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GREP(1) General Commands Manual 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 if a single hyphen-minus (-) is given as file name) 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. Direct invocation as
either egrep or fgrep is deprecated, but is provided to allow historical
applications that rely on them to run unmodified.
OPTIONS Generic Program Information –help Print a usage message briefly summarizing these command-line options and the bug-reporting address, then exit.
-V, --version
Print the version number of grep to the standard output stream. This
version number should be included in all bug reports (see below).
Matcher Selection -E, –extended-regexp Interpret PATTERN as an extended regular expression (ERE, see below). (-E is specified by POSIX.)
-F, --fixed-strings
Interpret PATTERN as a list of fixed strings, separated by newlines,
any of which is to be matched. (-F is specified by POSIX.)
-G, --basic-regexp
Interpret PATTERN as a basic regular expression (BRE, see below).
This is the default.
-P, --perl-regexp
Interpret PATTERN as a Perl regular expression. This is highly
experimental and grep -P may warn of unimplemented features.
Matching Control -e PATTERN, –regexp=PATTERN Use PATTERN as the pattern. This can be used to specify multiple search patterns, or to protect a pattern beginning with a hyphen (-). (-e is specified by POSIX.)
-f FILE, --file=FILE
Obtain patterns from FILE, one per line. The empty file contains
zero patterns, and therefore matches nothing. (-f is specified by
POSIX.)
-i, --ignore-case
Ignore case distinctions in both the PATTERN and the input files.
(-i is specified by POSIX.)
-v, --invert-match
Invert the sense of matching, to select non-matching lines. (-v is
specified by POSIX.)
-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 character. Word-constituent
characters are letters, digits, and the underscore.
-x, --line-regexp
Select only those matches that exactly match the whole line. (-x is
specified by POSIX.)
-y Obsolete synonym for -i.
General Output Control -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. (-c is specified by POSIX.)
--color[=WHEN], --colour[=WHEN]
Surround the matched (non-empty) strings, matching lines, context
lines, file names, line numbers, byte offsets, and separators (for
fields and groups of context lines) with escape sequences to display
them in color on the terminal. The colors are defined by the
environment variable GREP_COLORS. The deprecated environment
variable GREP_COLOR is still supported, but its setting does not have
priority. WHEN is never, always, or auto.
-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. (-l is specified by POSIX.)
-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.
-o, --only-matching
Print only the matched (non-empty) parts of a matching line, with
each such part on a separate output line.
-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. (-q is specified
by POSIX.)
-s, --no-messages
Suppress error messages about nonexistent or unreadable files.
Portability note: unlike GNU grep, 7th Edition Unix grep did not
conform to POSIX, because it lacked -q and its -s option behaved like
GNU grep's -q option. USG-style grep also lacked -q but its -s
option behaved like GNU grep. Portable shell scripts should avoid
both -q and -s and should redirect standard and error output to
/dev/null instead. (-s is specified by POSIX.)
Output Line Prefix Control -b, –byte-offset Print the 0-based byte offset within the input file before each line of output. If -o (–only-matching) is specified, print the offset of the matching part itself.
-H, --with-filename
Print the file name for each match. This is the default when there
is more than one file to search.
-h, --no-filename
Suppress the prefixing of file names on output. This is the default
when there is only one file (or only standard input) to search.
--label=LABEL
Display input actually coming from standard input as input coming
from file LABEL. This is especially useful when implementing tools
like zgrep, e.g., gzip -cd foo.gz | grep --label=foo -H something.
See also the -H option.
-n, --line-number
Prefix each line of output with the 1-based line number within its
input file. (-n is specified by POSIX.)
-T, --initial-tab
Make sure that the first character of actual line content lies on a
tab stop, so that the alignment of tabs looks normal. This is useful
with options that prefix their output to the actual content: -H,-n,
and -b. In order to improve the probability that lines from a single
file will all start at the same column, this also causes the line
number and byte offset (if present) to be printed in a minimum size
field width.
-u, --unix-byte-offsets
Report Unix-style byte offsets. This switch causes grep to report
byte offsets as if the file were a 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.
-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.
Context Line Control -A NUM, –after-context=NUM Print NUM lines of trailing context after matching lines. Places a line containing a group separator (–) between contiguous groups of matches. With the -o or –only-matching option, this has no effect and a warning is given.
-B NUM, --before-context=NUM
Print NUM lines of leading context before matching lines. Places a
line containing a group separator (--) between contiguous groups of
matches. With the -o or --only-matching option, this has no effect
and a warning is given.
-C NUM, -NUM, --context=NUM
Print NUM lines of output context. Places a line containing a group
separator (--) between contiguous groups of matches. With the -o or
--only-matching option, this has no effect and a warning is given.
File and Directory Selection -a, –text Process a binary file as if it were text; this is equivalent to the –binary-files=text option.
--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.
