             (line  36)
* csh syntax for color setup:            dircolors invocation.
                                                              (line  40)
* csN:                                   Control.             (line  19)
* csplit:                                csplit invocation.   (line   6)
* cstopb:                                Control.             (line  27)
* ctime, printing or sorting by:         Sorting the output.  (line  13)
* ctime, show the most recent:           du invocation.       (line 154)
* ctlecho:                               Local.               (line  51)
* current working directory, printing:   pwd invocation.      (line   6)
* cut:                                   cut invocation.      (line   6)
* cyclic redundancy check:               cksum invocation.    (line   6)
* data, erasing:                         shred invocation.    (line   6)
* database for color setup, printing:    dircolors invocation.
                                                              (line  45)
* date:                                  date invocation.     (line   6)
* date conversion specifiers:            Date conversion specifiers.
                                                              (line   6)
* date format, ISO 8601:                 Calendar date items. (line  30)
* date input formats:                    Date input formats.  (line   6)
* date options:                          Options for date.    (line   6)
* date strings, parsing:                 Options for date.    (line  11)
* day in date strings:                   Relative items in date strings.
                                                              (line  15)
* day of week item:                      Day of week items.   (line   6)
* dd:                                    dd invocation.       (line   6)
* dec:                                   Combination.         (line  78)
* decctlq:                               Combination.         (line  63)
* Decode base64 data:                    base64 invocation.   (line  30)
* delay for a specified time:            sleep invocation.    (line   6)
* delaying commands:                     Delaying.            (line   6)
* deleting characters:                   Squeezing.           (line   6)
* dereferencing symbolic links:          ln invocation.       (line  42)
* descriptor follow option:              tail invocation.     (line  48)
* destination directory <1>:             ln invocation.       (line 149)
* destination directory <2>:             mv invocation.       (line 103)
* destination directory <3>:             install invocation.  (line 120)
* destination directory <4>:             cp invocation.       (line 341)
* destination directory:                 Target directory.    (line  15)
* destinations, multiple output:         tee invocation.      (line   6)
* device file, disk:                     df invocation.       (line  19)
* df:                                    df invocation.       (line   6)
* DF_BLOCK_SIZE:                         Block size.          (line  12)
* diagnostic:                            chcon invocation.    (line  47)
* dictionary order:                      sort invocation.     (line  87)
* differing lines:                       comm invocation.     (line  18)
* digit:                                 Character sets.      (line 104)
* dir:                                   dir invocation.      (line   6)
* dircolors:                             dircolors invocation.
                                                              (line   6)
* direct:                                dd invocation.       (line 183)
* direct I/O:                            dd invocation.       (line 183)
* direct statfs for a file:              df invocation.       (line  42)
* directories, copying:                  cp invocation.       (line   6)
* directories, copying recursively:      cp invocation.       (line  95)
* directories, creating:                 mkdir invocation.    (line   6)
* directories, creating with given attributes: install invocation.
                                                              (line  62)
* directories, removing (recursively):   rm invocation.       (line  91)
* directories, removing empty:           rmdir invocation.    (line   6)
* directory:                             dd invocation.       (line 194)
* directory check:                       File type tests.     (line  16)
* directory components, printing:        dirname invocation.  (line   6)
* directory deletion, ignoring failures: rmdir invocation.    (line  17)
* directory deletion, reporting:         rmdir invocation.    (line  31)
* directory I/O:                         dd invocation.       (line 194)
* directory listing:                     ls invocation.       (line   6)
* directory listing, brief:              dir invocation.      (line   6)
* directory listing, recursive:          Which files are listed.
                                                              (line  91)
* directory listing, verbose:            vdir invocation.     (line   6)
* directory order, listing by:           Sorting the output.  (line  20)
* directory, creating temporary:         mktemp invocation.   (line   6)
* directory, stripping from file names:  basename invocation. (line   6)
* dired Emacs mode support:              What information is listed.
                                                              (line  16)
* dirname:                               dirname invocation.  (line   6)
* disabling special characters:          Characters.          (line  13)
* disambiguating group names and IDs:    Disambiguating names and IDs.
                                                              (line   6)
* disk allocation:                       What information is listed.
                                                              (line 244)
* disk device file:                      df invocation.       (line  19)
* disk usage:                            Disk usage.          (line   6)
* disk usage by file system:             df invocation.       (line   6)
* disk usage for files:                  du invocation.       (line   6)
* diskette file system:                  df invocation.       (line 144)
* displacement of dates:                 Relative items in date strings.
                                                              (line   6)
* displaying text:                       echo invocation.     (line   6)
* displaying value of a symbolic link:   readlink invocation. (line   6)
* division:                              Numeric expressions. (line  16)
* do nothing, successfully:              true invocation.     (line   6)
* do nothing, unsuccessfully:            false invocation.    (line   6)
* DOS file system:                       df invocation.       (line 144)
* double spacing:                        pr invocation.       (line  94)
* down columns:                          pr invocation.       (line  68)
* dsusp:                                 Characters.          (line  53)
* dsync:                                 dd invocation.       (line 199)
* DTR/DSR flow control:                  Control.             (line  39)
* du:                                    du invocation.       (line   6)
* DU_BLOCK_SIZE:                         Block size.          (line  12)
* ebcdic, converting to:                 dd invocation.       (line  81)
* echo <1>:                              Local.               (line  18)
* echo:                                  echo invocation.     (line   6)
* echoctl:                               Local.               (line  51)
* echoe:                                 Local.               (line  22)
* echok:                                 Local.               (line  26)
* echoke:                                Local.               (line  56)
* echonl:                                Local.               (line  29)
* echoprt:                               Local.               (line  46)
* effective user and group IDs, printing: id invocation.      (line   6)
* effective user ID, printing:           whoami invocation.   (line   6)
* efs file system type:                  df invocation.       (line 136)
* Eggert, Paul:                          Authors of get_date. (line   6)
* eight-bit characters <1>:              Combination.         (line  55)
* eight-bit characters:                  Control.             (line  19)
* eight-bit input:                       Input.               (line  25)
* ek:                                    Combination.         (line  22)
* empty files, creating:                 touch invocation.    (line  11)
* empty lines, numbering:                nl invocation.       (line  87)
* entire files, output of:               Output of entire files.
                                                              (line   6)
* env:                                   env invocation.      (line   6)
* environment variables, printing:       printenv invocation. (line   6)
* environment, preserving:               su invocation.       (line  69)
* environment, printing:                 env invocation.      (line  45)
* environment, running a program in a modified: env invocation.
                                                              (line   6)
* eof:                                   Characters.          (line  32)
* eol:                                   Characters.          (line  35)
* eol2:                                  Characters.          (line  38)
* epoch, for POSIX:                      Seconds since the Epoch.
                                                              (line  13)
* epoch, seconds since:                  Time conversion specifiers.
                                                              (line  41)
* equal string check:                    String tests.        (line  22)
* equivalence classes:                   Character sets.      (line 128)
* erase:                                 Characters.          (line  26)
* erasing data:                          shred invocation.    (line   6)
* error messages, omitting <1>:          chmod invocation.    (line  45)
* error messages, omitting <2>:          chgrp invocation.    (line  26)
* error messages, omitting:              chown invocation.    (line  76)
* evaluation of expressions:             expr invocation.     (line   6)
* even parity:                           Control.             (line  13)
* evenp:                                 Combination.         (line   9)
* exabyte, definition of:                Block size.          (line 116)
* examples of date:                      Examples of date.    (line   6)
* examples of expr:                      Examples of expr.    (line   6)
* exbibyte, definition of:               Block size.          (line 120)
* excl:                                  dd invocation.       (line 135)
* excluding files from du:               du invocation.       (line 205)
* executable file check:                 Access permission tests.
                                                              (line  24)
* executables and file type, marking:    General output formatting.
                                                              (line  36)
* execute/search permission:             Mode Structure.      (line  18)
* execute/search permission, symbolic:   Setting Permissions. (line  63)
* existence-of-file check:               File characteristic tests.
