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GREP(1) GREP(1)
NAME
grep, egrep, fgrep - print lines matching a pattern
SYNOPSIS
grep [options] PATTERN [FILE...]
grep [options] [-e PATTERN | -f FILE] [FILE...]
DESCRIPTION
Grep searches the named input FILEs (or standard input if no files are named, or
the file name - is given) for lines containing a match to the given PATTERN. By
default, grep prints the matching lines.
In addition, two variant programs egrep and fgrep are available. Egrep is the same
as grep -E. Fgrep is the same as grep -F.
OPTIONS
-A NUM, --after-context=NUM
Print NUM lines of trailing context after matching lines. Places a line
containing -- between contiguous groups of matches.
-a, --text
Process a binary file as if it were text; this is equivalent to the
--binary-files=text option.
-B NUM, --before-context=NUM
Print NUM lines of leading context before matching lines. Places a line
containing -- between contiguous groups of matches.
-C NUM, --context=NUM
Print NUM lines of output context. Places a line containing -- between con-
tiguous groups of matches.
-b, --byte-offset
Print the byte offset within the input file before each line of output.
--binary-files=TYPE
If the first few bytes of a file indicate that the file contains binary
data, assume that the file is of type TYPE. By default, TYPE is binary, and
grep normally outputs either a one-line message saying that a binary file
matches, or no message if there is no match. If TYPE is without-match, grep
assumes that a binary file does not match; this is equivalent to the -I
option. If TYPE is text, grep processes a binary file as if it were text;
this is equivalent to the -a option. Warning: grep --binary-files=text
might output binary garbage, which can have nasty side effects if the output
is a terminal and if the terminal driver interprets some of it as commands.
--colour[=WHEN], --color[=WHEN]
Surround the matching string with the marker find in GREP_COLOR environment
variable. WHEN may be 'never', 'always', or 'auto'
-c, --count
Suppress normal output; instead print a count of matching lines for each
input file. With the -v, --invert-match option (see below), count non-
matching lines.
-D ACTION, --devices=ACTION
If an input file is a device, FIFO or socket, use ACTION to process it. By
default, ACTION is read, which means that devices are read just as if they
were ordinary files. If ACTION is skip, devices are silently skipped.
-d ACTION, --directories=ACTION
If an input file is a directory, use ACTION to process it. By default,
ACTION is read, which means that directories are read just as if they were
ordinary files. If ACTION is skip, directories are silently skipped. If
ACTION is recurse, grep reads all files under each directory, recursively;
this is equivalent to the -r option.
-E, --extended-regexp
Interpret PATTERN as an extended regular expression (see below).
-e PATTERN, --regexp=PATTERN
Use PATTERN as the pattern; useful to protect patterns beginning with -.
-F, --fixed-strings
Interpret PATTERN as a list of fixed strings, separated by newlines, any of
which is to be matched.
-P, --perl-regexp
Interpret PATTERN as a Perl regular expression.
-f FILE, --file=FILE
Obtain patterns from FILE, one per line. The empty file contains zero pat-
terns, and therefore matches nothing.
-G, --basic-regexp
Interpret PATTERN as a basic regular expression (see below). This is the
default.
-H, --with-filename
Print the filename for each match.
-h, --no-filename
Suppress the prefixing of filenames on output when multiple files are
searched.
--help Output a brief help message.
-I Process a binary file as if it did not contain matching data; this is equiv-
alent to the --binary-files=without-match option.
-i, --ignore-case
Ignore case distinctions in both the PATTERN and the input files.
-L, --files-without-match
Suppress normal output; instead print the name of each input file from which
no output would normally have been printed. The scanning will stop on the
first match.
-l, --files-with-matches
Suppress normal output; instead print the name of each input file from which
output would normally have been printed. The scanning will stop on the
first match.
-m NUM, --max-count=NUM
Stop reading a file after NUM matching lines. If the input is standard
input from a regular file, and NUM matching lines are output, grep ensures
that the standard input is positioned to just after the last matching line
before exiting, regardless of the presence of trailing context lines. This
enables a calling process to resume a search. When grep stops after NUM
matching lines, it outputs any trailing context lines. When the -c or
--count option is also used, grep does not output a count greater than NUM.
When the -v or --invert-match option is also used, grep stops after out-
putting NUM non-matching lines.
--mmap If possible, use the mmap(2) system call to read input, instead of the
default read(2) system call. In some situations, --mmap yields better per-
formance. However, --mmap can cause undefined behavior (including core
dumps) if an input file shrinks while grep is operating, or if an I/O error
occurs.
-n, --line-number
Prefix each line of output with the line number within its input file.
-o, --only-matching
Show only the part of a matching line that matches PATTERN.
