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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 contiguous 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 con-
tains 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 mes-
sage 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, direc-
tories 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 begin-
ning with -.
-F, --fixed-strings
Interpret PATTERN as a list of fixed strings, separated by new-
lines, 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 con-
tains zero patterns, 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 equivalent 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 outputting 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 performance. 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 --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 immedi-
ately 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 characters 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 ver-
batim; 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 offsets 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 ver-
sion 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 con-
stituent character. Similarly, it must be either at the end of
the line or followed by a non-word constituent character.
Word-constituent characters are letters, digits, and the under-
score.
-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 expressions are constructed analogously to arithmetic expres-
sions, by using various operators to combine smaller expressions.
Grep understands two different versions of regular expression syntax:
"basic" and "extended." In GNU grep, there is no difference in avail-
able functionality using either syntax. In other implementations,
basic regular expressions are less powerful. The following descrip-
tion applies to extended regular expressions; differences 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 dig-
its, are regular expressions 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 char-
acters separated by a hyphen. It matches any single character that
sorts between the two characters, inclusive, using the locale's col-
lating 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 exam-
ple. 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 expressions, 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 lit-
eral - place it last.
The period . matches any single character. The symbol \w is a syn-
onym 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 sym-
bols \< and \> respectively 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 regular expression matches any string matching either subex-
pression.
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 regu-
lar 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
implementations 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 specifica-
tion. 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 vari-
ables LC_ALL, LC_foo, LANG, in that order. The first of these vari-
ables 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 --direc-
tories=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 collating 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 deter-
mines the language 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 environment 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 com-
mand 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 other-
wise. 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-gnu-utils@gnu.org. Be sure to include the
word "grep" somewhere in the "Subject:" field.
Large repetition counts in the {n,m} construct may cause grep to use
lots of memory. In addition, certain other obscure regular expres-
sions 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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