                                                              (line   9)
* existing backup method:                Backup options.      (line  39)
* exit status commands:                  Conditions.          (line   6)
* exit status of chroot:                 chroot invocation.   (line  58)
* exit status of env:                    env invocation.      (line 100)
* exit status of expr:                   expr invocation.     (line  43)
* exit status of false:                  false invocation.    (line   6)
* exit status of ls:                     ls invocation.       (line  29)
* exit status of mktemp:                 mktemp invocation.   (line 130)
* exit status of nice:                   nice invocation.     (line  56)
* exit status of nohup:                  nohup invocation.    (line  47)
* exit status of pathchk:                pathchk invocation.  (line  50)
* exit status of printenv:               printenv invocation. (line  25)
* exit status of runcon:                 runcon invocation.   (line  46)
* exit status of sort:                   sort invocation.     (line  58)
* exit status of stdbuf:                 stdbuf invocation.   (line  61)
* exit status of su:                     su invocation.       (line  85)
* exit status of test:                   test invocation.     (line  41)
* exit status of timeout:                timeout invocation.  (line  39)
* exit status of true:                   true invocation.     (line   6)
* exit status of tty:                    tty invocation.      (line  21)
* expand:                                expand invocation.   (line   6)
* expr:                                  expr invocation.     (line   6)
* expression evaluation <1>:             expr invocation.     (line   6)
* expression evaluation:                 test invocation.     (line   6)
* expressions, numeric:                  Numeric expressions. (line   6)
* expressions, string:                   String expressions.  (line   6)
* extended attributes, xattr <1>:        mv invocation.       (line  34)
* extended attributes, xattr:            install invocation.  (line  35)
* extension, sorting files by:           Sorting the output.  (line  63)
* factor:                                factor invocation.   (line   6)
* failure exit status:                   false invocation.    (line   6)
* false:                                 false invocation.    (line   6)
* fdatasync:                             dd invocation.       (line 149)
* ffN:                                   Output.              (line  63)
* field separator character:             sort invocation.     (line 316)
* fields, padding numeric:               Padding and other flags.
                                                              (line   6)
* FIFOs, creating:                       mkfifo invocation.   (line   6)
* file attributes, changing:             Changing file attributes.
                                                              (line   6)
* file characteristic tests:             File characteristic tests.
                                                              (line   6)
* file contents, dumping unambiguously:  od invocation.       (line   6)
* file information, preserving:          cp invocation.       (line 236)
* file information, preserving, extended attributes, xattr: cp invocation.
                                                              (line 168)
* file mode bits, numeric:               Numeric Modes.       (line   6)
* file name manipulation:                File name manipulation.
                                                              (line   6)
* file name pattern expansion, disabled: su invocation.       (line  48)
* file names, checking validity and portability: pathchk invocation.
                                                              (line   6)
* file names, creating temporary:        mktemp invocation.   (line   6)
* file names, stripping directory and suffix: basename invocation.
                                                              (line   6)
* file offset radix:                     od invocation.       (line  36)
* file ownership, changing:              chown invocation.    (line   6)
* file sizes:                            du invocation.       (line  50)
* file space usage:                      du invocation.       (line   6)
* file status:                           stat invocation.     (line   6)
* file system disk usage:                df invocation.       (line   6)
* file system sizes:                     df invocation.       (line  38)
* file system space, retrieving current data more slowly: df invocation.
                                                              (line 111)
* file system space, retrieving old data more quickly: df invocation.
                                                              (line  78)
* file system status:                    stat invocation.     (line   6)
* file system types, limiting output to certain: df invocation.
                                                              (line  74)
* file system types, printing:           df invocation.       (line 124)
* file systems:                          stat invocation.     (line  28)
* file systems and hard links:           ln invocation.       (line   6)
* file systems, omitting copying to different: cp invocation. (line 364)
* file timestamps, changing:             touch invocation.    (line   6)
* file type and executables, marking:    General output formatting.
                                                              (line  36)
* file type tests:                       File type tests.     (line   6)
* file type, marking:                    General output formatting.
                                                              (line  47)
* file types:                            Special file types.  (line   9)
* file types, special:                   Special file types.  (line   6)
* file utilities:                        Top.                 (line  18)
* files beginning with -, removing:      rm invocation.       (line  98)
* files, copying:                        cp invocation.       (line   6)
* files, creating:                       truncate invocation. (line  11)
* fingerprint, 128-bit:                  md5sum invocation.   (line   6)
* fingerprint, 160-bit:                  sha1sum invocation.  (line   6)
* fingerprint, 224-bit:                  sha2 utilities.      (line   6)
* fingerprint, 256-bit:                  sha2 utilities.      (line   6)
* fingerprint, 384-bit:                  sha2 utilities.      (line   6)
* fingerprint, 512-bit:                  sha2 utilities.      (line   6)
* first in date strings:                 General date syntax. (line  26)
* first part of files, outputting:       head invocation.     (line   6)
* fixed-length records, converting to variable-length: dd invocation.
                                                              (line  40)
* flow control, hardware:                Control.             (line  36)
* flow control, software:                Input.               (line  45)
* flushing, disabling:                   Local.               (line  32)
* fmt:                                   fmt invocation.      (line   6)
* fold:                                  fold invocation.     (line   6)
* folding long input lines:              fold invocation.     (line   6)
* footers, numbering:                    nl invocation.       (line  17)
* force deletion:                        shred invocation.    (line 101)
* formatting file contents:              Formatting file contents.
                                                              (line   6)
* formatting of numbers in seq:          seq invocation.      (line  24)
* formatting times <1>:                  date invocation.     (line  20)
* formatting times:                      pr invocation.       (line  98)
* fortnight in date strings:             Relative items in date strings.
                                                              (line  15)
* fsync:                                 dd invocation.       (line 153)
* fullblock:                             dd invocation.       (line 238)
* general date syntax:                   General date syntax. (line   6)
* general numeric sort:                  sort invocation.     (line 105)
* get_date:                              Date input formats.  (line   6)
* gibibyte, definition of:               Block size.          (line  99)
* gigabyte, definition of:               Block size.          (line  95)
* giving away permissions:               Umask and Protection.
                                                              (line  12)
* globbing, disabled:                    su invocation.       (line  48)
* GMT:                                   Options for date.    (line  87)
* grand total of disk size, usage and available space: df invocation.
                                                              (line  47)
* grand total of disk space:             du invocation.       (line  55)
* graph:                                 Character sets.      (line 107)
* Greenwich Mean Time:                   Options for date.    (line  87)
* group IDs, disambiguating:             Disambiguating names and IDs.
                                                              (line   6)
* group names, disambiguating:           Disambiguating names and IDs.
                                                              (line   6)
* group owner, default:                  Mode Structure.      (line  31)
* group ownership of installed files, setting: install invocation.
                                                              (line  68)
* group ownership, changing <1>:         chgrp invocation.    (line   6)
* group ownership, changing:             chown invocation.    (line   6)
* group, permissions for:                Setting Permissions. (line  26)
* groups:                                groups invocation.   (line   6)
* growing files:                         tail invocation.     (line  48)
* hangups, immunity to:                  nohup invocation.    (line   6)
* hard link check:                       File characteristic tests.
                                                              (line  23)
* hard link, defined:                    ln invocation.       (line  32)
* hard links:                            dd invocation.       (line 227)
* hard links to directories:             ln invocation.       (line  90)
* hard links to symbolic links:          ln invocation.       (line 161)
* hard links, counting in du:            du invocation.       (line  96)
* hard links, creating <1>:              ln invocation.       (line   6)
* hard links, creating:                  link invocation.     (line   6)
* hard links, preserving:                cp invocation.       (line 108)
* hardware class:                        uname invocation.    (line  41)
* hardware flow control:                 Control.             (line  36)
* hardware platform:                     uname invocation.    (line  35)
* hardware type:                         uname invocation.    (line  41)
* hat notation for control characters:   Local.               (line  51)
* head:                                  head invocation.     (line   6)
* head of output:                        shuf invocation.     (line  32)
* headers, numbering:                    nl invocation.       (line  17)
* help, online:                          Common options.      (line  37)
* hex dump of files:                     od invocation.       (line   6)
* High Sierra file system:               df invocation.       (line 140)
* holes, copying files with:             cp invocation.       (line 289)
* holes, creating files with:            truncate invocation. (line  13)
* HOME:                                  su invocation.       (line  20)
* horizontal, listing files:             General output formatting.
