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GAWK(1)                        Utility Commands                        GAWK(1)



NAME
       gawk - pattern scanning and processing language

SYNOPSIS
       gawk [ POSIX or GNU style options ] -f program-file [ -- ] file ...
       gawk [ POSIX or GNU style options ] [ -- ] program-text file ...

       pgawk [ POSIX or GNU style options ] -f program-file [ -- ] file ...
       pgawk [ POSIX or GNU style options ] [ -- ] program-text file ...

DESCRIPTION
       Gawk  is the GNU Project's implementation of the AWK programming language.  It con-
       forms to the definition of the language in the POSIX 1003.1 Standard.  This version
       in  turn  is  based  on  the  description  in The AWK Programming Language, by Aho,
       Kernighan, and Weinberger, with the additional  features  found  in  the  System  V
       Release  4  version  of UNIX awk.  Gawk also provides more recent Bell Laboratories
       awk extensions, and a number of GNU-specific extensions.

       Pgawk is the profiling version of gawk.  It is identical  in  every  way  to  gawk,
       except  that  programs  run more slowly, and it automatically produces an execution
       profile in the file awkprof.out when done.  See the --profile option, below.

       The command line consists of options to gawk itself, the AWK program text  (if  not
       supplied via the -f or --file options), and values to be made available in the ARGC
       and ARGV pre-defined AWK variables.

OPTION FORMAT
       Gawk options may be either traditional POSIX one letter options, or GNU-style  long
       options.   POSIX  options  start  with  a single "-", while long options start with
       "--".  Long options are provided for both GNU-specific features and for  POSIX-man-
       dated features.

       Following  the  POSIX standard, gawk-specific options are supplied via arguments to
       the -W option.  Multiple -W options may be supplied Each -W  option  has  a  corre-
       sponding  long  option,  as  detailed  below.  Arguments to long options are either
       joined with the option by an = sign, with no intervening spaces,  or  they  may  be
       provided  in  the  next command line argument.  Long options may be abbreviated, as
       long as the abbreviation remains unique.

OPTIONS
       Gawk accepts the following options, listed by frequency.

       -F fs
       --field-separator fs
              Use fs for the input field separator (the value of the FS  predefined  vari-
              able).

       -v var=val
       --assign var=val
              Assign  the  value  val to the variable var, before execution of the program
              begins.  Such variable values are available to the BEGIN  block  of  an  AWK
              program.

       -f program-file
       --file program-file
              Read  the AWK program source from the file program-file, instead of from the
              first command line argument.  Multiple -f (or --file) options may be used.

       -mf NNN
       -mr NNN
              Set various memory limits to the value NNN.  The f  flag  sets  the  maximum
              number  of  fields,  and the r flag sets the maximum record size.  These two
              flags and the -m option are from an earlier version of the Bell Laboratories
              research  version  of UNIX awk.  They are ignored by gawk, since gawk has no
              pre-defined limits.  (Current versions  of  the  Bell  Laboratories  awk  no
              longer accept them.)

       -O
       --optimize
              Enable  optimizations upon the internal representation of the program.  Cur-
              rently, this includes just  simple  constant-folding.  The  gawk  maintainer
              hopes to add additional optimizations over time.

       -W compat
       -W traditional
       --compat
       --traditional
              Run  in compatibility mode.  In compatibility mode, gawk behaves identically
              to UNIX awk; none of the GNU-specific extensions are recognized.  The use of
              --traditional  is  preferred  over  the other forms of this option.  See GNU
              EXTENSIONS, below, for more information.

       -W copyleft
       -W copyright
       --copyleft
       --copyright
              Print the short version of the GNU  copyright  information  message  on  the
              standard output and exit successfully.

       -W dump-variables[=file]
       --dump-variables[=file]
              Print  a  sorted  list  of global variables, their types and final values to
              file.  If no file is provided, gawk uses a file  named  awkvars.out  in  the
              current directory.
              Having  a  list  of all the global variables is a good way to look for typo-
              graphical errors in your programs.  You would also use this  option  if  you
              have  a  large program with a lot of functions, and you want to be sure that
              your functions don't inadvertently use global variables that you meant to be
              local.   (This  is  a particularly easy mistake to make with simple variable
              names like i, j, and so on.)

       -W exec file
       --exec file
              Similar to -f, however, this is option is  the  last  one  processed.   This
              should be used with #!  scripts, particularly for CGI applications, to avoid
              passing in options or source code (!) on the command line from a URL.   This
              option disables command-line variable assignments.

       -W gen-po
       --gen-po
              Scan  and parse the AWK program, and generate a GNU .po format file on stan-
              dard output with entries for all localizable strings in  the  program.   The
              program  itself  is not executed.  See the GNU gettext distribution for more
              information on .po files.

       -W help
       -W usage
       --help
       --usage
              Print a relatively short summary of the available options  on  the  standard
              output.   (Per  the  GNU Coding Standards, these options cause an immediate,
              successful exit.)

       -W lint[=value]
       --lint[=value]
              Provide warnings about constructs that are dubious or non-portable to  other
              AWK  implementations.   With  an  optional  argument of fatal, lint warnings
              become fatal errors.  This may  be  drastic,  but  its  use  will  certainly
              encourage  the  development of cleaner AWK programs.  With an optional argu-
              ment of invalid, only warnings about things that are  actually  invalid  are
              issued. (This is not fully implemented yet.)

       -W lint-old
       --lint-old
              Provide warnings about constructs that are not portable to the original ver-
              sion of Unix awk.

       -W non-decimal-data
       --non-decimal-data
              Recognize octal and hexadecimal values in input data.  Use this option  with
              great caution!

       -W posix
       --posix
              This  turns  on  compatibility  mode, with the following additional restric-
              tions:

              ? \x escape sequences are not recognized.

              ? Only space and tab act as field separators when FS  is  set  to  a  single
                space, newline does not.

              ? You cannot continue lines after ?  and :.

              ? The synonym func for the keyword function is not recognized.

              ? The operators ** and **= cannot be used in place of ^ and ^=.

              ? The fflush() function is not available.

       -W profile[=prof_file]
       --profile[=prof_file]
              Send  profiling  data  to  prof_file.  The default is awkprof.out.  When run
              with gawk, the profile is just a "pretty printed" version  of  the  program.
              When run with pgawk, the profile contains execution counts of each statement
              in the program in the left margin and function call counts  for  each  user-
              defined function.

       -W re-interval
       --re-interval
              Enable  the  use of interval expressions in regular expression matching (see
              Regular Expressions, below).  Interval expressions  were  not  traditionally
              available  in  the AWK language.  The POSIX standard added them, to make awk
              and egrep consistent with each other.  However, their use is likely to break
              old AWK programs, so gawk only provides them if they are requested with this
              option, or when --posix is specified.

       -W source program-text
       --source program-text
              Use program-text as AWK program source code.  This option  allows  the  easy
              intermixing  of  library functions (used via the -f and --file options) with
              source code entered on the command  line.   It  is  intended  primarily  for
              medium to large AWK programs used in shell scripts.

       -W use-lc-numeric
       --use-lc-numeric
              This  forces  gawk  to use the locale's decimal point character when parsing
              input data.  Although the POSIX standard requires this  behavior,  and  gawk
              does  so  when  --posix  is  in effect, the default is to follow traditional
              behavior and use a period as the decimal point, even in  locales  where  the
              period  is  not  the  decimal  point  character.   This option overrides the
              default behavior, without the  full  draconian  strictness  of  the  --posix
              option.

       -W version
       --version
              Print  version  information for this particular copy of gawk on the standard
              output.  This is useful mainly for knowing if the current copy  of  gawk  on
              your system is up to date with respect to whatever the Free Software Founda-
              tion is distributing.  This is also useful when reporting  bugs.   (Per  the
              GNU Coding Standards, these options cause an immediate, successful exit.)

       --     Signal  the end of options. This is useful to allow further arguments to the
              AWK program itself to start with a "-".  This provides consistency with  the
              argument parsing convention used by most other POSIX programs.

