GREP

Section: User Commands (1)
Updated: 2019-12-29
Index Return to Main Contents

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.

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.

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.
-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 $.
-y: Obsolete synonym for -i.

General Output Control

-c, --count: Suppress normal output; instead print a count of matching lines for each input file. With the -v, --invert-match option (see below), count non-matching lines.
--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.

Output Line Prefix Control

-b, --byte-offset: Print the 0-based byte offset within the input file before each line of output. If -o (--only-matching) is specified, print the offset of the matching part itself.
-H, --with-filename: Print the file name for each match. This is the default when there is more than one file to search.
-h, --no-filename: Suppress the prefixing of file names on output. This is the default when there is only one file (or only standard input) to search.
--label=LABEL: Display input actually coming from standard input as input coming from file LABEL. This 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.
-u, --unix-byte-offsets: Report Unix-style byte offsets. This switch causes grep to report byte offsets as if the file were a Unix-style text file, i.e., with CR characters stripped off. This will produce results identical to running grep on a Unix machine. This option has no effect unless -b option is also used; it has no effect on platforms other than MS-DOS and MS-Windows.
-Z, --null: Output a zero byte (the ASCII NUL character) instead of the character that normally follows a file name. For example, grep -lZ outputs a zero byte after each file name instead of the usual newline. This option makes the output unambiguous, even in the presence of file names containing unusual characters like newlines. This option can be used with commands like find -print0, perl -0, sort -z, and xargs -0 to process arbitrary file names, even those that contain newline characters.

Context Line Control

-A NUM, --after-context=NUM: Print NUM lines of trailing context after matching lines. Places a line containing a group separator (--) between contiguous groups of matches. With the -o or --only-matching option, this has no effect and a warning is given.
-B NUM, --before-context=NUM: Print NUM lines of leading context before matching lines. Places a line containing a group separator (--) between contiguous groups of matches. With the -o or --only-matching option, this has no effect and a warning is given.
-C NUM, -NUM, --context=NUM: Print NUM lines of output context. Places a line containing a group separator (--) between contiguous groups of matches. With the -o or --only-matching option, this has no effect and a warning is given.

File and Directory Selection

-a, --text: Process a binary file as if it were text; this is equivalent to the --binary-files=text option.
--binary-files=TYPE: If 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 one-line message 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).
-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 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 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.

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_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.

NOTES

This man page is maintained only fitfully; the full documentation is often more up-to-date.

COPYRIGHT

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 An email archive and a bug tracker 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.