                                                              (line  88)
* host processor type:                   uname invocation.    (line  50)
* hostid:                                hostid invocation.   (line   6)
* hostname <1>:                          hostname invocation. (line   6)
* hostname:                              uname invocation.    (line  46)
* hour in date strings:                  Relative items in date strings.
                                                              (line  15)
* hsfs file system type:                 df invocation.       (line 140)
* human numeric sort:                    sort invocation.     (line 133)
* human-readable output <1>:             du invocation.       (line  81)
* human-readable output <2>:             df invocation.       (line  53)
* human-readable output <3>:             What information is listed.
                                                              (line 116)
* human-readable output:                 Block size.          (line  43)
* hup[cl]:                               Control.             (line  23)
* hurd, author, printing:                What information is listed.
                                                              (line  10)
* ibs:                                   dd invocation.       (line  25)
* icanon:                                Local.               (line  11)
* icrnl:                                 Input.               (line  34)
* id:                                    id invocation.       (line   6)
* idle time:                             who invocation.      (line  86)
* iexten:                                Local.               (line  15)
* if:                                    dd invocation.       (line  17)
* iflag:                                 dd invocation.       (line 158)
* ignbrk:                                Input.               (line   9)
* igncr:                                 Input.               (line  31)
* ignore file systems:                   df invocation.       (line  32)
* Ignore garbage in base64 stream:       base64 invocation.   (line  36)
* ignoring case:                         sort invocation.     (line  94)
* ignpar:                                Input.               (line  15)
* imaxbel:                               Input.               (line  59)
* immunity to hangups:                   nohup invocation.    (line   6)
* implementation, hardware:              uname invocation.    (line  35)
* indenting lines:                       pr invocation.       (line 200)
* index:                                 String expressions.  (line  45)
* information, about current users:      who invocation.      (line   6)
* initial part of files, outputting:     head invocation.     (line   6)
* initial tabs, converting:              expand invocation.   (line  34)
* inlcr:                                 Input.               (line  28)
* inode number, printing:                What information is listed.
                                                              (line 123)
* inode usage:                           df invocation.       (line  63)
* inode, and hard links:                 ln invocation.       (line  32)
* inodes, written buffered:              sync invocation.     (line   6)
* inpck:                                 Input.               (line  22)
* input block size:                      dd invocation.       (line  25)
* input encoding, UTF-8:                 Input.               (line  37)
* input range to shuffle:                shuf invocation.     (line  23)
* input settings:                        Input.               (line   6)
* input tabs:                            pr invocation.       (line 118)
* install:                               install invocation.  (line   6)
* intr:                                  Characters.          (line  20)
* invocation of commands, modified:      Modified command invocation.
                                                              (line   6)
* isig:                                  Local.               (line   7)
* ISO 8601 date format:                  Calendar date items. (line  30)
* ISO/IEC 10646:                         printf invocation.   (line  72)
* ispeed:                                Special.             (line  16)
* istrip:                                Input.               (line  25)
* items in date strings:                 General date syntax. (line   6)
* iterations, selecting the number of:   shred invocation.    (line 106)
* iuclc:                                 Input.               (line  50)
* iutf8:                                 Input.               (line  37)
* ixany:                                 Input.               (line  55)
* ixoff:                                 Input.               (line  45)
* ixon:                                  Input.               (line  40)
* join:                                  join invocation.     (line   6)
* kernel name:                           uname invocation.    (line  65)
* kernel release:                        uname invocation.    (line  61)
* kernel version:                        uname invocation.    (line  76)
* kibibyte, definition of:               Block size.          (line  83)
* kibibytes for file sizes:              du invocation.       (line  90)
* kibibytes for file system sizes:       df invocation.       (line  68)
* kill <1>:                              kill invocation.     (line   6)
* kill:                                  Characters.          (line  29)
* kilobyte, definition of:               Block size.          (line  78)
* Knuth, Donald E.:                      fmt invocation.      (line  19)
* language, in dates:                    General date syntax. (line  40)
* last DAY <1>:                          Day of week items.   (line  15)
* last DAY:                              Options for date.    (line  11)
* last in date strings:                  General date syntax. (line  26)
* last modified dates, displaying in du: du invocation.       (line 148)
* last part of files, outputting:        tail invocation.     (line   6)
* LC_ALL <1>:                            ls invocation.       (line  17)
* LC_ALL:                                sort invocation.     (line  49)
* LC_COLLATE <1>:                        Relations for expr.  (line  22)
* LC_COLLATE <2>:                        join invocation.     (line  14)
* LC_COLLATE <3>:                        comm invocation.     (line  12)
* LC_COLLATE <4>:                        uniq invocation.     (line  21)
* LC_COLLATE:                            sort invocation.     (line  49)
* LC_CTYPE <1>:                          printf invocation.   (line  72)
* LC_CTYPE:                              sort invocation.     (line  79)
* LC_MESSAGES:                           pr invocation.       (line  13)
* LC_NUMERIC <1>:                        printf invocation.   (line  59)
* LC_NUMERIC <2>:                        sort invocation.     (line 105)
* LC_NUMERIC:                            Block size.          (line  57)
* LC_TIME <1>:                           date invocation.     (line  11)
* LC_TIME <2>:                           du invocation.       (line 168)
* LC_TIME <3>:                           Formatting file timestamps.
                                                              (line  30)
* LC_TIME <4>:                           sort invocation.     (line 149)
* LC_TIME:                               pr invocation.       (line 105)
* LCASE:                                 Combination.         (line  71)
* lcase:                                 Combination.         (line  71)
* lcase, converting to:                  dd invocation.       (line 105)
* lchown <1>:                            chgrp invocation.    (line  30)
* lchown:                                chown invocation.    (line 103)
* leading directories, creating missing: install invocation.  (line  62)
* leading directory components, stripping: basename invocation.
                                                              (line   6)
* left margin:                           pr invocation.       (line 200)
* length:                                String expressions.  (line  50)
* limiting output of du:                 du invocation.       (line 116)
* line:                                  Special.             (line  37)
* line buffered:                         stdbuf invocation.   (line   6)
* line count:                            wc invocation.       (line   6)
* line numbering:                        nl invocation.       (line   6)
* line settings of terminal:             stty invocation.     (line   6)
* line-breaking:                         fmt invocation.      (line  19)
* line-by-line comparison:               comm invocation.     (line   6)
* LINES:                                 Special.             (line  30)
* link:                                  link invocation.     (line   6)
* links, creating <1>:                   ln invocation.       (line   6)
* links, creating:                       link invocation.     (line   6)
* Linux file system types:               df invocation.       (line 136)
* literal conversion specifiers:         Literal conversion specifiers.
                                                              (line   6)
* litout:                                Combination.         (line  59)
* ln:                                    ln invocation.       (line   6)
* ln format for nl:                      nl invocation.       (line  98)
* lnext:                                 Characters.          (line  62)
* local file system types:               df invocation.       (line 136)
* local settings:                        Local.               (line   6)
* logging out and continuing to run:     nohup invocation.    (line   6)
* logical and operator <1>:              Relations for expr.  (line  17)
* logical and operator:                  Connectives for test.
                                                              (line  12)
* logical connectives <1>:               Relations for expr.  (line   6)
* logical connectives:                   Connectives for test.
                                                              (line   6)
* logical or operator <1>:               Relations for expr.  (line  11)
* logical or operator:                   Connectives for test.
                                                              (line  15)
* logical pages, numbering on:           nl invocation.       (line  12)
* login name, printing:                  logname invocation.  (line   6)
* login sessions, printing users with:   users invocation.    (line   6)
* login shell:                           su invocation.       (line  20)
* login shell, creating:                 su invocation.       (line  57)
* login time:                            who invocation.      (line  11)
* LOGNAME:                               su invocation.       (line  20)
* logname:                               logname invocation.  (line   6)
* long ls format:                        What information is listed.