--label=LABEL
Displays input actually coming from standard input as input coming from file
LABEL. This is especially useful for tools like zgrep, e.g. gzip -cd
foo.gz |grep -H --label=foo something
--line-buffered
Use line buffering, it can be a performance penality.
-q, --quiet, --silent
Quiet; do not write anything to standard output. Exit immediately with zero
status if any match is found, even if an error was detected. Also see the
-s or --no-messages option.
-R, -r, --recursive
Read all files under each directory, recursively; this is equivalent to the
-d recurse option.
--include=PATTERN
Recurse in directories only searching file matching PATTERN.
--exclude=PATTERN
Recurse in directories skip file matching PATTERN.
-s, --no-messages
Suppress error messages about nonexistent or unreadable files. Portability
note: unlike GNU grep, traditional grep did not conform to POSIX.2, because
traditional grep lacked a -q option and its -s option behaved like GNU
grep's -q option. Shell scripts intended to be portable to traditional grep
should avoid both -q and -s and should redirect output to /dev/null instead.
-U, --binary
Treat the file(s) as binary. By default, under MS-DOS and MS-Windows, grep
guesses the file type by looking at the contents of the first 32KB read from
the file. If grep decides the file is a text file, it strips the CR charac-
ters from the original file contents (to make regular expressions with ^ and
$ work correctly). Specifying -U overrules this guesswork, causing all
files to be read and passed to the matching mechanism verbatim; if the file
is a text file with CR/LF pairs at the end of each line, this will cause
some regular expressions to fail. This option has no effect on platforms
other than MS-DOS and MS-Windows.
-u, --unix-byte-offsets
Report Unix-style byte offsets. This switch causes grep to report byte off-
sets as if the file were Unix-style text file, i.e. with CR characters
stripped off. This will produce results identical to running grep on a Unix
machine. This option has no effect unless -b option is also used; it has no
effect on platforms other than MS-DOS and MS-Windows.
-V, --version
Print the version number of grep to standard error. This version number
should be included in all bug reports (see below).
-v, --invert-match
Invert the sense of matching, to select non-matching lines.
-w, --word-regexp
Select only those lines containing matches that form whole words. The test
is that the matching substring must either be at the beginning of the line,
or preceded by a non-word constituent character. Similarly, it must be
either at the end of the line or followed by a non-word constituent charac-
ter. Word-constituent characters are letters, digits, and the underscore.
-x, --line-regexp
Select only those matches that exactly match the whole line.
-y Obsolete synonym for -i.
-Z, --null
Output a zero byte (the ASCII NUL character) instead of the character that
normally follows a file name. For example, grep -lZ outputs a zero byte
after each file name instead of the usual newline. This option makes the
output unambiguous, even in the presence of file names containing unusual
characters like newlines. This option can be used with commands like find
-print0, perl -0, sort -z, and xargs -0 to process arbitrary file names,
even those that contain newline characters.
REGULAR EXPRESSIONS
A regular expression is a pattern that describes a set of strings. Regular expres-
sions are constructed analogously to arithmetic expressions, by using various oper-
ators to combine smaller expressions.
Grep understands two different versions of regular expression syntax: "basic" and
"extended." In GNU grep, there is no difference in available functionality using
either syntax. In other implementations, basic regular expressions are less power-
ful. The following description applies to extended regular expressions; differ-
ences for basic regular expressions are summarized afterwards.
The fundamental building blocks are the regular expressions that match a single
character. Most characters, including all letters and digits, are regular expres-
sions that match themselves. Any metacharacter with special meaning may be quoted
by preceding it with a backslash.
A bracket expression is a list of characters enclosed by [ and ]. It matches any
single character in that list; if the first character of the list is the caret ^
then it matches any character not in the list. For example, the regular expression
[0123456789] matches any single digit.
Within a bracket expression, a range expression consists of two characters sepa-
rated by a hyphen. It matches any single character that sorts between the two
characters, inclusive, using the locale's collating sequence and character set.
For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales
sort characters in dictionary order, and in these locales [a-d] is typically not
equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example. To obtain
the traditional interpretation of bracket expressions, you can use the C locale by
setting the LC_ALL environment variable to the value C.
Finally, certain named classes of characters are predefined within bracket expres-
sions, as follows. Their names are self explanatory, and they are [:alnum:],
[:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:],
[:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means [0-9A-Za-z],
except the latter form depends upon the C locale and the ASCII character encoding,
whereas the former is independent of locale and character set. (Note that the
brackets in these class names are part of the symbolic names, and must be included
in addition to the brackets delimiting the bracket list.) Most metacharacters lose
their special meaning inside lists. To include a literal ] place it first in the
list. Similarly, to include a literal ^ place it anywhere but first. Finally, to
include a literal - place it last.
