NAME¶
grep, egrep, fgrep, rgrep - 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, three variant programs
egrep, fgrep and
rgrep
are available.
egrep is the same as
grep -E.
fgrep
is the same as
grep -F.
rgrep is the same as
grep -r. Direct invocation as either
egrep or
fgrep
is deprecated, but is provided to allow historical applications that rely on
them to run unmodified.
OPTIONS¶
- --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
(PCRE, see below). 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, 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.
- --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, -r, --recursive
- Read all files under each directory, recursively; this is
equivalent to the -d recurse option.
Other Options¶
- --line-buffered
- Use line buffering on output. This can cause a performance
penalty.
- --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.
- -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” (BRE), “extended” (ERE) and “perl”
(PRCE). 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.
- {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.2 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.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 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¶
The exit status is 0 if selected lines are found, and 1 if not found. If an
error occurred the exit status is 2. (Note: POSIX error handling code should
check for '2' or greater.)
COPYRIGHT¶
Copyright 1998-2000, 2002, 2005-2012 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),
mmap(2),
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. 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¶
GNU's not Unix, but Unix is a beast; its plural form is Unixen.