                                                              (line 131)
* lower:                                 Character sets.      (line 110)
* lowercase, translating to output:      Output.              (line  12)
* ls:                                    ls invocation.       (line   6)
* LS_BLOCK_SIZE:                         Block size.          (line  12)
* LS_COLORS:                             dircolors invocation.
                                                              (line  23)
* lutimes:                               touch invocation.    (line  75)
* machine type:                          uname invocation.    (line  41)
* machine-readable stty output:          stty invocation.     (line  41)
* MacKenzie, D.:                         Introduction.        (line  19)
* MacKenzie, David:                      Authors of get_date. (line   6)
* Makefiles, installing programs in:     install invocation.  (line  30)
* manipulating files:                    Basic operations.    (line   6)
* manipulation of file names:            File name manipulation.
                                                              (line   6)
* match:                                 String expressions.  (line  36)
* matching patterns:                     String expressions.  (line  11)
* MD5:                                   md5sum invocation.   (line   6)
* md5sum:                                md5sum invocation.   (line   6)
* mebibyte, definition of:               Block size.          (line  92)
* mebibytes for file sizes:              du invocation.       (line 106)
* megabyte, definition of:               Block size.          (line  88)
* merging files:                         paste invocation.    (line   6)
* merging files in parallel:             pr invocation.       (line   6)
* merging sorted files:                  sort invocation.     (line  32)
* message status:                        who invocation.      (line  95)
* message-digest, 128-bit:               md5sum invocation.   (line   6)
* message-digest, 160-bit:               sha1sum invocation.  (line   6)
* message-digest, 224-bit:               sha2 utilities.      (line   6)
* message-digest, 256-bit:               sha2 utilities.      (line   6)
* message-digest, 384-bit:               sha2 utilities.      (line   6)
* message-digest, 512-bit:               sha2 utilities.      (line   6)
* Meyering, J.:                          Introduction.        (line  19)
* Meyering, Jim:                         Authors of get_date. (line   6)
* midnight in date strings:              Time of day items.   (line  22)
* min:                                   Special.             (line   7)
* minute in date strings:                Relative items in date strings.
                                                              (line  15)
* minutes, time zone correction by:      Time of day items.   (line  30)
* mkdir:                                 mkdir invocation.    (line   6)
* mkfifo:                                mkfifo invocation.   (line   6)
* mknod:                                 mknod invocation.    (line   6)
* mktemp:                                mktemp invocation.   (line   6)
* modem control:                         Control.             (line  33)
* modes and umask:                       Umask and Protection.
                                                              (line   6)
* modes of created directories, setting: mkdir invocation.    (line  19)
* modes of created FIFOs, setting:       mkfifo invocation.   (line  21)
* modification time, sorting files by:   Sorting the output.  (line  36)
* modified command invocation:           Modified command invocation.
                                                              (line   6)
* modified environment, running a program in a: env invocation.
                                                              (line   6)
* modify time, changing:                 touch invocation.    (line  90)
* month in date strings:                 Relative items in date strings.
                                                              (line  15)
* month names in date strings:           Calendar date items. (line  38)
* months, sorting by:                    sort invocation.     (line 149)
* months, written-out:                   General date syntax. (line  36)
* MS-DOS file system:                    df invocation.       (line 144)
* mtime, changing:                       touch invocation.    (line  90)
* multicolumn output, generating:        pr invocation.       (line   6)
* multiple changes to permissions:       Multiple Changes.    (line   6)
* multiplication:                        Numeric expressions. (line  16)
* multipliers after numbers:             dd invocation.       (line 258)
* mv:                                    mv invocation.       (line   6)
* name follow option:                    tail invocation.     (line  48)
* name of kernel:                        uname invocation.    (line  65)
* named pipe check:                      File type tests.     (line  28)
* named pipes, creating:                 mkfifo invocation.   (line   6)
* network node name:                     uname invocation.    (line  46)
* never interactive option:              rm invocation.       (line  52)
* newer files, copying only:             cp invocation.       (line 350)
* newer files, moving only:              mv invocation.       (line  80)
* newer-than file check:                 File characteristic tests.
                                                              (line  15)
* newline echoing after kill:            Local.               (line  26)
* newline, echoing:                      Local.               (line  29)
* newline, translating to crlf:          Output.              (line  19)
* newline, translating to return:        Input.               (line  28)
* next DAY <1>:                          Day of week items.   (line  15)
* next DAY:                              Options for date.    (line  11)
* next in date strings:                  General date syntax. (line  26)
* NFS file system type:                  df invocation.       (line 131)
* NFS mounts from BSD to HP-UX <1>:      du invocation.       (line 216)
* NFS mounts from BSD to HP-UX:          What information is listed.
                                                              (line 252)
* nice:                                  nice invocation.     (line   6)
* niceness:                              nice invocation.     (line   6)
* nl <1>:                                Combination.         (line  18)
* nl:                                    nl invocation.       (line   6)
* nlN:                                   Output.              (line  39)
* no dereference:                        chcon invocation.    (line  22)
* no-op:                                 true invocation.     (line   6)
* noatime:                               dd invocation.       (line 213)
* nocreat:                               dd invocation.       (line 131)
* noctty:                                dd invocation.       (line 218)
* node name:                             uname invocation.    (line  46)
* noerror:                               dd invocation.       (line 128)
* noflsh:                                Local.               (line  32)
* nofollow:                              dd invocation.       (line 224)
* nohup:                                 nohup invocation.    (line   6)
* nohup.out:                             nohup invocation.    (line   6)
* nolinks:                               dd invocation.       (line 227)
* non-directories, copying as special files: cp invocation.   (line  95)
* non-directory suffix, stripping:       dirname invocation.  (line   6)
* nonblock:                              dd invocation.       (line 210)
* nonblocking I/O:                       dd invocation.       (line 210)
* none backup method:                    Backup options.      (line  31)
* none color option:                     General output formatting.
                                                              (line  23)
* none dd status=:                       dd invocation.       (line  66)
* none, sorting option for ls:           Sorting the output.  (line  49)
* nonempty file check:                   File characteristic tests.
                                                              (line  12)
* nonprinting characters, ignoring:      sort invocation.     (line 142)
* nonzero-length string check:           String tests.        (line  19)
* noon in date strings:                  Time of day items.   (line  22)
* not-equal string check:                String tests.        (line  25)
* notrunc:                               dd invocation.       (line 141)
* now in date strings:                   Relative items in date strings.
                                                              (line  33)
* noxfer dd status=:                     dd invocation.       (line  62)
* nproc:                                 nproc invocation.    (line   6)
* number of inputs to merge, nmerge:     sort invocation.     (line 250)
* numbered backup method:                Backup options.      (line  35)
* numbering lines:                       nl invocation.       (line   6)
* numbers, written-out:                  General date syntax. (line  26)
* numeric expressions:                   Numeric expressions. (line   6)
* numeric field padding:                 Padding and other flags.
                                                              (line   6)
* numeric modes:                         Numeric Modes.       (line   6)
* numeric operations:                    Numeric operations.  (line   6)
* numeric sequences:                     seq invocation.      (line   6)
* numeric sort:                          sort invocation.     (line 159)
* numeric tests:                         Numeric tests.       (line   6)
* numeric uid and gid:                   What information is listed.
                                                              (line 234)
* numeric user and group IDs:            What information is listed.
                                                              (line 234)
* obs:                                   dd invocation.       (line  29)
* ocrnl:                                 Output.              (line  16)
* octal dump of files:                   od invocation.       (line   6)
* octal numbers for file modes:          Numeric Modes.       (line   6)
* od:                                    od invocation.       (line   6)
* odd parity:                            Control.             (line  13)
* oddp:                                  Combination.         (line  14)
* of:                                    dd invocation.       (line  20)
* ofdel:                                 Output.              (line  34)
* ofill:                                 Output.              (line  30)
* oflag:                                 dd invocation.       (line 162)
* olcuc:                                 Output.              (line  12)
* older-than file check:                 File characteristic tests.
