GREP(1) User Commands GREP(1)
NAME
grep, egrep, fgrep, rgrep - print lines that match patterns
SYNOPSIS
grep [OPTION...] PATTERNS [FILE...]
grep [OPTION...] -e PATTERNS ... [FILE...]
grep [OPTION...] -f PATTERN_FILE ... [FILE...]
DESCRIPTION
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.
Debian also includes the variant programs egrep, fgrep and rgrep. These
programs are the same as grep -E, grep -F, and grep -r, respectively.
These variants are deprecated upstream, but Debian provides for backward
compatibility. For portability reasons, it is recommended to avoid the
variant programs, and use grep with the related option instead.
OPTIONS
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.
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” (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. 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:], [: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 \?, \+,
\{, \|, \(, and \).
EXIT STATUS
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.
ENVIRONMENT
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”.
NOTES
This man page is maintained only fitfully; the full documentation is
often more up-to-date.
COPYRIGHT
Copyright 1998-2000, 2002, 2005-2023 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 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.
EXAMPLE
The following example outputs the location and contents of any line con-
taining “f” and ending in “.c”, within all files in the current directo-
ry 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 regu-
lar expression syntax used in the pattern differs from the globbing syn-
tax that the shell uses to match file names.
SEE ALSO
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 avail-
able. If the info and grep programs are properly installed at your
site, the command
info grep
should give you access to the complete manual.
GNU grep 3.11 2019-12-29 GREP(1)
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