|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | REGULAR EXPRESSIONS | EXIT STATUS | ENVIRONMENT | NOTES | COPYRIGHT | BUGS | EXAMPLE | SEE ALSO | COLOPHON |
|
|
|
GREP(1) User Commands GREP(1)
grep - print lines that match patterns
grep [OPTION...] PATTERNS [FILE...]
grep [OPTION...] -e PATTERNS ... [FILE...]
grep [OPTION...] -f PATTERN_FILE ... [FILE...]
grep searches for PATTERNS in each FILE. PATTERNS is one or more
patterns separated by newline characters, and grep prints each
line that matches a pattern. Typically PATTERNS should be quoted
when grep is used in a shell command.
A FILE of “-” stands for standard input. If no FILE is given,
recursive searches examine the working directory, and
nonrecursive searches read standard input.
Generic Program Information
--help Output a usage message and exit.
-V, --version
Output the version number of grep and exit.
Pattern Syntax
-E, --extended-regexp
Interpret PATTERNS as extended regular expressions (EREs,
see below).
-F, --fixed-strings
Interpret PATTERNS as fixed strings, not regular
expressions.
-G, --basic-regexp
Interpret PATTERNS as basic regular expressions (BREs, see
below). This is the default.
-P, --perl-regexp
Interpret PATTERNS as Perl-compatible regular expressions
(PCREs). This option is experimental when combined with
the -z (--null-data) option, and grep -P may warn of
unimplemented features.
Matching Control
-e PATTERNS, --regexp=PATTERNS
Use PATTERNS as the patterns. If this option is used
multiple times or is combined with the -f (--file) option,
search for all patterns given. This option can be used to
protect a pattern beginning with “-”.
-f FILE, --file=FILE
Obtain patterns from FILE, one per line. If this option
is used multiple times or is combined with the -e
(--regexp) option, search for all patterns given. The
empty file contains zero patterns, and therefore matches
nothing. If FILE is - , read patterns from standard
input.
-i, --ignore-case
Ignore case distinctions in patterns and input data, so
that characters that differ only in case match each other.
--no-ignore-case
Do not ignore case distinctions in patterns and input
data. This is the default. This option is useful for
passing to shell scripts that already use -i, to cancel
its effects because the two options override each other.
-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 character. Word-constituent characters are
letters, digits, and the underscore. This option has no
effect if -x is also specified.
-x, --line-regexp
Select only those matches that exactly match the whole
line. For a regular expression pattern, this is like
parenthesizing the pattern and then surrounding it with ^
and $.
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 above), count non-matching lines.
--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. 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.
-l, --files-with-matches
Suppress normal output; instead print the name of each
input file from which output would normally have been
printed. Scanning each input file stops upon first match.
-m NUM, --max-count=NUM
Stop reading a file after NUM matching lines. If NUM is
zero, grep stops right away without reading input. A NUM
of -1 is treated as infinity and grep does not stop; this
is the default. 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.
-s, --no-messages
Suppress error messages about nonexistent or unreadable
files.
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. This is a GNU
extension.
-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 can be useful for commands
that transform a file's contents before searching, e.g.,
gzip -cd foo.gz | grep --label=foo -H 'some pattern'. See
also the -H option.
-n, --line-number
Prefix each line of output with the 1-based line number
within its input file.
-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.
-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.
--group-separator=SEP
When -A, -B, or -C are in use, print SEP instead of --
between groups of lines.
--no-group-separator
When -A, -B, or -C are in use, do not print a separator
between groups of lines.
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 a file's data or metadata indicate that the file
contains binary data, assume that the file is of type
TYPE. Non-text bytes indicate binary data; these are
either output bytes that are improperly encoded for the
current locale, or null input bytes when the -z option is
not given.
By default, TYPE is binary, and grep suppresses output
after null input binary data is discovered, and suppresses
output lines that contain improperly encoded data. When
some output is suppressed, grep follows any output with a
message to standard error saying that a binary file
matches.
If TYPE is without-match, when grep discovers null input
binary data it assumes that the rest of the 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.
When type is binary, grep may treat non-text bytes as line
terminators even without the -z option. This means
choosing binary versus text can affect whether a pattern
matches a file. For example, when type is binary the
pattern q$ might match q immediately followed by a null
byte, even though this is not matched when type is text.
Conversely, when type is binary the pattern . (period)
might not match a null byte.
Warning: The -a option 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. On the other hand, when reading files whose
text encodings are unknown, it can be helpful to use -a or
to set LC_ALL='C' in the environment, in order to find
more matches even if the matches are unsafe for direct
display.