       In  compatibility mode, any other options are flagged as invalid, but are otherwise
       ignored.  In normal operation, as long as program text has been  supplied,  unknown
       options are passed on to the AWK program in the ARGV array for processing.  This is
       particularly useful for running AWK programs via the  "#!"  executable  interpreter
       mechanism.

AWK PROGRAM EXECUTION
       An  AWK  program  consists  of a sequence of pattern-action statements and optional
       function definitions.

              pattern   { action statements }
              function name(parameter list) { statements }

       Gawk first reads the program source from the  program-file(s)  if  specified,  from
       arguments  to  --source, or from the first non-option argument on the command line.
       The -f and --source options may be used multiple times on the command  line.   Gawk
       reads  the  program  text as if all the program-files and command line source texts
       had been concatenated together.  This is useful for building libraries of AWK func-
       tions,  without  having to include them in each new AWK program that uses them.  It
       also provides the ability to mix library functions with command line programs.

       The environment variable AWKPATH specifies a search path to use when finding source
       files  named with the -f option.  If this variable does not exist, the default path
       is ".:/usr/local/share/awk".  (The actual directory may vary,  depending  upon  how
       gawk  was  built  and installed.)  If a file name given to the -f option contains a
       "/" character, no path search is performed.

       Gawk executes AWK programs in the following order.  First, all variable assignments
       specified via the -v option are performed.  Next, gawk compiles the program into an
       internal form.  Then, gawk executes the code in the BEGIN block(s)  (if  any),  and
       then  proceeds  to  read  each file named in the ARGV array.  If there are no files
       named on the command line, gawk reads the standard input.

       If a filename on the command line has the form var=val it is treated as a  variable
       assignment.   The variable var will be assigned the value val.  (This happens after
       any BEGIN block(s) have been run.)  Command line variable assignment is most useful
       for  dynamically assigning values to the variables AWK uses to control how input is
       broken into fields and records.  It is also useful for controlling state if  multi-
       ple passes are needed over a single data file.

       If the value of a particular element of ARGV is empty (""), gawk skips over it.

       For  each  record  in the input, gawk tests to see if it matches any pattern in the
       AWK program.  For each pattern that the record matches, the  associated  action  is
       executed.  The patterns are tested in the order they occur in the program.

       Finally,  after  all  the  input  is  exhausted,  gawk executes the code in the END
       block(s) (if any).

VARIABLES, RECORDS AND FIELDS
       AWK variables are dynamic; they come into  existence  when  they  are  first  used.
       Their  values are either floating-point numbers or strings, or both, depending upon
       how they are used.  AWK also has  one  dimensional  arrays;  arrays  with  multiple
       dimensions  may  be  simulated.  Several pre-defined variables are set as a program
       runs; these are described as needed and summarized below.

   Records
       Normally, records are separated by newline characters.  You can control how records
       are separated by assigning values to the built-in variable RS.  If RS is any single
       character, that character separates records.  Otherwise, RS is  a  regular  expres-
       sion.  Text in the input that matches this regular expression separates the record.
       However, in compatibility mode, only the first character of  its  string  value  is
       used  for  separating  records.   If RS is set to the null string, then records are
       separated by blank lines.  When RS is set to the null string, the newline character
       always acts as a field separator, in addition to whatever value FS may have.

   Fields
       As  each  input record is read, gawk splits the record into fields, using the value
       of the FS variable as the field separator.  If FS is a single character, fields are
       separated  by that character.  If FS is the null string, then each individual char-
       acter becomes a separate field.  Otherwise, FS is expected to  be  a  full  regular
       expression.  In the special case that FS is a single space, fields are separated by
       runs of spaces and/or tabs and/or newlines.  (But see the section POSIX COMPATIBIL-
       ITY, below).  NOTE: The value of IGNORECASE (see below) also affects how fields are
       split when FS is a regular expression, and how records are separated when RS  is  a
       regular expression.

       If the FIELDWIDTHS variable is set to a space separated list of numbers, each field
       is expected to have fixed width, and gawk splits up the record using the  specified
       widths.  The value of FS is ignored.  Assigning a new value to FS overrides the use
       of FIELDWIDTHS, and restores the default behavior.

       Each field in the input record may be referenced by its position, $1,  $2,  and  so
       on.  $0 is the whole record.  Fields need not be referenced by constants:

              n = 5
              print $n

       prints the fifth field in the input record.

       The variable NF is set to the total number of fields in the input record.

       References  to non-existent fields (i.e. fields after $NF) produce the null-string.
       However, assigning to a non-existent field (e.g., $(NF+2) = 5) increases the  value
       of  NF,  creates  any  intervening  fields with the null string as their value, and
       causes the value of $0 to be recomputed, with the fields  being  separated  by  the
       value  of OFS.  References to negative numbered fields cause a fatal error.  Decre-
       menting NF causes the values of fields past the new value to be lost, and the value
       of $0 to be recomputed, with the fields being separated by the value of OFS.

       Assigning  a  value to an existing field causes the whole record to be rebuilt when
       $0 is referenced.  Similarly, assigning a value to  $0  causes  the  record  to  be
       resplit, creating new values for the fields.

   Built-in Variables
       Gawk's built-in variables are:


       ARGC        The number of command line arguments (does not include options to gawk,
                   or the program source).

       ARGIND      The index in ARGV of the current file being processed.

       ARGV        Array of command line arguments.  The array is indexed from 0 to ARGC -
                   1.   Dynamically  changing  the  contents of ARGV can control the files
                   used for data.

       BINMODE     On non-POSIX systems, specifies use of "binary" mode for all file  I/O.
                   Numeric  values  of 1, 2, or 3, specify that input files, output files,
                   or all files, respectively, should use binary I/O.   String  values  of
                   "r",  or  "w"  specify that input files, or output files, respectively,
                   should use binary I/O.  String values of "rw" or "wr" specify that  all
                   files  should  use  binary  I/O.   Any other string value is treated as
                   "rw", but generates a warning message.

       CONVFMT     The conversion format for numbers, "%.6g", by default.

       ENVIRON     An array containing the values of the current environment.   The  array
                   is  indexed  by the environment variables, each element being the value
                   of that variable (e.g., ENVIRON["HOME"] might be /home/arnold).  Chang-
                   ing  this  array does not affect the environment seen by programs which
                   gawk spawns via redirection or the system() function.

       ERRNO       If a system error occurs either doing a redirection for getline, during
                   a  read  for  getline,  or  during a close(), then ERRNO will contain a
                   string describing the error.  The value is subject  to  translation  in
                   non-English locales.

       FIELDWIDTHS A white-space separated list of fieldwidths.  When set, gawk parses the
                   input into fields of fixed width, instead of using the value of the  FS
                   variable as the field separator.

       FILENAME    The  name  of the current input file.  If no files are specified on the
                   command line, the value of FILENAME is "-".  However, FILENAME is unde-
                   fined inside the BEGIN block (unless set by getline).

       FNR         The input record number in the current input file.

       FS          The input field separator, a space by default.  See Fields, above.

       IGNORECASE  Controls  the  case-sensitivity  of  all  regular expression and string
                   operations.  If IGNORECASE has a non-zero value,  then  string  compar-
                   isons  and  pattern  matching in rules, field splitting with FS, record
                   separating with RS, regular expression matching with ~ and !~, and  the
                   gensub(),  gsub(),  index(), match(), split(), and sub() built-in func-
                   tions all ignore case when doing regular expression operations.   NOTE:
                   Array  subscripting is not affected.  However, the asort() and asorti()
                   functions are affected.
                   Thus, if IGNORECASE is not equal to  zero,  /aB/  matches  all  of  the
                   strings  "ab",  "aB",  "Ab",  and "AB".  As with all AWK variables, the
                   initial value of IGNORECASE is zero,  so  all  regular  expression  and
                   string  operations  are  normally case-sensitive.  Under Unix, the full
                   ISO 8859-1 Latin-1 character set is used when  ignoring  case.   As  of
                   gawk 3.1.4, the case equivalencies are fully locale-aware, based on the
                   C <ctype.h> facilities such as isalpha(), and toupper().