                                                              (line  19)
* once interactive option:               rm invocation.       (line  54)
* one file system, restricting du to:    du invocation.       (line 201)
* one file system, restricting rm to:    rm invocation.       (line  63)
* one-line output format:                df invocation.       (line  85)
* onlcr:                                 Output.              (line  19)
* onlret:                                Output.              (line  27)
* onocr:                                 Output.              (line  23)
* operating on characters:               Operating on characters.
                                                              (line   6)
* operating on sorted files:             Operating on sorted files.
                                                              (line   6)
* operating system name:                 uname invocation.    (line  57)
* opost:                                 Output.              (line   9)
* option delimiter:                      Common options.      (line  44)
* options for date:                      Options for date.    (line   6)
* or operator <1>:                       Relations for expr.  (line  11)
* or operator:                           Connectives for test.
                                                              (line  15)
* ordinal numbers:                       General date syntax. (line  26)
* ospeed:                                Special.             (line  19)
* other permissions:                     Setting Permissions. (line  29)
* output block size:                     dd invocation.       (line  29)
* output file name prefix <1>:           csplit invocation.   (line  62)
* output file name prefix:               split invocation.    (line  14)
* output file name suffix:               csplit invocation.   (line  66)
* output format:                         stat invocation.     (line  33)
* output format, portable:               df invocation.       (line  85)
* output NUL-byte-terminated lines <1>:  env invocation.      (line  83)
* output NUL-byte-terminated lines <2>:  printenv invocation. (line  19)
* output NUL-byte-terminated lines:      du invocation.       (line 122)
* output of entire files:                Output of entire files.
                                                              (line   6)
* output of parts of files:              Output of parts of files.
                                                              (line   6)
* output settings:                       Output.              (line   6)
* output tabs:                           pr invocation.       (line 137)
* overwriting of input, allowed <1>:     shuf invocation.     (line  37)
* overwriting of input, allowed:         sort invocation.     (line 276)
* owned by effective group ID check:     Access permission tests.
                                                              (line  31)
* owned by effective user ID check:      Access permission tests.
                                                              (line  28)
* owner of file, permissions for:        Setting Permissions. (line  23)
* owner, default:                        Mode Structure.      (line  31)
* ownership of installed files, setting: install invocation.  (line  86)
* p for FIFO file:                       mknod invocation.    (line  28)
* pad character:                         Output.              (line  34)
* pad instead of timing for delaying:    Output.              (line  30)
* padding of numeric fields:             Padding and other flags.
                                                              (line   6)
* paragraphs, reformatting:              fmt invocation.      (line   6)
* parenb:                                Control.             (line   9)
* parent directories and cp:             cp invocation.       (line 240)
* parent directories, creating:          mkdir invocation.    (line  39)
* parent directories, creating missing:  install invocation.  (line  62)
* parent directories, removing:          rmdir invocation.    (line  22)
* parentheses for grouping:              expr invocation.     (line  31)
* parity:                                Combination.         (line  10)
* parity errors, marking:                Input.               (line  18)
* parity, ignoring:                      Input.               (line  15)
* parmrk:                                Input.               (line  18)
* parodd:                                Control.             (line  13)
* parsing date strings:                  Options for date.    (line  11)
* parts of files, output of:             Output of parts of files.
                                                              (line   6)
* pass8:                                 Combination.         (line  55)
* passwd entry, and su shell:            su invocation.       (line  14)
* paste:                                 paste invocation.    (line   6)
* Paterson, R.:                          Introduction.        (line  19)
* PATH <1>:                              su invocation.       (line  57)
* PATH:                                  env invocation.      (line  23)
* pathchk:                               pathchk invocation.  (line   6)
* pattern matching:                      String expressions.  (line  11)
* PC file system:                        df invocation.       (line 144)
* pcfs:                                  df invocation.       (line 144)
* pebibyte, definition of:               Block size.          (line 113)
* permission tests:                      Access permission tests.
                                                              (line   6)
* permissions of installed files, setting: install invocation.
                                                              (line  74)
* permissions, changing access:          chmod invocation.    (line   6)
* permissions, copying existing:         Copying Permissions. (line   6)
* permissions, for changing file timestamps: touch invocation.
                                                              (line  17)
* permissions, output by ls:             What information is listed.
                                                              (line 191)
* petabyte, definition of:               Block size.          (line 109)
* phone directory order:                 sort invocation.     (line  87)
* pieces, splitting a file into:         split invocation.    (line   6)
* Pinard, F. <1>:                        Authors of get_date. (line  14)
* Pinard, F.:                            Introduction.        (line  19)
* pipe fitting:                          tee invocation.      (line   6)
* Plass, Michael F.:                     fmt invocation.      (line  19)
* platform, hardware:                    uname invocation.    (line  35)
* pm in date strings:                    Time of day items.   (line  22)
* portable file names, checking for:     pathchk invocation.  (line   6)
* portable output format:                df invocation.       (line  85)
* POSIX:                                 Introduction.        (line  11)
* POSIX output format:                   df invocation.       (line  85)
* POSIXLY_CORRECT <1>:                   id invocation.       (line  11)
* POSIXLY_CORRECT <2>:                   printf invocation.   (line  50)
* POSIXLY_CORRECT <3>:                   echo invocation.     (line  78)
* POSIXLY_CORRECT <4>:                   dd invocation.       (line 292)
* POSIXLY_CORRECT <5>:                   sort invocation.     (line 284)
* POSIXLY_CORRECT <6>:                   pr invocation.       (line 105)
* POSIXLY_CORRECT <7>:                   Standards conformance.
                                                              (line   6)
* POSIXLY_CORRECT:                       Common options.      (line  11)
* POSIXLY_CORRECT, and block size:       Block size.          (line  12)
* pr:                                    pr invocation.       (line   6)
* prime factors:                         factor invocation.   (line   6)
* print:                                 Character sets.      (line 113)
* print machine hardware name:           arch invocation.     (line   6)
* print name of current directory:       pwd invocation.      (line   6)
* print system information:              uname invocation.    (line   6)
* print terminal file name:              tty invocation.      (line   6)
* Print the number of processors:        nproc invocation.    (line   6)
* printenv:                              printenv invocation. (line   6)
* printf:                                printf invocation.   (line   6)
* printing all or some environment variables: printenv invocation.
                                                              (line   6)
* printing color database:               dircolors invocation.
                                                              (line  45)
* printing current user information:     who invocation.      (line   6)
* printing current usernames:            users invocation.    (line   6)
* printing groups a user is in:          groups invocation.   (line   6)
* printing real and effective user and group IDs: id invocation.
                                                              (line   6)
* printing text:                         echo invocation.     (line   6)
* printing text, commands for:           Printing text.       (line   6)
* printing the current time:             date invocation.     (line   6)
* printing the effective user ID:        whoami invocation.   (line   6)
* printing the host identifier:          hostid invocation.   (line   6)
* printing the hostname:                 hostname invocation. (line   6)
* printing the system uptime and load:   uptime invocation.   (line   6)
* printing user's login name:            logname invocation.  (line   6)
* printing, preparing files for:         pr invocation.       (line   6)
* process zero-terminated items <1>:     uniq invocation.     (line 112)
* process zero-terminated items <2>:     shuf invocation.     (line  48)
* process zero-terminated items:         sort invocation.     (line 359)
* processes, commands for controlling:   Process control.     (line   6)
* prompting, and ln:                     ln invocation.       (line 100)
* prompting, and mv:                     mv invocation.       (line  36)
* prompting, and rm:                     rm invocation.       (line  11)
* prompts, forcing:                      mv invocation.       (line  67)
* prompts, omitting:                     mv invocation.       (line  61)
* prterase:                              Local.               (line  46)
* ptx:                                   ptx invocation.      (line   6)
* punct:                                 Character sets.      (line 116)
* pure numbers in date strings:          Pure numbers in date strings.
                                                              (line   6)
* pwd:                                   pwd invocation.      (line   6)
* quit:                                  Characters.          (line  23)
* quoting style:                         Formatting the file names.