The period . matches any single character. The symbol \w is a synonym for
[[:alnum:]] and \W is a synonym for [^[:alnum]].
The caret ^ and the dollar sign $ are metacharacters that respectively match the
empty string at the beginning and end of a line. The symbols \< and \> respec-
tively match the empty string at the beginning and end of a word. The symbol \b
matches the empty string at the edge of a word, and \B matches the empty string
provided it's not at the edge of a word.
A regular expression may be followed by one of several repetition operators:
? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{n,m} The preceding item is matched at least n times, but not more than m times.
Two regular expressions may be concatenated; the resulting regular expression
matches any string formed by concatenating two substrings that respectively match
the concatenated subexpressions.
Two regular expressions may be joined by the infix operator |; the resulting regu-
lar expression matches any string matching either subexpression.
Repetition takes precedence over concatenation, which in turn takes precedence over
alternation. A whole subexpression may be enclosed in parentheses to override
these precedence rules.
The backreference \n, where n is a single digit, matches the substring previously
matched by the nth parenthesized subexpression of the regular expression.
In basic regular expressions the metacharacters ?, +, {, |, (, and ) lose their
special meaning; instead use the backslashed versions \?, \+, \{, \|, \(, and \).
Traditional egrep did not support the { metacharacter, and some egrep implementa-
tions support \{ instead, so portable scripts should avoid { in egrep patterns and
should use [{] to match a literal {.
GNU egrep attempts to support traditional usage by assuming that { is not special
if it would be the start of an invalid interval specification. For example, the
shell command egrep '{1' searches for the two-character string {1 instead of
reporting a syntax error in the regular expression. POSIX.2 allows this behavior
as an extension, but portable scripts should avoid it.
ENVIRONMENT VARIABLES
Grep's behavior is affected by the following environment variables.
A locale LC_foo is specified by examining the three environment variables LC_ALL,
LC_foo, LANG, in that order. The first of these variables that is set specifies
the locale. For example, if LC_ALL is not set, but LC_MESSAGES is set to pt_BR,
then Brazilian Portuguese is used for the LC_MESSAGES locale. The C locale is used
if none of these environment variables are set, or if the locale catalog is not
installed, or if grep was not compiled with national language support (NLS).
GREP_OPTIONS
This variable specifies default options to be placed in front of any
explicit options. For example, if GREP_OPTIONS is '--binary-files=without-
match --directories=skip', grep behaves as if the two options --binary-
files=without-match and --directories=skip had been specified before any
explicit options. Option specifications are separated by whitespace. A
backslash escapes the next character, so it can be used to specify an option
containing whitespace or a backslash.
GREP_COLOR
Specifies the marker for highlighting.
LC_ALL, LC_COLLATE, LANG
These variables specify the LC_COLLATE locale, which determines the collat-
ing sequence used to interpret range expressions like [a-z].
LC_ALL, LC_CTYPE, LANG
These variables specify the LC_CTYPE locale, which determines the type of
characters, e.g., which characters are whitespace.
LC_ALL, LC_MESSAGES, LANG
These variables specify the LC_MESSAGES locale, which determines the lan-
guage that grep uses for messages. The default C locale uses American
English messages.
POSIXLY_CORRECT
If set, grep behaves as POSIX.2 requires; otherwise, grep behaves more like
other GNU programs. POSIX.2 requires that options that follow file names
must be treated as file names; by default, such options are permuted to the
front of the operand list and are treated as options. Also, POSIX.2
requires that unrecognized options be diagnosed as "illegal", but since they
are not really against the law the default is to diagnose them as "invalid".
POSIXLY_CORRECT also disables _N_GNU_nonoption_argv_flags_, described below.
_N_GNU_nonoption_argv_flags_
(Here N is grep's numeric process ID.) If the ith character of this envi-
ronment variable's value is 1, do not consider the ith operand of grep to be
an option, even if it appears to be one. A shell can put this variable in
the environment for each command it runs, specifying which operands are the
results of file name wildcard expansion and therefore should not be treated
as options. This behavior is available only with the GNU C library, and
only when POSIXLY_CORRECT is not set.
DIAGNOSTICS
Normally, exit status is 0 if selected lines are found and 1 otherwise. But the
exit status is 2 if an error occurred, unless the -q or --quiet or --silent option
is used and a selected line is found.
BUGS
Email bug reports to bug-grep AT gnu.org.
Large repetition counts in the {n,m} construct may cause grep to use lots of mem-
ory. In addition, certain other obscure regular expressions require exponential
time and space, and may cause grep to run out of memory.
Backreferences are very slow, and may require exponential time.
GNU Project 2002/01/22 GREP(1)
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