       LINT        Provides dynamic control of the --lint option from within an  AWK  pro-
                   gram.   When  true, gawk prints lint warnings. When false, it does not.
                   When assigned the string value  "fatal",  lint  warnings  become  fatal
                   errors,  exactly  like  --lint=fatal.  Any other true value just prints
                   warnings.

       NF          The number of fields in the current input record.

       NR          The total number of input records seen so far.

       OFMT        The output format for numbers, "%.6g", by default.

       OFS         The output field separator, a space by default.

       ORS         The output record separator, by default a newline.

       PROCINFO    The elements of this array provide access to information about the run-
                   ning AWK program.  On some systems, there may be elements in the array,
                   "group1" through "groupn" for some n, which is the number of supplemen-
                   tary  groups  that  the  process  has.  Use the in operator to test for
                   these elements.  The following elements are guaranteed to be available:

                   PROCINFO["egid"]   the value of the getegid(2) system call.

                   PROCINFO["euid"]   the value of the geteuid(2) system call.

                   PROCINFO["FS"]     "FS"  if  field  splitting  with FS is in effect, or
                                      "FIELDWIDTHS" if field splitting with FIELDWIDTHS is
                                      in effect.

                   PROCINFO["gid"]    the value of the getgid(2) system call.

                   PROCINFO["pgrpid"] the process group ID of the current process.

                   PROCINFO["pid"]    the process ID of the current process.

                   PROCINFO["ppid"]   the parent process ID of the current process.

                   PROCINFO["uid"]    the value of the getuid(2) system call.

                   PROCINFO["version"]
                                      The version of gawk.  This is available from version
                                      3.1.4 and later.

       RS          The input record separator, by default a newline.

       RT          The record terminator.  Gawk sets RT to the input text that matched the
                   character or regular expression specified by RS.

       RSTART      The  index  of  the  first character matched by match(); 0 if no match.
                   (This implies that character indices start at one.)

       RLENGTH     The length of the string matched by match(); -1 if no match.

       SUBSEP      The character used to separate multiple subscripts in  array  elements,
                   by default "\034".

       TEXTDOMAIN  The text domain of the AWK program; used to find the localized transla-
                   tions for the program's strings.

   Arrays
       Arrays are subscripted with an expression between square brackets ([  and  ]).   If
       the  expression is an expression list (expr, expr ...)  then the array subscript is
       a string consisting of the concatenation of the (string) value of each  expression,
       separated  by  the value of the SUBSEP variable.  This facility is used to simulate
       multiply dimensioned arrays.  For example:

              i = "A"; j = "B"; k = "C"
              x[i, j, k] = "hello, world\n"

       assigns the string "hello, world\n" to the element of the array x which is  indexed
       by  the  string  "A\034B\034C".  All arrays in AWK are associative, i.e. indexed by
       string values.

       The special operator in may be used to test if an array has an index consisting  of
       a particular value.

              if (val in array)
                   print array[val]

       If the array has multiple subscripts, use (i, j) in array.

       The in construct may also be used in a for loop to iterate over all the elements of
       an array.

       An element may be deleted from an array using the  delete  statement.   The  delete
       statement may also be used to delete the entire contents of an array, just by spec-
       ifying the array name without a subscript.

   Variable Typing And Conversion
       Variables and fields may be (floating point) numbers, or strings, or both.  How the
       value  of a variable is interpreted depends upon its context.  If used in a numeric
       expression, it will be treated as a number; if used as a string it will be  treated
       as a string.

       To  force  a  variable  to  be  treated as a number, add 0 to it; to force it to be
       treated as a string, concatenate it with the null string.

       When a string must be converted to a number, the conversion is  accomplished  using
       strtod(3).   A  number  is converted to a string by using the value of CONVFMT as a
       format string for sprintf(3), with the numeric value of the variable as  the  argu-
       ment.   However, even though all numbers in AWK are floating-point, integral values
       are always converted as integers.  Thus, given

              CONVFMT = "%2.2f"
              a = 12
              b = a ""

       the variable b has a string value of "12" and not "12.00".

       When operating in POSIX mode (such as with the --posix command line option), beware
       that  locale  settings  may interfere with the way decimal numbers are treated: the
       decimal separator of the numbers you are feeding to gawk must conform to what  your
       locale would expect, be it a comma (,) or a period (.).

       Gawk  performs  comparisons as follows: If two variables are numeric, they are com-
       pared numerically.  If one value is numeric and the other has a string  value  that
       is  a "numeric string," then comparisons are also done numerically.  Otherwise, the
       numeric value is converted to a string and a string comparison is  performed.   Two
       strings are compared, of course, as strings.

       Note  that string constants, such as "57", are not numeric strings, they are string
       constants.  The idea of "numeric string" only applies  to  fields,  getline  input,
       FILENAME,  ARGV  elements, ENVIRON elements and the elements of an array created by
       split() that are numeric strings.  The basic idea is that user input, and only user
       input, that looks numeric, should be treated that way.

       Uninitialized variables have the numeric value 0 and the string value "" (the null,
       or empty, string).

   Octal and Hexadecimal Constants
       Starting with version 3.1 of gawk , you may use C-style octal and hexadecimal  con-
       stants  in your AWK program source code.  For example, the octal value 011 is equal
       to decimal 9, and the hexadecimal value 0x11 is equal to decimal 17.

   String Constants
       String constants in AWK are sequences of characters enclosed between double  quotes
       (").  Within strings, certain escape sequences are recognized, as in C.  These are:


       \\   A literal backslash.

       \a   The "alert" character; usually the ASCII BEL character.

       \b   backspace.

       \f   form-feed.

       \n   newline.

       \r   carriage return.

       \t   horizontal tab.

       \v   vertical tab.

       \xhex digits
            The character represented by the string of hexadecimal  digits  following  the
            \x.  As in ANSI C, all following hexadecimal digits are considered part of the
            escape sequence.  (This feature should tell us something about language design
            by committee.)  E.g., "\x1B" is the ASCII ESC (escape) character.

       \ddd The  character represented by the 1-, 2-, or 3-digit sequence of octal digits.
            E.g., "\033" is the ASCII ESC (escape) character.

       \c   The literal character c.

       The escape sequences may also be used inside constant  regular  expressions  (e.g.,
       /[ \t\f\n\r\v]/ matches whitespace characters).

       In  compatibility  mode, the characters represented by octal and hexadecimal escape
       sequences are treated literally when used in regular expression  constants.   Thus,
       /a\52b/ is equivalent to /a\*b/.

PATTERNS AND ACTIONS
       AWK  is  a  line-oriented  language.  The pattern comes first, and then the action.
       Action statements are enclosed in { and }.  Either the pattern may be  missing,  or
       the  action  may  be missing, but, of course, not both.  If the pattern is missing,
       the action is executed for every single record  of  input.   A  missing  action  is
       equivalent to

              { print }

       which prints the entire record.

       Comments  begin  with  the  "#"  character, and continue until the end of the line.
       Blank lines may be used to separate statements.  Normally, a statement ends with  a
       newline,  however,  this is not the case for lines ending in a ",", {, ?, :, &&, or
       ||.  Lines ending in do or else also have their statements automatically  continued
       on the following line.  In other cases, a line can be continued by ending it with a
       "\", in which case the newline will be ignored.

       Multiple statements may be put on one line by separating them  with  a  ";".   This
       applies to both the statements within the action part of a pattern-action pair (the
       usual case), and to the pattern-action statements themselves.

   Patterns
       AWK patterns may be one of the following:

              BEGIN
              END
              /regular expression/
              relational expression
              pattern && pattern
              pattern || pattern
              pattern ? pattern : pattern
              (pattern)
              ! pattern
              pattern1, pattern2

       BEGIN and END are two special kinds of patterns which are not  tested  against  the
       input.   The action parts of all BEGIN patterns are merged as if all the statements
       had been written in a single BEGIN block.  They are  executed  before  any  of  the
       input is read.  Similarly, all the END blocks are merged, and executed when all the
       input is exhausted (or when an exit statement is executed).  BEGIN and END patterns
       cannot  be combined with other patterns in pattern expressions.  BEGIN and END pat-
       terns cannot have missing action parts.

