Provided by: grep_3.11-4build1_amd64 
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 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.
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 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.