-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 any command-line file with a name suffix that matches
the pattern GLOB, using wildcard matching; a name suffix
is either the whole name, or a trailing part that starts
with a non-slash character immediately after a slash (/)
in the name. When searching recursively, skip any subfile
whose base name matches GLOB; the base name is the part
after the last slash. A pattern 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=GLOB
Skip any command-line directory with a name suffix that
matches the pattern GLOB. When searching recursively,
skip any subdirectory whose base name matches GLOB.
Ignore any redundant trailing slashes in GLOB.
-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). If
contradictory --include and --exclude options are given,
the last matching one wins. If no --include or --exclude
options match, a file is included unless the first such
option is --include.
-r, --recursive
Read all files under each directory, recursively,
following symbolic links only if they are on the command
line. Note that if no file operand is given, grep
searches the working directory. 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 whether a file is text or binary
as described for the --binary-files option. 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 input and output data as sequences 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.
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” (PCRE). In
GNU grep, basic and extended regular expressions are merely
different notations for the same pattern-matching functionality.
In other implementations, basic regular expressions are
ordinarily less powerful than extended, though occasionally it is
the other way around. The following description applies to
extended regular expressions; differences for basic regular
expressions are summarized afterwards. Perl-compatible regular
expressions have different functionality, and are documented in
pcre2syntax(3) and pcre2pattern(3), but work only if PCRE support
is enabled.
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. It is unspecified
whether it matches an encoding error.
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; it is unspecified whether it matches
an encoding error. 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. In the default C locale, it
matches any single character that appears between the two
characters in ASCII order, inclusive. For example, [a-d] is
equivalent to [abcd]. In other locales the behavior is
unspecified: [a-d] might be equivalent to [abcd] or [aBbCcDd] or
some other bracket expression, or it might fail to match any
character, or the set of characters that it matches might be
erratic, or it might be invalid. 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:], [:blank:],
[: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 \?, \+, \{, \|, \(, and \).
Normally the exit status is 0 if a line is selected, 1 if no
lines were selected, and 2 if an error occurred. However, if the
-q or --quiet or --silent is used and a line is selected, the
exit status is 0 even if an error occurred.
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). The shell command locale -a lists locales that
are currently available.
GREP_COLORS
Controls how the --color option highlights 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. This category also
determines the character encoding, that is, whether text
is encoded in UTF-8, ASCII, or some other encoding. In
the C or POSIX locale, all characters are encoded as a
single byte and every byte is a valid character.
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”.
This man page is maintained only fitfully; the full documentation
is often more up-to-date.
Copyright 1998–2000, 2002, 2005–2024 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.
Reporting Bugs
Email bug reports to the bug-reporting address ⟨bug-
grep@gnu.org⟩. An email archive
⟨https://lists.gnu.org/mailman/listinfo/bug-grep⟩ and a bug
tracker ⟨https://debbugs.gnu.org/cgi/pkgreport.cgi?package=grep⟩
are available.
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.
The following example outputs the location and contents of any
line containing “f” and ending in “.c”, within all files in the
current directory whose names contain “g” and end in “.h”. The
-n option outputs line numbers, the -- argument treats expansions
of “*g*.h” starting with “-” as file names not options, and the
empty file /dev/null causes file names to be output even if only
one file name happens to be of the form “*g*.h”.
$ grep -n -- 'f.*\.c$' *g*.h /dev/null
argmatch.h:1:/* definitions and prototypes for argmatch.c
The only line that matches is line 1 of argmatch.h. Note that
the regular expression syntax used in the pattern differs from
the globbing syntax that the shell uses to match file names.
Regular Manual Pages
awk(1), cmp(1), diff(1), find(1), perl(1), sed(1), sort(1),
xargs(1), read(2), pcre2(3), pcre2syntax(3), pcre2pattern(3),
terminfo(5), glob(7), regex(7)
Full Documentation
A complete manual ⟨https://www.gnu.org/software/grep/manual/⟩ is
available. If the info and grep programs are properly installed
at your site, the command
info grep
should give you access to the complete manual.
This page is part of the GNU grep (regular expression file search
tool) project. Information about the project can be found at
⟨https://www.gnu.org/software/grep/⟩. If you have a bug report
for this manual page, send it to bug-grep@gnu.org. This page was
obtained from the project's upstream Git repository
⟨git://git.savannah.gnu.org/grep.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
GNU grep 3.11.30-53b8-dirty 2019-12-29 GREP(1)
Pages that refer to this page: git-grep(1), look(1), pmrep(1), sed(1), stap(1), regex(3), regex(7), bridge(8), ip(8), tc(8)
|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|