       For /regular expression/ patterns, the associated statement is  executed  for  each
       input record that matches the regular expression.  Regular expressions are the same
       as those in egrep(1), and are summarized below.

       A relational expression may use any of the operators defined below in  the  section
       on  actions.   These  generally  test  whether certain fields match certain regular
       expressions.

       The &&, ||, and !  operators are logical AND, logical OR, and logical NOT,  respec-
       tively,  as in C.  They do short-circuit evaluation, also as in C, and are used for
       combining more primitive pattern expressions.  As in  most  languages,  parentheses
       may be used to change the order of evaluation.

       The  ?: operator is like the same operator in C.  If the first pattern is true then
       the pattern used for testing is the second pattern,  otherwise  it  is  the  third.
       Only one of the second and third patterns is evaluated.

       The pattern1, pattern2 form of an expression is called a range pattern.  It matches
       all input records starting with a record  that  matches  pattern1,  and  continuing
       until  a  record  that  matches  pattern2, inclusive.  It does not combine with any
       other sort of pattern expression.

   Regular Expressions
       Regular expressions are the extended kind found in egrep.   They  are  composed  of
       characters as follows:

       c          matches the non-metacharacter c.

       \c         matches the literal character c.

       .          matches any character including newline.

       ^          matches the beginning of a string.

       $          matches the end of a string.

       [abc...]   character list, matches any of the characters abc....

       [^abc...]  negated character list, matches any character except abc....

       r1|r2      alternation: matches either r1 or r2.

       r1r2       concatenation: matches r1, and then r2.

       r+         matches one or more r's.

       r*         matches zero or more r's.

       r?         matches zero or one r's.

       (r)        grouping: matches r.

       r{n}
       r{n,}
       r{n,m}     One  or  two  numbers  inside  braces denote an interval expression.  If
                  there is one number in the braces, the preceding regular expression r is
                  repeated  n  times.  If there are two numbers separated by a comma, r is
                  repeated n to m times.  If there is one number followed by a comma, then
                  r is repeated at least n times.
                  Interval expressions are only available if either --posix or --re-inter-
                  val is specified on the command line.

       \y         matches the empty string at either the beginning or the end of a word.

       \B         matches the empty string within a word.

       \<         matches the empty string at the beginning of a word.

       \>         matches the empty string at the end of a word.

       \w         matches any word-constituent character (letter, digit, or underscore).

       \W         matches any character that is not word-constituent.

       \'         matches the empty string at the beginning of a buffer (string).

       \'         matches the empty string at the end of a buffer.

       The escape sequences that are valid in string constants (see below) are also  valid
       in regular expressions.

       Character  classes  are  a  feature  introduced in the POSIX standard.  A character
       class is a special notation for describing lists of characters that have a specific
       attribute,  but  where  the  actual  characters themselves can vary from country to
       country and/or from character set to character set.  For  example,  the  notion  of
       what is an alphabetic character differs in the USA and in France.

       A  character  class  is only valid in a regular expression inside the brackets of a
       character list.  Character classes consist of [:, a keyword denoting the class, and
       :].  The character classes defined by the POSIX standard are:

       [:alnum:]  Alphanumeric characters.

       [:alpha:]  Alphabetic characters.

       [:blank:]  Space or tab characters.

       [:cntrl:]  Control characters.

       [:digit:]  Numeric characters.

       [:graph:]  Characters  that are both printable and visible.  (A space is printable,
                  but not visible, while an a is both.)

       [:lower:]  Lower-case alphabetic characters.

       [:print:]  Printable characters (characters that are not control characters.)

       [:punct:]  Punctuation characters (characters that are not letter, digits,  control
                  characters, or space characters).

       [:space:]  Space characters (such as space, tab, and formfeed, to name a few).

       [:upper:]  Upper-case alphabetic characters.

       [:xdigit:] Characters that are hexadecimal digits.

       For example, before the POSIX standard, to match alphanumeric characters, you would
       have had to write /[A-Za-z0-9]/.  If your character set had other alphabetic  char-
       acters in it, this would not match them, and if your character set collated differ-
       ently from ASCII, this might not even  match  the  ASCII  alphanumeric  characters.
       With the POSIX character classes, you can write /[[:alnum:]]/, and this matches the
       alphabetic and numeric characters in your character set, no matter what it is.

       Two additional special sequences can appear in character  lists.   These  apply  to
       non-ASCII character sets, which can have single symbols (called collating elements)
       that are represented with more than one character, as well  as  several  characters
       that are equivalent for collating, or sorting, purposes.  (E.g., in French, a plain
       "e" and a grave-accented "`" are equivalent.)

       Collating Symbols
              A collating symbol is a multi-character collating  element  enclosed  in  [.
              and  .].   For  example,  if  ch is a collating element, then [[.ch.]]  is a
              regular expression that matches this collating element, while [ch] is a reg-
              ular expression that matches either c or h.

       Equivalence Classes
              An equivalence class is a locale-specific name for a list of characters that
              are equivalent.  The name is enclosed in [= and =].  For example, the name e
              might  be used to represent all of "e," "?," and "`."  In this case, [[=e=]]
              is a regular expression that matches any of e, ?, or `.

       These features are very valuable in  non-English  speaking  locales.   The  library
       functions  that  gawk uses for regular expression matching currently only recognize
       POSIX character classes; they do not recognize  collating  symbols  or  equivalence
       classes.

       The  \y,  \B,  \<,  \>, \w, \W, \', and \' operators are specific to gawk; they are
       extensions based on facilities in the GNU regular expression libraries.

       The various command line options control how gawk interprets characters in  regular
       expressions.

       No options
              In  the  default  case,  gawk  provide  all  the facilities of POSIX regular
              expressions and the GNU regular expression operators described above.   How-
              ever, interval expressions are not supported.

       --posix
              Only POSIX regular expressions are supported, the GNU operators are not spe-
              cial.  (E.g., \w matches a literal w).  Interval  expressions  are  allowed.
              PLEASE  NOTE that the regular expression [A-Z] will also match the lowercase
              characters in this case! Consult the info pages of  gawk  utility  for  more
              information about this behaviour.

       --traditional
              Traditional Unix awk regular expressions are matched.  The GNU operators are
              not special, interval expressions are not available,  and  neither  are  the
              POSIX  character  classes  ([[:alnum:]] and so on).  Characters described by
              octal and hexadecimal escape sequences are treated literally, even  if  they
              represent regular expression metacharacters.

       --re-interval
              Allow interval expressions in regular expressions, even if --traditional has
              been provided.

   Actions
       Action statements are enclosed in braces, { and }.  Action  statements  consist  of
       the  usual assignment, conditional, and looping statements found in most languages.
       The operators, control statements, and input/output statements available  are  pat-
       terned after those in C.

   Operators
       The operators in AWK, in order of decreasing precedence, are


       (...)       Grouping

       $           Field reference.

       ++ --       Increment and decrement, both prefix and postfix.

       ^           Exponentiation  (** may also be used, and **= for the assignment opera-
                   tor).

       + - !       Unary plus, unary minus, and logical negation.

       * / %       Multiplication, division, and modulus.

       + -         Addition and subtraction.

       space       String concatenation.

       | |&        Piped I/O for getline, print, and printf.

       < >
       <= >=
       != ==       The regular relational operators.

       ~ !~        Regular expression match, negated match.  NOTE: Do not use  a  constant
                   regular  expression  (/foo/)  on the left-hand side of a ~ or !~.  Only
                   use one on the right-hand side.  The expression /foo/  ~  exp  has  the
                   same  meaning  as  (($0  ~ /foo/) ~ exp).  This is usually not what was
                   intended.

       in          Array membership.

       &&          Logical AND.

       ||          Logical OR.

       ?:          The C conditional expression.  This has the form expr1 ? expr2 : expr3.
                   If expr1 is true, the value of the expression is expr2, otherwise it is
                   expr3.  Only one of expr2 and expr3 is evaluated.

       = += -=
       *= /= %= ^= Assignment.  Both absolute  assignment  (var  =  value)  and  operator-
                   assignment (the other forms) are supported.