                                                              (line  34)
* radix for file offsets:                od invocation.       (line  36)
* random sort:                           sort invocation.     (line 188)
* random source for shredding:           shred invocation.    (line 112)
* random source for shuffling:           shuf invocation.     (line  43)
* random source for sorting:             sort invocation.     (line 289)
* random sources:                        Random sources.      (line   6)
* ranges:                                Character sets.      (line  51)
* raw:                                   Combination.         (line  43)
* read errors, ignoring:                 dd invocation.       (line 128)
* read from stdin and write to stdout and files: tee invocation.
                                                              (line   6)
* read permission:                       Mode Structure.      (line  12)
* read permission, symbolic:             Setting Permissions. (line  57)
* read system call, and holes:           cp invocation.       (line 289)
* readable file check:                   Access permission tests.
                                                              (line  15)
* readlink:                              readlink invocation. (line   6)
* real user and group IDs, printing:     id invocation.       (line   6)
* realpath:                              readlink invocation. (line   6)
* recursive directory listing:           Which files are listed.
                                                              (line  91)
* recursively changing access permissions: chmod invocation.  (line  69)
* recursively changing file ownership:   chown invocation.    (line 140)
* recursively changing group ownership:  chgrp invocation.    (line  66)
* recursively copying directories:       cp invocation.       (line  95)
* redirection:                           Redirection.         (line   6)
* reference file:                        chcon invocation.    (line  25)
* reformatting paragraph text:           fmt invocation.      (line   6)
* regular expression matching:           String expressions.  (line  11)
* regular file check:                    File type tests.     (line  19)
* relations, numeric or string:          Relations for expr.  (line   6)
* relative items in date strings:        Relative items in date strings.
                                                              (line   6)
* release of kernel:                     uname invocation.    (line  61)
* remainder:                             Numeric expressions. (line  16)
* remote hostname:                       who invocation.      (line  11)
* removing empty directories:            rmdir invocation.    (line   6)
* removing files after shredding:        shred invocation.    (line 123)
* removing files or directories:         rm invocation.       (line   6)
* removing files or directories (via the unlink syscall): unlink invocation.
                                                              (line   6)
* removing permissions:                  Setting Permissions. (line  42)
* repeated characters:                   Character sets.      (line  72)
* repeated lines, outputting:            uniq invocation.     (line  63)
* repeated output of a string:           yes invocation.      (line   6)
* restricted deletion flag:              Mode Structure.      (line  56)
* restricted shell:                      su invocation.       (line  69)
* return, ignoring:                      Input.               (line  31)
* return, translating to newline <1>:    Output.              (line  16)
* return, translating to newline:        Input.               (line  34)
* reverse sorting <1>:                   Sorting the output.  (line  27)
* reverse sorting:                       sort invocation.     (line 182)
* reversing files:                       tac invocation.      (line   6)
* rm:                                    rm invocation.       (line   6)
* rmdir:                                 rmdir invocation.    (line   6)
* rn format for nl:                      nl invocation.       (line 101)
* root as default owner:                 install invocation.  (line  86)
* root directory, allow recursive destruction: rm invocation. (line  84)
* root directory, allow recursive modification <1>: chmod invocation.
                                                              (line  54)
* root directory, allow recursive modification <2>: chgrp invocation.
                                                              (line  48)
* root directory, allow recursive modification: chown invocation.
                                                              (line 121)
* root directory, disallow recursive destruction: rm invocation.
                                                              (line  79)
* root directory, disallow recursive modification <1>: chmod invocation.
                                                              (line  49)
* root directory, disallow recursive modification <2>: chgrp invocation.
                                                              (line  43)
* root directory, disallow recursive modification: chown invocation.
                                                              (line 116)
* root directory, running a program in a specified: chroot invocation.
                                                              (line   6)
* root, becoming:                        su invocation.       (line   6)
* rows:                                  Special.             (line  22)
* rprnt:                                 Characters.          (line  56)
* RTS/CTS flow control:                  Control.             (line  36)
* run commands with bounded time:        timeout invocation.  (line   6)
* run with security context:             runcon invocation.   (line   6)
* runcon:                                runcon invocation.   (line   6)
* running a program in a modified environment: env invocation.
                                                              (line   6)
* running a program in a specified root directory: chroot invocation.
                                                              (line   6)
* rz format for nl:                      nl invocation.       (line 104)
* Salz, Rich:                            Authors of get_date. (line   6)
* same file check:                       File characteristic tests.
                                                              (line  23)
* sane:                                  Combination.         (line  26)
* scheduling, affecting:                 nice invocation.     (line   6)
* screen columns:                        fold invocation.     (line  14)
* seconds since the epoch:               Time conversion specifiers.
                                                              (line  41)
* section delimiters of pages:           nl invocation.       (line  68)
* security context <1>:                  id invocation.       (line  48)
* security context <2>:                  mknod invocation.    (line  57)
* security context <3>:                  mkfifo invocation.   (line  30)
* security context <4>:                  mkdir invocation.    (line  65)
* security context <5>:                  install invocation.  (line  91)
* security context:                      What information is listed.
                                                              (line 268)
* seek:                                  dd invocation.       (line  48)
* self-backups:                          cp invocation.       (line  53)
* SELinux <1>:                           id invocation.       (line  48)
* SELinux <2>:                           mknod invocation.    (line  57)
* SELinux <3>:                           mkfifo invocation.   (line  30)
* SELinux <4>:                           mkdir invocation.    (line  65)
* SELinux <5>:                           install invocation.  (line  91)
* SELinux:                               What information is listed.
                                                              (line 268)
* SELinux context:                       SELinux context.     (line   6)
* SELinux security context information, preserving: cp invocation.
                                                              (line  90)
* SELinux, context:                      SELinux context.     (line   6)
* send a signal to processes:            kill invocation.     (line   6)
* sentences and line-breaking:           fmt invocation.      (line  19)
* separator for numbers in seq:          seq invocation.      (line  42)
* seq:                                   seq invocation.      (line   6)
* sequence of numbers:                   seq invocation.      (line   6)
* set-group-ID:                          Mode Structure.      (line  49)
* set-group-ID check:                    Access permission tests.
                                                              (line   9)
* set-user-ID:                           Mode Structure.      (line  42)
* set-user-ID check:                     Access permission tests.
                                                              (line  18)
* setgid:                                Mode Structure.      (line  49)
* setting permissions:                   Setting Permissions. (line  46)
* setting the hostname:                  hostname invocation. (line   6)
* setting the time:                      Setting the time.    (line   6)
* setuid:                                Mode Structure.      (line  42)
* setup for color:                       dircolors invocation.
                                                              (line   6)
* sh syntax for color setup:             dircolors invocation.
                                                              (line  34)
* SHA-1:                                 sha1sum invocation.  (line   6)
* SHA-2:                                 sha2 utilities.      (line   6)
* sha1sum:                               sha1sum invocation.  (line   6)
* sha224sum:                             sha2 utilities.      (line   6)
* sha256sum:                             sha2 utilities.      (line   6)
* sha384sum:                             sha2 utilities.      (line   6)
* sha512sum:                             sha2 utilities.      (line   6)
* SHELL:                                 su invocation.       (line  20)
* SHELL environment variable, and color: dircolors invocation.
                                                              (line  23)
* shell utilities:                       Top.                 (line  18)
* shred:                                 shred invocation.    (line   6)
* shuf:                                  shuf invocation.     (line   6)
* shuffling files:                       shuf invocation.     (line   6)
* SI output <1>:                         du invocation.       (line 128)
* SI output <2>:                         df invocation.       (line 104)
* SI output <3>:                         What information is listed.
                                                              (line 260)
* SI output:                             Block size.          (line  43)
* signals, specifying:                   Signal specifications.
                                                              (line   6)
* simple backup method:                  Backup options.      (line  44)
* SIMPLE_BACKUP_SUFFIX:                  Backup options.      (line  50)
* single-column output of files:         General output formatting.
                                                              (line  10)
* size:                                  Special.             (line  30)
* size for main memory sorting:          sort invocation.     (line 300)
* size of file to shred:                 shred invocation.    (line 117)
* size of files, reporting:              What information is listed.