-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, i.e., read directories just as if they were
ordinary files. If ACTION is skip, silently skip directories. If
ACTION is recurse, read all files under each directory, recursively,
following symbolic links only if they are on the command line. This
is equivalent to the -r option.
--exclude=GLOB
Skip files whose base name matches GLOB (using wildcard matching). A
file-name glob can use *, ?, and [...] as wildcards, and \ to quote
a wildcard or backslash character literally.
--exclude-from=FILE
Skip files whose base name matches any of the file-name globs read
from FILE (using wildcard matching as described under --exclude).
--exclude-dir=DIR
Exclude directories matching the pattern DIR from recursive searches.
-I Process a binary file as if it did not contain matching data; this is
equivalent to the --binary-files=without-match option.
--include=GLOB
Search only files whose base name matches GLOB (using wildcard
matching as described under --exclude).
-r, --recursive
Read all files under each directory, recursively, following symbolic
links only if they are on the command line. This is equivalent to
the -d recurse option.
-R, --dereference-recursive
Read all files under each directory, recursively. Follow all
symbolic links, unlike -r.
Other Options –line-buffered Use line buffering on output. This can cause a performance penalty.
-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 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.
-z, --null-data
Treat the input as a set of lines, each terminated by a zero byte
(the ASCII NUL character) instead of a newline. Like the -Z or
--null option, this option can be used with commands like sort -z to
process arbitrary file names.
REGULAR EXPRESSIONS A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions.
grep understands three different versions of regular expression syntax:
“basic,” “extended” and “perl.” In GNU grep, there is no difference in
available functionality between basic and extended syntaxes. In other
implementations, basic regular expressions are less powerful. The following
description applies to extended regular expressions; differences for basic
regular expressions are summarized afterwards. Perl regular expressions
give additional functionality, and are documented in pcresyntax(3) and
pcrepattern(3), but may not be available on every system.
The fundamental building blocks are the regular expressions that match a
single character. Most characters, including all letters and digits, are
regular expressions that match themselves. Any meta-character with special
meaning may be quoted by preceding it with a backslash.
The period . matches any single character.
Character Classes and Bracket Expressions 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
separated 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
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 the character class of numbers and letters in the current locale. In
the C locale and ASCII character set encoding, this is the same as
[0-9A-Za-z]. (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 expression.) Most meta-characters lose their special meaning
inside bracket expressions. 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.
Anchoring The caret ^ and the dollar sign $ are meta-characters that respectively match the empty string at the beginning and end of a line.
The Backslash Character and Special Expressions The symbols < 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. The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum:]].
Repetition 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. {,m} The preceding item is matched at most m times. This is a GNU extension. {n,m} The preceding item is matched at least n times, but not more than m times.
Concatenation Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated expressions.
Alternation Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either alternate expression.
Precedence Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole expression may be enclosed in parentheses to override these precedence rules and form a subexpression.
Back References and Subexpressions The back-reference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression.
Basic vs Extended Regular Expressions In basic regular expressions the meta-characters ?, +, {, |, (, and ) lose their special meaning; instead use the backslashed versions \?, +, {, |, (, and ).
Traditional egrep did not support the { meta-character, and some egrep
implementations support \{ instead, so portable scripts should avoid { in
grep -E patterns and should use [{] to match a literal {.
GNU grep -E 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 command grep -E '{1' searches for the two-character string {1
instead of reporting a syntax error in the regular expression. POSIX allows
this behavior as an extension, but portable scripts should avoid it.
ENVIRONMENT VARIABLES The behavior of grep is affected by the following environment variables.
The locale for category 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 the Brazilian Portuguese
locale is used for the LC_MESSAGES category. The C locale is used if none
of these environment variables are set, 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
This variable specifies the color used to highlight matched (non-
empty) text. It is deprecated in favor of GREP_COLORS, but still
supported. The mt, ms, and mc capabilities of GREP_COLORS have
priority over it. It can only specify the color used to highlight
the matching non-empty text in any matching line (a selected line
when the -v command-line option is omitted, or a context line when -v
is specified). The default is 01;31, which means a bold red
foreground text on the terminal's default background.
GREP_COLORS
Specifies the colors and other attributes used to highlight various
parts of the output. Its value is a colon-separated list of
capabilities that defaults to
ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36 with the rv and ne
boolean capabilities omitted (i.e., false). Supported capabilities
are as follows.
sl= SGR substring for whole selected lines (i.e., matching lines
when the -v command-line option is omitted, or non-matching
lines when -v is specified). If however the boolean rv
capability and the -v command-line option are both specified,
it applies to context matching lines instead. The default is
empty (i.e., the terminal's default color pair).
cx= SGR substring for whole context lines (i.e., non-matching
lines when the -v command-line option is omitted, or matching
lines when -v is specified). If however the boolean rv
capability and the -v command-line option are both specified,
it applies to selected non-matching lines instead. The
default is empty (i.e., the terminal's default color pair).
rv Boolean value that reverses (swaps) the meanings of the sl=
and cx= capabilities when the -v command-line option is
specified. The default is false (i.e., the capability is
omitted).
mt=01;31
SGR substring for matching non-empty text in any matching line
(i.e., a selected line when the -v command-line option is
omitted, or a context line when -v is specified). Setting
this is equivalent to setting both ms= and mc= at once to the
same value. The default is a bold red text foreground over
the current line background.
ms=01;31
SGR substring for matching non-empty text in a selected line.