   Control Statements
       The control statements are as follows:

              if (condition) statement [ else statement ]
              while (condition) statement
              do statement while (condition)
              for (expr1; expr2; expr3) statement
              for (var in array) statement
              break
              continue
              delete array[index]
              delete array
              exit [ expression ]
              { statements }

   I/O Statements
       The input/output statements are as follows:


       close(file [, how])   Close file, pipe or co-process.  The optional how should only
                             be used when closing one end of a two-way pipe to  a  co-pro-
                             cess.  It must be a string value, either "to" or "from".

       getline               Set $0 from next input record; set NF, NR, FNR.

       getline <file         Set $0 from next record of file; set NF.

       getline var           Set var from next input record; set NR, FNR.

       getline var <file     Set var from next record of file.

       command | getline [var]
                             Run  command  piping  the  output  either  into $0 or var, as
                             above.

       command |& getline [var]
                             Run command as a co-process piping the output either into  $0
                             or  var, as above.  Co-processes are a gawk extension.  (com-
                             mand can also be a socket.  See the subsection  Special  File
                             Names, below.)

       next                  Stop  processing  the  current  input record.  The next input
                             record is read and processing starts over with the first pat-
                             tern  in  the  AWK  program.  If the end of the input data is
                             reached, the END block(s), if any, are executed.

       nextfile              Stop processing the  current  input  file.   The  next  input
                             record  read  comes  from  the next input file.  FILENAME and
                             ARGIND are updated, FNR is reset to 1, and processing  starts
                             over with the first pattern in the AWK program. If the end of
                             the input data is reached, the END block(s), if any, are exe-
                             cuted.

       print                 Prints  the  current record.  The output record is terminated
                             with the value of the ORS variable.

       print expr-list       Prints expressions.  Each  expression  is  separated  by  the
                             value  of  the OFS variable.  The output record is terminated
                             with the value of the ORS variable.

       print expr-list >file Prints expressions on file.  Each expression is separated  by
                             the  value  of the OFS variable.  The output record is termi-
                             nated with the value of the ORS variable.

       printf fmt, expr-list Format and print.

       printf fmt, expr-list >file
                             Format and print on file.

       system(cmd-line)      Execute the command cmd-line, and  return  the  exit  status.
                             (This may not be available on non-POSIX systems.)

       fflush([file])        Flush  any  buffers  associated  with the open output file or
                             pipe file.  If file  is  missing,  then  standard  output  is
                             flushed.   If  file  is the null string, then all open output
                             files and pipes have their buffers flushed.

       Additional output redirections are allowed for print and printf.

       print ... >> file
              Appends output to the file.

       print ... | command
              Writes on a pipe.

       print ... |& command
              Sends data to a co-process or socket.  (See also the subsection Special File
              Names, below.)

       The  getline  command  returns  1 on success, 0 on end of file, and -1 on an error.
       Upon an error, ERRNO contains a string describing the problem.

       NOTE: If using a pipe, co-process, or socket to getline, or from  print  or  printf
       within  a  loop,  you  must  use  close() to create new instances of the command or
       socket.  AWK does not automatically close pipes, sockets, or co-processes when they
       return EOF.

   The printf Statement
       The  AWK versions of the printf statement and sprintf() function (see below) accept
       the following conversion specification formats:

       %c      An ASCII character.  If the argument used for %c is numeric, it is  treated
               as  a  character  and  printed.  Otherwise, the argument is assumed to be a
               string, and the only first character of that string is printed.

       %d, %i  A decimal number (the integer part).

       %e, %E  A floating point number of the form [-]d.dddddde[+-]dd.  The %E format uses
               E instead of e.

       %f, %F  A  floating  point number of the form [-]ddd.dddddd.  If the system library
               supports it, %F is available as well. This is like  %f,  but  uses  capital
               letters  for  special  "not  a  number" and "infinity" values. If %F is not
               available, gawk uses %f.

       %g, %G  Use %e or %f conversion, whichever is shorter,  with  nonsignificant  zeros
               suppressed.  The %G format uses %E instead of %e.

       %o      An unsigned octal number (also an integer).

       %u      An unsigned decimal number (again, an integer).

       %s      A character string.

       %x, %X  An  unsigned  hexadecimal  number  (an integer).  The %X format uses ABCDEF
               instead of abcdef.

       %%      A single % character; no argument is converted.

       NOTE: When using the integer format-control letters for values that are outside the
       range  of a C long integer, gawk switches to the %0f format specifier. If --lint is
       provided on the command line gawk warns about this.   Other  versions  of  awk  may
       print invalid values or do something else entirely.

       Optional, additional parameters may lie between the % and the control letter:

       count$ Use the count'th argument at this point in the formatting.  This is called a
              positional specifier and is intended primarily for use  in  translated  ver-
              sions  of format strings, not in the original text of an AWK program.  It is
              a gawk extension.

       -      The expression should be left-justified within its field.

       space  For numeric conversions, prefix positive values with a space,  and  negative
              values with a minus sign.

       +      The  plus  sign,  used before the width modifier (see below), says to always
              supply a sign for numeric conversions, even if the data to be  formatted  is
              positive.  The + overrides the space modifier.

       #      Use an "alternate form" for certain control letters.  For %o, supply a lead-
              ing zero.  For %x, and %X, supply a leading 0x or 0X for a  nonzero  result.
              For  %e, %E, %f and %F, the result always contains a decimal point.  For %g,
              and %G, trailing zeros are not removed from the result.

       0      A leading 0 (zero) acts as a flag, that indicates output  should  be  padded
              with zeroes instead of spaces.  This applies even to non-numeric output for-
              mats.  This flag only has an effect when the field width is wider  than  the
              value to be printed.

       width  The field should be padded to this width.  The field is normally padded with
              spaces.  If the 0 flag has been used, it is padded with zeroes.

       .prec  A number that specifies the precision to use when printing.  For the %e, %E,
              %f  and %F, formats, this specifies the number of digits you want printed to
              the right of the decimal point.  For the %g, and %G  formats,  it  specifies
              the  maximum  number of significant digits.  For the %d, %o, %i, %u, %x, and
              %X formats, it specifies the minimum number of digits to print.  For %s,  it
              specifies  the  maximum  number of characters from the string that should be
              printed.

       The dynamic width and prec capabilities of the ANSI C printf()  routines  are  sup-
       ported.   A * in place of either the width or prec specifications causes their val-
       ues to be taken from the argument list to printf or sprintf().  To use a positional
       specifier  with  a dynamic width or precision, supply the count$ after the * in the
       format string.  For example, "%3$*2$.*1$s".

   Special File Names
       When doing I/O redirection from either print or printf into a file, or via  getline
       from a file, gawk recognizes certain special filenames internally.  These filenames
       allow access to open file descriptors inherited from gawk's parent process (usually
       the  shell).   These  file  names may also be used on the command line to name data
       files.  The filenames are:

       /dev/stdin  The standard input.

       /dev/stdout The standard output.

       /dev/stderr The standard error output.

       /dev/fd/n   The file associated with the open file descriptor n.

       These are particularly useful for error messages.  For example:

              print "You blew it!" > "/dev/stderr"

       whereas you would otherwise have to use

              print "You blew it!" | "cat 1>&2"

       The following special filenames may be used with the  |&  co-process  operator  for
       creating TCP/IP network connections.

       /inet/tcp/lport/rhost/rport  File  for  TCP/IP  connection  on  local port lport to
                                    remote host rhost on remote port rport.  Use a port of
                                    0 to have the system pick a port.

       /inet/udp/lport/rhost/rport  Similar, but use UDP/IP instead of TCP/IP.

       /inet/raw/lport/rhost/rport  Reserved for future use.

       Other  special  filenames provide access to information about the running gawk pro-
       cess.  These filenames are now obsolete.  Use the  PROCINFO  array  to  obtain  the
       information they provide.  The filenames are:

       /dev/pid    Reading  this  file  returns  the process ID of the current process, in
                   decimal, terminated with a newline.

       /dev/ppid   Reading this file returns the parent process ID of the current process,
                   in decimal, terminated with a newline.