                                                              (line 244)
* size of files, sorting files by:       Sorting the output.  (line  32)
* skip:                                  dd invocation.       (line  45)
* sleep:                                 sleep invocation.    (line   6)
* socket check:                          File type tests.     (line  31)
* software flow control:                 Input.               (line  45)
* sort:                                  sort invocation.     (line   6)
* sort field:                            sort invocation.     (line 231)
* sort stability:                        sort invocation.     (line  38)
* sort's last-resort comparison:         sort invocation.     (line  38)
* sorted files, operations on:           Operating on sorted files.
                                                              (line   6)
* sorting files:                         sort invocation.     (line   6)
* sorting ls output:                     Sorting the output.  (line   6)
* space:                                 Character sets.      (line 119)
* sparse:                                dd invocation.       (line 113)
* sparse files, copying:                 cp invocation.       (line 289)
* sparse files, creating:                truncate invocation. (line  13)
* special characters:                    Characters.          (line   6)
* special file types:                    Special file types.  (line   6)
* special files:                         mknod invocation.    (line  11)
* special settings:                      Special.             (line   6)
* specifying sets of characters:         Character sets.      (line   6)
* speed:                                 Special.             (line  40)
* split:                                 split invocation.    (line   6)
* splitting a file into pieces:          split invocation.    (line   6)
* splitting a file into pieces by context: csplit invocation. (line   6)
* squeezing empty lines:                 cat invocation.      (line  35)
* squeezing repeat characters:           Squeezing.           (line   6)
* Stallman, R.:                          Introduction.        (line  19)
* standard input:                        Common options.      (line  49)
* standard output:                       Common options.      (line  49)
* standard streams, buffering:           stdbuf invocation.   (line   6)
* start:                                 Characters.          (line  44)
* stat:                                  stat invocation.     (line   6)
* status:                                dd invocation.       (line  57)
* status time, printing or sorting by:   Sorting the output.  (line  13)
* status time, show the most recent:     du invocation.       (line 154)
* stdbuf:                                stdbuf invocation.   (line   6)
* sticky:                                Mode Structure.      (line  56)
* sticky bit check:                      Access permission tests.
                                                              (line  12)
* stop:                                  Characters.          (line  47)
* stop bits:                             Control.             (line  27)
* strftime and date:                     date invocation.     (line  20)
* string constants, outputting:          od invocation.       (line  76)
* string expressions:                    String expressions.  (line   6)
* string tests:                          String tests.        (line   6)
* strip directory and suffix from file names: basename invocation.
                                                              (line   6)
* stripping non-directory suffix:        dirname invocation.  (line   6)
* stripping symbol table information:    install invocation.  (line 108)
* stripping trailing slashes <1>:        mv invocation.       (line  93)
* stripping trailing slashes:            cp invocation.       (line 323)
* stty:                                  stty invocation.     (line   6)
* su:                                    su invocation.       (line   6)
* substitute user and group IDs:         su invocation.       (line   6)
* substr:                                String expressions.  (line  40)
* subtracting permissions:               Setting Permissions. (line  42)
* subtraction:                           Numeric expressions. (line  12)
* successful exit:                       true invocation.     (line   6)
* suffix, stripping from file names:     basename invocation. (line   6)
* sum:                                   sum invocation.      (line   6)
* summarizing files:                     Summarizing files.   (line   6)
* super-user, becoming:                  su invocation.       (line   6)
* superblock, writing:                   sync invocation.     (line   6)
* supplementary groups, printing:        groups invocation.   (line   6)
* susp:                                  Characters.          (line  50)
* swab (byte-swapping):                  dd invocation.       (line 123)
* swap space, saving text image in:      Mode Structure.      (line  56)
* swtch:                                 Characters.          (line  41)
* symbol table information, stripping:   install invocation.  (line 108)
* symbol table information, stripping, program: install invocation.
                                                              (line 111)
* symbolic (soft) links, creating:       ln invocation.       (line   6)
* symbolic link check:                   File type tests.     (line  23)
* symbolic link to directory, controlling traversal of: Traversing symlinks.
                                                              (line   6)
* symbolic link to directory, never traverse <1>: chcon invocation.
                                                              (line  42)
* symbolic link to directory, never traverse <2>: chgrp invocation.
                                                              (line  79)
* symbolic link to directory, never traverse <3>: chown invocation.
                                                              (line 152)
* symbolic link to directory, never traverse: Traversing symlinks.
                                                              (line  26)
* symbolic link to directory, traverse each that is encountered <1>: chcon invocation.
                                                              (line  38)
* symbolic link to directory, traverse each that is encountered <2>: chgrp invocation.
                                                              (line  75)
* symbolic link to directory, traverse each that is encountered <3>: chown invocation.
                                                              (line 148)
* symbolic link to directory, traverse each that is encountered: Traversing symlinks.
                                                              (line  22)
* symbolic link to directory, traverse each that is specified on the command line <1>: chcon invocation.
                                                              (line  33)
* symbolic link to directory, traverse each that is specified on the command line <2>: chgrp invocation.
                                                              (line  70)
* symbolic link to directory, traverse each that is specified on the command line <3>: chown invocation.
                                                              (line 143)
* symbolic link to directory, traverse each that is specified on the command line: Traversing symlinks.
                                                              (line  18)
* symbolic link, defined:                ln invocation.       (line  42)
* symbolic links and ln:                 ln invocation.       (line 161)
* symbolic links and pwd:                pwd invocation.      (line  26)
* symbolic links, changing group:        chgrp invocation.    (line  35)
* symbolic links, changing owner <1>:    chgrp invocation.    (line  30)
* symbolic links, changing owner:        chown invocation.    (line  80)
* symbolic links, changing time:         touch invocation.    (line  75)
* symbolic links, copying:               cp invocation.       (line 108)
* symbolic links, copying with:          cp invocation.       (line 328)
* symbolic links, dereferencing:         Which files are listed.
                                                              (line  36)
* symbolic links, dereferencing in du:   du invocation.       (line 101)
* symbolic links, dereferencing in stat: stat invocation.     (line  22)
* symbolic links, following:             dd invocation.       (line 224)
* symbolic links, permissions of:        chmod invocation.    (line  10)
* symbolic modes:                        Symbolic Modes.      (line   6)
* sync <1>:                              sync invocation.     (line   6)
* sync:                                  dd invocation.       (line 207)
* sync (padding with ASCII NULs):        dd invocation.       (line 144)
* synchronize disk and memory:           sync invocation.     (line   6)
* synchronized data and metadata I/O:    dd invocation.       (line 207)
* synchronized data and metadata writes, before finishing: dd invocation.
                                                              (line 153)
* synchronized data reads:               dd invocation.       (line 199)
* synchronized data writes, before finishing: dd invocation.  (line 149)
* syslog:                                su invocation.       (line  31)
* system context:                        System context.      (line   6)
* system information, printing <1>:      uname invocation.    (line   6)
* system information, printing <2>:      nproc invocation.    (line   6)
* system information, printing:          arch invocation.     (line   6)
* system name, printing:                 hostname invocation. (line   6)
* System V sum:                          sum invocation.      (line  31)
* tab stops, setting:                    expand invocation.   (line  22)
* tabN:                                  Output.              (line  51)
* tabs:                                  Combination.         (line  66)
* tabs to spaces, converting:            expand invocation.   (line   6)
* tac:                                   tac invocation.      (line   6)
* tagged paragraphs:                     fmt invocation.      (line  40)
* tail:                                  tail invocation.     (line   6)
* tandem:                                Input.               (line  45)
* target directory <1>:                  ln invocation.       (line 149)
* target directory <2>:                  mv invocation.       (line 103)
* target directory <3>:                  install invocation.  (line 120)
* target directory <4>:                  cp invocation.       (line 341)
* target directory:                      Target directory.    (line   6)
* tebibyte, definition of:               Block size.          (line 106)
* tee:                                   tee invocation.      (line   6)
* telephone directory order:             sort invocation.     (line  87)
* temporary directory:                   sort invocation.     (line 336)
* temporary files and directories:       mktemp invocation.   (line   6)
* terabyte, definition of:               Block size.          (line 102)
* TERM:                                  su invocation.       (line  57)
* terminal check:                        File type tests.     (line  34)
* terminal file name, printing:          tty invocation.      (line   6)
* terminal lines, currently used:        who invocation.      (line  11)
* terminal settings:                     stty invocation.     (line   6)
* terminal, using color iff:             General output formatting.