(This is only used when the -v command-line option is
omitted.) The effect of the sl= (or cx= if rv) capability
remains active when this kicks in. The default is a bold red
text foreground over the current line background.
mc=01;31
SGR substring for matching non-empty text in a context line.
(This is only used when the -v command-line option is
specified.) The effect of the cx= (or sl= if rv) capability
remains active when this kicks in. The default is a bold red
text foreground over the current line background.
fn=35 SGR substring for file names prefixing any content line. The
default is a magenta text foreground over the terminal's
default background.
ln=32 SGR substring for line numbers prefixing any content line.
The default is a green text foreground over the terminal's
default background.
bn=32 SGR substring for byte offsets prefixing any content line.
The default is a green text foreground over the terminal's
default background.
se=36 SGR substring for separators that are inserted between
selected line fields (:), between context line fields, (-),
and between groups of adjacent lines when nonzero context is
specified (--). The default is a cyan text foreground over
the terminal's default background.
ne Boolean value that prevents clearing to the end of line using
Erase in Line (EL) to Right (\33[K) each time a colorized item
ends. This is needed on terminals on which EL is not
supported. It is otherwise useful on terminals for which the
back_color_erase (bce) boolean terminfo capability does not
apply, when the chosen highlight colors do not affect the
background, or when EL is too slow or causes too much flicker.
The default is false (i.e., the capability is omitted).
Note that boolean capabilities have no =... part. They are omitted
(i.e., false) by default and become true when specified.
See the Select Graphic Rendition (SGR) section in the documentation
of the text terminal that is used for permitted values and their
meaning as character attributes. These substring values are integers
in decimal representation and can be concatenated with semicolons.
grep takes care of assembling the result into a complete SGR sequence
(\33[...m). Common values to concatenate include 1 for bold, 4 for
underline, 5 for blink, 7 for inverse, 39 for default foreground
color, 30 to 37 for foreground colors, 90 to 97 for 16-color mode
foreground colors, 38;5;0 to 38;5;255 for 88-color and 256-color
modes foreground colors, 49 for default background color, 40 to 47
for background colors, 100 to 107 for 16-color mode background
colors, and 48;5;0 to 48;5;255 for 88-color and 256-color modes
background colors.
LC_ALL, LC_COLLATE, LANG
These variables specify the locale for the LC_COLLATE category, which
determines the collating sequence used to interpret range expressions
like [a-z].
LC_ALL, LC_CTYPE, LANG
These variables specify the locale for the LC_CTYPE category, which
determines the type of characters, e.g., which characters are
whitespace.
LC_ALL, LC_MESSAGES, LANG
These variables specify the locale for the LC_MESSAGES category,
which determines the language that grep uses for messages. The
default C locale uses American English messages.
POSIXLY_CORRECT
If set, grep behaves as POSIX requires; otherwise, grep behaves more
like other GNU programs. POSIX 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 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 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.
EXIT STATUS Normally, the 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. Note, however, that POSIX only mandates, for programs such as grep, cmp, and diff, that the exit status in case of error be greater than 1; it is therefore advisable, for the sake of portability, to use logic that tests for this general condition instead of strict equality with 2.
COPYRIGHT Copyright 1998-2000, 2002, 2005-2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
BUGS Reporting Bugs Email bug reports to bug-grep@gnu.org, a mailing list whose web page is http://lists.gnu.org/mailman/listinfo/bug-grep. grep’s Savannah bug tracker is located at http://savannah.gnu.org/bugs/?group=grep.
Known Bugs Large repetition counts in the {n,m} construct may cause grep to use lots of memory. In addition, certain other obscure regular expressions require exponential time and space, and may cause grep to run out of memory.
Back-references are very slow, and may require exponential time.
SEE ALSO Regular Manual Pages awk(1), cmp(1), diff(1), find(1), gzip(1), perl(1), sed(1), sort(1), xargs(1), zgrep(1), read(2), pcre(3), pcresyntax(3), pcrepattern(3), terminfo(5), glob(7), regex(7).
POSIX Programmer’s Manual Page grep(1p).
TeXinfo Documentation The full documentation for grep is maintained as a TeXinfo manual, which you can read at http://www.gnu.org/software/grep/manual/. If the info and grep programs are properly installed at your site, the command
info grep
should give you access to the complete manual.
NOTES This man page is maintained only fitfully; the full documentation is often more up-to-date.
GNU's not Unix, but Unix is a beast; its plural form is Unixen.
User Commands GNU grep 2.18 GREP(1)