       /dev/pgrpid Reading  this file returns the process group ID of the current process,
                   in decimal, terminated with a newline.

       /dev/user   Reading this file returns a single record terminated  with  a  newline.
                   The fields are separated with spaces.  $1 is the value of the getuid(2)
                   system call, $2 is the value of the geteuid(2) system call, $3  is  the
                   value  of  the  getgid(2) system call, and $4 is the value of the gete-
                   gid(2) system call.  If there are any additional fields, they  are  the
                   group  IDs  returned  by getgroups(2).  Multiple groups may not be sup-
                   ported on all systems.

   Numeric Functions
       AWK has the following built-in arithmetic functions:


       atan2(y, x)   Returns the arctangent of y/x in radians.

       cos(expr)     Returns the cosine of expr, which is in radians.

       exp(expr)     The exponential function.

       int(expr)     Truncates to integer.

       log(expr)     The natural logarithm function.

       rand()        Returns a random number N, between 0 and 1, such that 0 <= N < 1.

       sin(expr)     Returns the sine of expr, which is in radians.

       sqrt(expr)    The square root function.

       srand([expr]) Uses expr as a new seed for the random number generator.  If no  expr
                     is provided, the time of day is used.  The return value is the previ-
                     ous seed for the random number generator.

   String Functions
       Gawk has the following built-in string functions:


       asort(s [, d])          Returns the number of elements in the source array s.   The
                               contents of s are sorted using gawk's normal rules for com-
                               paring values, and the indices of the sorted  values  of  s
                               are  replaced  with sequential integers starting with 1. If
                               the optional destination array d is specified,  then  s  is
                               first  duplicated into d, and then d is sorted, leaving the
                               indices of the source array s unchanged.

       asorti(s [, d])         Returns the number of elements in the source array s.   The
                               behavior  is  the  same as that of asort(), except that the
                               array indices are used for sorting, not the  array  values.
                               When done, the array is indexed numerically, and the values
                               are those of the original indices.  The original values are
                               lost;  thus  provide a second array if you wish to preserve
                               the original.

       gensub(r, s, h [, t])   Search the target string  t  for  matches  of  the  regular
                               expression r.  If h is a string beginning with g or G, then
                               replace all matches of r with s.  Otherwise, h is a  number
                               indicating  which  match of r to replace.  If t is not sup-
                               plied, $0 is used instead.  Within the replacement text  s,
                               the  sequence  \n,  where  n is a digit from 1 to 9, may be
                               used to indicate just the text that matched the n'th paren-
                               thesized  subexpression.   The  sequence  \0 represents the
                               entire matched text, as does the character &.  Unlike sub()
                               and  gsub(),  the modified string is returned as the result
                               of the function, and the  original  target  string  is  not
                               changed.

       gsub(r, s [, t])        For each substring matching the regular expression r in the
                               string t, substitute the string s, and return the number of
                               substitutions.   If t is not supplied, use $0.  An & in the
                               replacement text is replaced with the text that  was  actu-
                               ally  matched.   Use  \& to get a literal &.  (This must be
                               typed as "\\&"; see GAWK: Effective AWK Programming  for  a
                               fuller  discussion  of the rules for &'s and backslashes in
                               the replacement text of sub(), gsub(), and gensub().)

       index(s, t)             Returns the index of the string t in the string s, or 0  if
                               t  is  not  present.   (This implies that character indices
                               start at one.)

       length([s])             Returns the length of the string s, or the length of $0  if
                               s  is not supplied.  Starting with version 3.1.5, as a non-
                               standard  extension,  with  an  array  argument,   length()
                               returns the number of elements in the array.

       match(s, r [, a])       Returns  the  position  in s where the regular expression r
                               occurs, or 0 if r is not present, and sets  the  values  of
                               RSTART  and  RLENGTH.   Note that the argument order is the
                               same as for the ~ operator: str ~ re.  If array a  is  pro-
                               vided,  a  is  cleared  and  then  elements 1 through n are
                               filled with the portions of s that match the  corresponding
                               parenthesized  subexpression  in  r.  The 0'th element of a
                               contains the portion of s matched  by  the  entire  regular
                               expression r.  Subscripts a[n, "start"], and a[n, "length"]
                               provide the starting index in the string and length respec-
                               tively, of each matching substring.

       split(s, a [, r])       Splits the string s into the array a on the regular expres-
                               sion r, and returns the number of fields.  If r is omitted,
                               FS  is used instead.  The array a is cleared first.  Split-
                               ting behaves  identically  to  field  splitting,  described
                               above.

       sprintf(fmt, expr-list) Prints  expr-list according to fmt, and returns the result-
                               ing string.

       strtonum(str)           Examines str, and returns its numeric value.  If str begins
                               with  a  leading 0, strtonum() assumes that str is an octal
                               number.  If str begins with a leading 0x or 0X,  strtonum()
                               assumes that str is a hexadecimal number.

       sub(r, s [, t])         Just  like gsub(), but only the first matching substring is
                               replaced.

       substr(s, i [, n])      Returns the at most n-character substring of s starting  at
                               i.  If n is omitted, the rest of s is used.

       tolower(str)            Returns  a  copy of the string str, with all the upper-case
                               characters in str translated to their corresponding  lower-
                               case  counterparts.   Non-alphabetic  characters  are  left
                               unchanged.

       toupper(str)            Returns a copy of the string str, with all  the  lower-case
                               characters  in str translated to their corresponding upper-
                               case  counterparts.   Non-alphabetic  characters  are  left
                               unchanged.

       As  of  version 3.1.5, gawk is multibyte aware.  This means that index(), length(),
       substr() and match() all work in terms of characters, not bytes.

   Time Functions
       Since one of the primary uses of AWK programs is processing log files that  contain
       time  stamp  information,  gawk provides the following functions for obtaining time
       stamps and formatting them.


       mktime(datespec)
                 Turns datespec into a time stamp of the same form  as  returned  by  sys-
                 time().   The datespec is a string of the form YYYY MM DD HH MM SS[ DST].
                 The contents of the string are six or seven numbers representing  respec-
                 tively  the  full year including century, the month from 1 to 12, the day
                 of the month from 1 to 31, the hour of the day from 0 to 23,  the  minute
                 from  0 to 59, and the second from 0 to 60, and an optional daylight sav-
                 ing flag.  The values of these numbers need  not  be  within  the  ranges
                 specified;  for example, an hour of -1 means 1 hour before midnight.  The
                 origin-zero Gregorian calendar is assumed, with year 0 preceding  year  1
                 and  year  -1  preceding  year 0.  The time is assumed to be in the local
                 timezone.  If the daylight saving flag is positive, the time  is  assumed
                 to  be  daylight saving time; if zero, the time is assumed to be standard
                 time; and if negative  (the  default),  mktime()  attempts  to  determine
                 whether  daylight  saving  time  is in effect for the specified time.  If
                 datespec does not contain enough elements or if the resulting time is out
                 of range, mktime() returns -1.

       strftime([format [, timestamp[, utc-flag]]])
                 Formats  timestamp according to the specification in format.  If utc-flag
                 is present and is non-zero or non-null, the result is in  UTC,  otherwise
                 the result is in local time.  The timestamp should be of the same form as
                 returned by systime().  If timestamp is missing, the current time of  day
                 is used.  If format is missing, a default format equivalent to the output
                 of date(1) is used.  See the specification for the strftime() function in
                 ANSI C for the format conversions that are guaranteed to be available.

       systime() Returns  the current time of day as the number of seconds since the Epoch
                 (1970-01-01 00:00:00 UTC on POSIX systems).

   Bit Manipulations Functions
       Starting with version 3.1 of gawk, the following  bit  manipulation  functions  are
       available.  They work by converting double-precision floating point values to uint-
       max_t integers, doing the operation, and then converting the result back to  float-
       ing point.  The functions are:

       and(v1, v2)         Return the bitwise AND of the values provided by v1 and v2.

       compl(val)          Return the bitwise complement of val.

       lshift(val, count)  Return the value of val, shifted left by count bits.

       or(v1, v2)          Return the bitwise OR of the values provided by v1 and v2.

       rshift(val, count)  Return the value of val, shifted right by count bits.

       xor(v1, v2)         Return the bitwise XOR of the values provided by v1 and v2.