                                                              (line  25)
* terse output:                          stat invocation.     (line  53)
* test:                                  test invocation.     (line   6)
* text:                                  dd invocation.       (line 234)
* text I/O:                              dd invocation.       (line 234)
* text image, saving in swap space:      Mode Structure.      (line  56)
* text input files:                      md5sum invocation.   (line  87)
* text utilities:                        Top.                 (line  18)
* text, displaying:                      echo invocation.     (line   6)
* text, reformatting:                    fmt invocation.      (line   6)
* this in date strings:                  Relative items in date strings.
                                                              (line  33)
* time <1>:                              Special.             (line  11)
* time:                                  touch invocation.    (line  61)
* time conversion specifiers:            Time conversion specifiers.
                                                              (line   6)
* time formats <1>:                      date invocation.     (line  20)
* time formats:                          pr invocation.       (line  98)
* time limit:                            timeout invocation.  (line   6)
* time of day item:                      Time of day items.   (line   6)
* time setting:                          Setting the time.    (line   6)
* time style <1>:                        du invocation.       (line 163)
* time style:                            Formatting file timestamps.
                                                              (line  26)
* time units <1>:                        sleep invocation.    (line  11)
* time units:                            timeout invocation.  (line  11)
* time zone correction:                  Time of day items.   (line  30)
* time zone item <1>:                    Time zone items.     (line   6)
* time zone item:                        General date syntax. (line  44)
* time, printing or setting:             date invocation.     (line   6)
* TIME_STYLE <1>:                        du invocation.       (line 191)
* TIME_STYLE:                            Formatting file timestamps.
                                                              (line 106)
* timeout:                               timeout invocation.  (line   6)
* timestamps of installed files, preserving: install invocation.
                                                              (line  98)
* timestamps, changing file:             touch invocation.    (line   6)
* TMPDIR:                                sort invocation.     (line  64)
* today in date strings:                 Relative items in date strings.
                                                              (line  33)
* tomorrow:                              Options for date.    (line  11)
* tomorrow in date strings:              Relative items in date strings.
                                                              (line  29)
* topological sort:                      tsort invocation.    (line   6)
* tostop:                                Local.               (line  41)
* total counts:                          wc invocation.       (line  12)
* touch:                                 touch invocation.    (line   6)
* tr:                                    tr invocation.       (line   6)
* trailing slashes:                      Trailing slashes.    (line   6)
* translating characters:                Translating.         (line   6)
* true:                                  true invocation.     (line   6)
* truncate:                              truncate invocation. (line   6)
* truncating output file, avoiding:      dd invocation.       (line 141)
* truncating, file sizes:                truncate invocation. (line   6)
* tsort:                                 tsort invocation.    (line   6)
* tty:                                   tty invocation.      (line   6)
* two-way parity:                        Control.             (line   9)
* type size:                             od invocation.       (line 122)
* TZ <1>:                                Specifying time zone rules.
                                                              (line   6)
* TZ <2>:                                Options for date.    (line  87)
* TZ <3>:                                date invocation.     (line  16)
* TZ <4>:                                who invocation.      (line  26)
* TZ <5>:                                stat invocation.     (line 139)
* TZ <6>:                                touch invocation.    (line  40)
* TZ <7>:                                Formatting file timestamps.
                                                              (line  18)
* TZ:                                    pr invocation.       (line 111)
* u, and disabling special characters:   Characters.          (line  13)
* ucase, converting to:                  dd invocation.       (line 108)
* ufs file system type:                  df invocation.       (line 136)
* umask and modes:                       Umask and Protection.
                                                              (line   6)
* uname:                                 uname invocation.    (line   6)
* unblock:                               dd invocation.       (line  99)
* unexpand:                              unexpand invocation. (line   6)
* Unicode:                               printf invocation.   (line  72)
* uniq:                                  uniq invocation.     (line   6)
* unique lines, outputting:              uniq invocation.     (line 101)
* uniquify files:                        uniq invocation.     (line   6)
* uniquifying output:                    sort invocation.     (line 345)
* unlink:                                unlink invocation.   (line   6)
* unprintable characters, ignoring:      sort invocation.     (line 142)
* unsorted directory listing:            Sorting the output.  (line  20)
* upper:                                 Character sets.      (line 122)
* uppercase, translating to lowercase:   Input.               (line  50)
* uptime:                                uptime invocation.   (line   6)
* use time, changing:                    touch invocation.    (line  53)
* use time, printing or sorting files by: Sorting the output. (line  13)
* use time, show the most recent:        du invocation.       (line 154)
* USER:                                  su invocation.       (line  20)
* user ID, switching:                    su invocation.       (line   6)
* user IDs, disambiguating:              Disambiguating names and IDs.
                                                              (line   6)
* user information, commands for:        User information.    (line   6)
* user name, printing:                   logname invocation.  (line   6)
* user names, disambiguating:            Disambiguating names and IDs.
                                                              (line   6)
* usernames, printing current:           users invocation.    (line   6)
* users:                                 users invocation.    (line   6)
* UTC:                                   Options for date.    (line  87)
* utmp <1>:                              who invocation.      (line  15)
* utmp <2>:                              users invocation.    (line  14)
* utmp:                                  logname invocation.  (line   6)
* valid file names, checking for:        pathchk invocation.  (line   6)
* variable-length records, converting to fixed-length: dd invocation.
                                                              (line  40)
* vdir:                                  vdir invocation.     (line   6)
* verbose ls format:                     What information is listed.
                                                              (line 131)
* verifying MD5 checksums:               md5sum invocation.   (line  69)
* version number sort:                   sort invocation.     (line 176)
* version number, finding:               Common options.      (line  41)
* version of kernel:                     uname invocation.    (line  76)
* version, sorting option for ls:        Sorting the output.  (line  56)
* version-control Emacs variable:        Backup options.      (line  24)
* VERSION_CONTROL <1>:                   ln invocation.       (line  84)
* VERSION_CONTROL <2>:                   mv invocation.       (line  56)
* VERSION_CONTROL <3>:                   install invocation.  (line  42)
* VERSION_CONTROL <4>:                   cp invocation.       (line  75)
* VERSION_CONTROL:                       Backup options.      (line  13)
* vertical sorted files in columns:      General output formatting.
                                                              (line  15)
* vtN:                                   Output.              (line  59)
* wc:                                    wc invocation.       (line   6)
* week in date strings:                  Relative items in date strings.
                                                              (line  15)
* werase:                                Characters.          (line  59)
* who:                                   who invocation.      (line   6)
* who am i:                              who invocation.      (line  21)
* whoami:                                whoami invocation.   (line   6)
* word count:                            wc invocation.       (line   6)
* working context:                       Working context.     (line   6)
* working directory, printing:           pwd invocation.      (line   6)
* wrap data:                             base64 invocation.   (line  22)
* wrapping long input lines:             fold invocation.     (line   6)
* writable file check:                   Access permission tests.
                                                              (line  21)
* write permission:                      Mode Structure.      (line  15)
* write permission, symbolic:            Setting Permissions. (line  60)
* write, allowed:                        who invocation.      (line  95)
* wtmp <1>:                              who invocation.      (line  15)
* wtmp:                                  users invocation.    (line  14)
* xcase:                                 Local.               (line  36)
* xdigit:                                Character sets.      (line 125)
* XON/XOFF flow control:                 Input.               (line  40)
* year in date strings:                  Relative items in date strings.
                                                              (line  15)
* yes:                                   yes invocation.      (line   6)
* yesterday:                             Options for date.    (line  11)
* yesterday in date strings:             Relative items in date strings.
                                                              (line  29)
* yottabyte, definition of:              Block size.          (line 131)
* Youmans, B.:                           Introduction.        (line  19)
* zero-length string check:              String tests.        (line  15)
* zettabyte, definition of:              Block size.          (line 123)
* |:                                     Relations for expr.  (line  11)



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