grep, egrep, fgrep, rgrep - 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 patterns separated by newline characters, and
grep prints each line that matches a pattern.
A FILE of “-” stands for standard
input. If no FILE is given, recursive searches examine the working
directory, and nonrecursive searches read standard input.
In addition, the variant programs egrep, fgrep and
rgrep are the same as grep -E, grep -F,
and grep -r, respectively. These variants are deprecated, but
are provided for backward compatibility.
- --help
- Output a usage message and exit.
- -V, --version
- Output the version number of grep and exit.
- -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.
- -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.
- -i,
--ignore-case
- Ignore case distinctions, so that characters that differ only in case
match 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 $.
- -y
- Obsolete synonym for -i.
- -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.
- --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.
- -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.
- -s,
--no-messages
- Suppress error messages about nonexistent or unreadable files.
- -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.
- -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.
- -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.
- -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 when grep discovers
that a file is binary it suppresses any further output, and instead
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, when grep discovers that a
file is binary 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 any suffix starting after a / and before a non-/.
When searching recursively, skip any subfile whose base name matches
GLOB; the base name is the part after the last /. 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).
- -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.
- --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 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-compatible
regular expressions give additional functionality, and are documented in
pcresyntax(3) and pcrepattern(3), but work only if PCRE is available in the
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. It is
unspecified whether it matches an encoding error.
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. 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.
The caret ^ and the dollar sign $ are
meta-characters that respectively match the empty string at the beginning
and end of a line.
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:]].
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.
Two regular expressions may be concatenated; the resulting regular
expression matches any string formed by concatenating two substrings that
respectively match the concatenated expressions.
Two regular expressions may be joined by the infix operator
|; the resulting regular expression matches any string matching
either alternate expression.
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.
The back-reference \n, where n is a single
digit, matches the substring previously matched by the nth
parenthesized subexpression of the regular expression.
In basic regular expressions the meta-characters ?,
+, {, |, (, and ) lose their special
meaning; instead use the backslashed versions \?, \+,
\{, \|, \(, and \).
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_OPTIONS
- This variable specifies default options to be placed in front of any
explicit options. As this causes problems when writing portable scripts,
this feature will be removed in a future release of grep, and
grep warns if it is used. Please use an alias or script
instead.
- 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.
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”.
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.
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.
Copyright 1998–2000, 2002, 2005–2018 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.
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.
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.
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).
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 man page is maintained only fitfully; the full documentation
is often more up-to-date.