   Internationalization Functions
       Starting  with version 3.1 of gawk, the following functions may be used from within
       your AWK program for translating strings at run-time.  For full details, see  GAWK:
       Effective AWK Programming.

       bindtextdomain(directory [, domain])
              Specifies  the  directory  where  gawk looks for the .mo files, in case they
              will not or cannot be placed in the  ''standard''  locations  (e.g.,  during
              testing).  It returns the directory where domain is ''bound.''
              The  default  domain  is  the value of TEXTDOMAIN.  If directory is the null
              string (""), then bindtextdomain() returns the current binding for the given
              domain.

       dcgettext(string [, domain [, category]])
              Returns  the translation of string in text domain domain for locale category
              category.  The default value for domain is the current value of  TEXTDOMAIN.
              The default value for category is "LC_MESSAGES".
              If  you supply a value for category, it must be a string equal to one of the
              known locale categories described in GAWK: Effective AWK  Programming.   You
              must  also supply a text domain.  Use TEXTDOMAIN if you want to use the cur-
              rent domain.

       dcngettext(string1 , string2 , number [, domain [, category]])
              Returns the plural form used for number of the translation  of  string1  and
              string2  in  text  domain  domain for locale category category.  The default
              value for domain is the current value of TEXTDOMAIN.  The default value  for
              category is "LC_MESSAGES".
              If  you supply a value for category, it must be a string equal to one of the
              known locale categories described in GAWK: Effective AWK  Programming.   You
              must  also supply a text domain.  Use TEXTDOMAIN if you want to use the cur-
              rent domain.

USER-DEFINED FUNCTIONS
       Functions in AWK are defined as follows:

              function name(parameter list) { statements }

       Functions are executed when they are called from within expressions in either  pat-
       terns  or  actions.   Actual  parameters  supplied in the function call are used to
       instantiate the formal parameters declared in the function.  Arrays are  passed  by
       reference, other variables are passed by value.

       Since  functions  were  not  originally part of the AWK language, the provision for
       local variables is rather clumsy: They are declared  as  extra  parameters  in  the
       parameter list.  The convention is to separate local variables from real parameters
       by extra spaces in the parameter list.  For example:

              function  f(p, q,     a, b)   # a and b are local
              {
                   ...
              }

              /abc/     { ... ; f(1, 2) ; ... }

       The left parenthesis in a function call is required to immediately follow the func-
       tion  name, without any intervening white space.  This avoids a syntactic ambiguity
       with the concatenation operator.  This restriction does not apply to  the  built-in
       functions listed above.

       Functions  may  call  each other and may be recursive.  Function parameters used as
       local variables are initialized to  the  null  string  and  the  number  zero  upon
       function invocation.

       Use  return  expr to return a value from a function.  The return value is undefined
       if no value is provided, or if the function returns by "falling off" the end.

       If --lint has been provided, gawk warns about calls to undefined functions at parse
       time, instead of at run time.  Calling an undefined function at run time is a fatal
       error.

       The word func may be used in place of function.

DYNAMICALLY LOADING NEW FUNCTIONS
       Beginning with version 3.1 of gawk, you can dynamically add new built-in  functions
       to  the  running  gawk  interpreter.  The full details are beyond the scope of this
       manual page; see GAWK: Effective AWK Programming for the details.


       extension(object, function)
               Dynamically link the shared object file named by object, and  invoke  func-
               tion  in that object, to perform initialization.  These should both be pro-
               vided as strings.  Returns the value returned by function.

       This function is provided and documented in GAWK: Effective  AWK  Programming,  but
       everything  about  this feature is likely to change eventually.  We STRONGLY recom-
       mend that you do not use this feature for anything that you aren't willing to redo.

SIGNALS
       pgawk  accepts  two signals.  SIGUSR1 causes it to dump a profile and function call
       stack to the profile file, which is either awkprof.out, or whatever file was  named
       with  the --profile option.  It then continues to run.  SIGHUP causes pgawk to dump
       the profile and function call stack and then exit.

EXAMPLES
       Print and sort the login names of all users:

            BEGIN     { FS = ":" }
                 { print $1 | "sort" }

       Count lines in a file:

                 { nlines++ }
            END  { print nlines }

       Precede each line by its number in the file:

            { print FNR, $0 }

       Concatenate and line number (a variation on a theme):

            { print NR, $0 }
       Run an external command for particular lines of data:

            tail -f access_log |
            awk '/myhome.html/ { system("nmap " $1 ">> logdir/myhome.html") }'

INTERNATIONALIZATION
       String constants are sequences of characters enclosed in double  quotes.   In  non-
       English speaking environments, it is possible to mark strings in the AWK program as
       requiring translation to the native natural language. Such strings  are  marked  in
       the AWK program with a leading underscore ("_").  For example,

              gawk 'BEGIN { print "hello, world" }'

       always prints hello, world.  But,

              gawk 'BEGIN { print _"hello, world" }'

       might print bonjour, monde in France.

       There  are  several  steps involved in producing and running a localizable AWK pro-
       gram.

       1.  Add a BEGIN action to assign a value to the TEXTDOMAIN variable to set the text
           domain to a name associated with your program.

           BEGIN { TEXTDOMAIN = "myprog" }

       This  allows  gawk to find the .mo file associated with your program.  Without this
       step, gawk uses the messages text domain, which likely does  not  contain  transla-
       tions for your program.

       2.  Mark all strings that should be translated with leading underscores.

       3.  If  necessary,  use  the  dcgettext() and/or bindtextdomain() functions in your
           program, as appropriate.

       4.  Run gawk --gen-po -f myprog.awk > myprog.po to generate a  .po  file  for  your
           program.

       5.  Provide  appropriate  translations, and build and install the corresponding .mo
           files.

       The internationalization features are described in full detail in  GAWK:  Effective
       AWK Programming.

POSIX COMPATIBILITY
       A  primary  goal for gawk is compatibility with the POSIX standard, as well as with
       the latest version of UNIX awk.  To this end, gawk incorporates the following  user
       visible  features which are not described in the AWK book, but are part of the Bell
       Laboratories version of awk, and are in the POSIX standard.

       The book indicates that command line variable assignment  happens  when  awk  would
       otherwise  open the argument as a file, which is after the BEGIN block is executed.
       However, in earlier implementations, when such an assignment  appeared  before  any
       file  names,  the assignment would happen before the BEGIN block was run.  Applica-
       tions came to depend on this "feature."  When awk was changed to match its documen-
       tation, the -v option for assigning variables before program execution was added to
       accommodate applications that depended upon the old behavior.   (This  feature  was
       agreed upon by both the Bell Laboratories and the GNU developers.)

       The -W option for implementation specific features is from the POSIX standard.

       When  processing  arguments, gawk uses the special option "--" to signal the end of
       arguments.  In compatibility mode, it warns about but otherwise  ignores  undefined
       options.   In normal operation, such arguments are passed on to the AWK program for
       it to process.

       The AWK book does not define the return value of srand().  The POSIX  standard  has
       it return the seed it was using, to allow keeping track of random number sequences.
       Therefore srand() in gawk also returns its current seed.

       Other new features are: The use of multiple -f options (from MKS awk); the  ENVIRON
       array;  the  \a, and \v escape sequences (done originally in gawk and fed back into
       the Bell Laboratories version); the  tolower()  and  toupper()  built-in  functions
       (from  the  Bell Laboratories version); and the ANSI C conversion specifications in
       printf (done first in the Bell Laboratories version).

HISTORICAL FEATURES
       There are two features  of  historical  AWK  implementations  that  gawk  supports.
       First, it is possible to call the length() built-in function not only with no argu-
       ment, but even without parentheses!  Thus,

              a = length     # Holy Algol 60, Batman!

       is the same as either of

              a = length()
              a = length($0)

       This feature is marked as "deprecated" in the POSIX standard,  and  gawk  issues  a
       warning about its use if --lint is specified on the command line.

       The other feature is the use of either the continue or the break statements outside
       the body of a while, for, or do loop.  Traditional AWK implementations have treated
       such usage as equivalent to the next statement.  Gawk supports this usage if --tra-
       ditional has been specified.

GNU EXTENSIONS
       Gawk has a number of extensions to POSIX awk.  They are described in this  section.
       All  the extensions described here can be disabled by invoking gawk with the --tra-
       ditional or --posix options.

       The following features of gawk are not available in POSIX awk.

       ? No path search is performed for files named via the  -f  option.   Therefore  the
         AWKPATH environment variable is not special.

       ? The \x escape sequence.  (Disabled with --posix.)

       ? The fflush() function.  (Disabled with --posix.)

       ? The ability to continue lines after ?  and :.  (Disabled with --posix.)

       ? Octal and hexadecimal constants in AWK programs.

       ? The ARGIND, BINMODE, ERRNO, LINT, RT and TEXTDOMAIN variables are not special.

       ? The IGNORECASE variable and its side-effects are not available.

       ? The FIELDWIDTHS variable and fixed-width field splitting.

       ? The PROCINFO array is not available.

       ? The use of RS as a regular expression.

       ? The special file names available for I/O redirection are not recognized.

       ? The |& operator for creating co-processes.

       ? The ability to split out individual characters using the null string as the value
         of FS, and as the third argument to split().

       ? The optional second argument to the close() function.

       ? The optional third argument to the match() function.

       ? The ability to use positional specifiers with printf and sprintf().

       ? The ability to pass an array to length().

       ? The use of delete array to delete the entire contents of an array.

       ? The use of nextfile to abandon processing of the current input file.

       ? The and(), asort(), asorti(),  bindtextdomain(),  compl(),  dcgettext(),  dcnget-
         text(),  gensub(),  lshift(),  mktime(),  or(), rshift(), strftime(), strtonum(),
         systime() and xor() functions.

       ? Localizable strings.

       ? Adding new built-in functions dynamically with the extension() function.

       The AWK book does not define the return value  of  the  close()  function.   Gawk's
       close() returns the value from fclose(3), or pclose(3), when closing an output file
       or pipe, respectively.  It returns the process's exit status when closing an  input
       pipe.   The return value is -1 if the named file, pipe or co-process was not opened
       with a redirection.

       When gawk is invoked with the --traditional option, if the fs argument  to  the  -F
       option is "t", then FS is set to the tab character.  Note that typing gawk -F\t ...
       simply causes the shell to quote the "t," and does not pass "\t" to the -F  option.
       Since  this  is  a  rather ugly special case, it is not the default behavior.  This
       behavior also does not occur if --posix has been specified.  To really  get  a  tab
       character as the field separator, it is best to use single quotes: gawk -F'\t' ....

       If gawk is configured with the --enable-switch option  to  the  configure  command,
       then it accepts an additional control-flow statement:
              switch (expression) {
              case value|regex : statement
              ...
              [ default: statement ]
              }

       If  gawk  is  configured  with the --disable-directories-fatal option, then it will
       silently skip directories named on the command line.  Otherwise, it will do so only
       if invoked with the --traditional option.

ENVIRONMENT VARIABLES
       The  AWKPATH environment variable can be used to provide a list of directories that
       gawk searches when looking for files named via the -f and --file options.

       If POSIXLY_CORRECT exists in the environment,  then  gawk  behaves  exactly  as  if
       --posix had been specified on the command line.  If --lint has been specified, gawk
       issues a warning message to this effect.

SEE ALSO
       egrep(1), getpid(2),  getppid(2),  getpgrp(2),  getuid(2),  geteuid(2),  getgid(2),
       getegid(2), getgroups(2)

       The  AWK  Programming  Language,  Alfred V. Aho, Brian W. Kernighan, Peter J. Wein-
       berger, Addison-Wesley, 1988.  ISBN 0-201-07981-X.

       GAWK: Effective AWK Programming, Edition 3.0, published by the Free Software  Foun-
       dation,  2001.   The  current  version  of  this  document  is  available online at
       http://www.gnu.org/software/gawk/manual.

BUGS
       The -F option is not necessary given the command line variable assignment  feature;
       it remains only for backwards compatibility.

       Syntactically  invalid  single character programs tend to overflow the parse stack,
       generating a rather unhelpful message.  Such programs are surprisingly difficult to
       diagnose  in  the  completely  general  case, and the effort to do so really is not
       worth it.

AUTHORS
       The original version of UNIX awk was designed and implemented by Alfred Aho,  Peter
       Weinberger, and Brian Kernighan of Bell Laboratories.  Brian Kernighan continues to
       maintain and enhance it.

       Paul Rubin and Jay Fenlason, of the Free Software Foundation,  wrote  gawk,  to  be
       compatible  with  the  original version of awk distributed in Seventh Edition UNIX.
       John Woods contributed a number of bug fixes.  David  Trueman,  with  contributions
       from Arnold Robbins, made gawk compatible with the new version of UNIX awk.  Arnold
       Robbins is the current maintainer.

       The initial DOS port was done by Conrad Kwok and Scott Garfinkle.  Scott Deifik  is
       the  current DOS maintainer.  Pat Rankin did the port to VMS, and Michal Jaegermann
       did the port to the Atari ST.  The port to OS/2 was done by Kai  Uwe  Rommel,  with
       contributions  and  help  from Darrel Hankerson.  Andreas Buening now maintains the
       OS/2 port.  Fred Fish supplied support for the Amiga, and Martin Brown provided the
       BeOS  port.   Stephen Davies provided the original Tandem port, and Matthew Woehlke
       provided changes for Tandem's POSIX-compliant systems.  Ralf Wildenhues  now  main-
       tains that port.

       See  the  README  file in the gawk distribution for current information about main-
       tainers and which ports are currently supported.

VERSION INFORMATION
       This man page documents gawk, version 3.1.7.

BUG REPORTS
       If you find a bug in gawk, please send electronic mail to bug-gawk AT gnu.org.  Please
       include  your  operating  system  and  its revision, the version of gawk (from gawk
       --version), what C compiler you used to compile it, and a  test  program  and  data
       that are as small as possible for reproducing the problem.

       Before  sending  a  bug report, please do the following things.  First, verify that
       you have the latest version of gawk.  Many bugs (usually subtle ones) are fixed  at
       each  release,  and  if  yours  is  out  of date, the problem may already have been
       solved.  Second, please see if setting the environment variable LC_ALL to  LC_ALL=C
       causes  things  to behave as you expect. If so, it's a locale issue, and may or may
       not really be a bug.  Finally, please read this man page and the  reference  manual
       carefully  to  be  sure  that  what you think is a bug really is, instead of just a
       quirk in the language.

       Whatever you do, do NOT post a bug report in comp.lang.awk.  While the gawk  devel-
       opers  occasionally read this newsgroup, posting bug reports there is an unreliable
       way to report bugs.  Instead, please use the electronic mail addresses given above.

       If  you're  using  a GNU/Linux system or BSD-based system, you may wish to submit a
       bug report to the vendor of your distribution.  That's fine, but please send a copy
       to the official email address as well, since there's no guarantee that the bug will
       be forwarded to the gawk maintainer.

ACKNOWLEDGEMENTS
       Brian Kernighan of Bell Laboratories provided valuable  assistance  during  testing
       and debugging.  We thank him.

COPYING PERMISSIONS
       Copyright (C) 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002,
       2003, 2004, 2005, 2007, 2009 Free Software Foundation, Inc.

       Permission is granted to make and distribute verbatim copies of  this  manual  page
       provided  the  copyright  notice  and  this  permission notice are preserved on all
       copies.

       Permission is granted to copy and distribute modified versions of this manual  page
       under  the  conditions  for  verbatim  copying,  provided that the entire resulting
       derived work is distributed under the terms of a  permission  notice  identical  to
       this one.

       Permission  is granted to copy and distribute translations of this manual page into
       another language, under the above conditions for  modified  versions,  except  that
       this permission notice may be stated in a translation approved by the Foundation.



Free Software Foundation          Jul 10 2009                          GAWK(1)

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