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🔍 grep, egrep, fgrep, rgrep – print lines that match patterns

📖 NAME

grep, egrep, fgrep, rgrep — print lines that match patterns

🚀 Quick Reference

Use Case	Command	Description
🔍 Basic search	grep 'pattern' file	Print lines matching pattern in a file.
🔍 Case-insensitive	grep -i 'pattern' file	Ignore case when matching.
🔍 Recursive search	grep -r 'pattern' dir/	Search recursively through directories.
🔍 Invert match	grep -v 'pattern' file	Print lines that do NOT match.
🔍 Count matches	grep -c 'pattern' file	Print count of matching lines per file.
🔍 Show line numbers	grep -n 'pattern' file	Prefix each output line with its line number.
🔍 Only matching text	grep -o 'pattern' file	Print only the matched parts of a line.
🔍 Context lines	grep -C 3 'pattern' file	Show 3 lines of context before and after match.
🔍 Fixed strings (no regex)	grep -F 'literal' file	Treat pattern as fixed string, not regex.
🔍 Extended regex (ERE)	grep -E 'pattern' file	Use extended regular expressions.
🔍 Perl-compatible regex (PCRE)	grep -P 'pattern' file	Use Perl-compatible regular expressions.
🔍 Binary files as text	grep -a 'pattern' file	Treat binary file as text.
🔍 Max count	grep -m 5 'pattern' file	Stop after finding 5 matches.
🔍 Quiet (silent)	grep -q 'pattern' file	Exit immediately if match found (no output).
🔍 Exclude files	grep --exclude='*.log' 'pattern' .	Skip files matching glob pattern.

🔧 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

ℹ️ 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 -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.
• --no-ignore-case — Do not ignore case distinctions. This is the default. Useful for overriding -i in shell scripts.
• -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. Word-constituent characters are letters, digits, and underscore. 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 -v, 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 with escape sequences to display them in color on the terminal. 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 stops upon 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, ensures the standard input is positioned to just after the last matching line before exiting. When -c or --count is also used, does not output a count greater than NUM. When -v is also used, stops after 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.
• -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 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 coming from standard input as coming from file LABEL. 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 -H.
• -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. Useful with options that prefix their output to the actual content: -H, -n, and -b.
• -Z, --null — Output a zero byte (ASCII NUL) instead of the character that normally follows a file name. For example, grep -lZ outputs a zero byte after each file name. This option makes the output unambiguous, even in the presence of file names containing unusual characters like newlines. Can be used with commands like find -print0, perl -0, sort -z, and xargs -0.

📐 Context Line Control

• -A NUM, --after-context=NUM — Print NUM lines of trailing context after matching lines. Places a group separator (--) between contiguous groups of matches. With -o or --only-matching, 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 group separator (--) between contiguous groups of matches. With -o or --only-matching, this has no effect and a warning is given.
• -C NUM, -NUM, --context=NUM — Print NUM lines of output context. Places a group separator (--) between contiguous groups of matches. With -o or --only-matching, 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; equivalent to --binary-files=text.
• --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. 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. If TYPE is without-match, when grep discovers null input binary data it assumes that the rest of the file does not match; equivalent to -I. If TYPE is text, grep processes a binary file as if it were text; equivalent to -a.
• -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. Equivalent to -r.
• --exclude=GLOB — Skip any command-line file with a name suffix that matches the pattern GLOB, using wildcard matching. When searching recursively, skip any subfile whose base name matches GLOB. 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.
• -I — Process a binary file as if it did not contain matching data; equivalent to --binary-files=without-match.
• --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. Equivalent to -d recurse.
• -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. Specifying -U overrules this guesswork, causing all files to be read and passed to the matching mechanism verbatim. 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 (ASCII NUL) 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 pcresyntax(3) and pcrepattern(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. 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: [: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]. 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. (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
• 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_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. 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. Default empty.
• cx= — SGR substring for whole context lines. Default empty.
• rv — Boolean that reverses (swaps) the meanings of sl= and cx= when -v is specified. Default false.
• mt=01;31 — SGR substring for matching non-empty text in any matching line. Default bold red.
• ms=01;31 — SGR substring for matching non-empty text in a selected line. Default bold red.
• mc=01;31 — SGR substring for matching non-empty text in a context line. Default bold red.
• fn=35 — SGR substring for file names. Default magenta.
• ln=32 — SGR substring for line numbers. Default green.
• bn=32 — SGR substring for byte offsets. Default green.
• se=36 — SGR substring for separators. Default cyan.
• ne — Boolean that prevents clearing to the end of line using Erase in Line (EL) to Right. Default false.

Note that boolean capabilities have no =... part. They are omitted (i.e., false) by default and become true when specified.

🌍 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.

🌍 LC_ALL, LC_MESSAGES, LANG

These variables specify the locale for the LC_MESSAGES category, which determines the language that grep uses for 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 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. 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

Copyright 1998-2000, 2002, 2005-2021 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 AT 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.
• 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), pcre(3), pcresyntax(3), pcrepattern(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.

🔍 grep, egrep, fgrep, rgrep – print lines that match patterns 📖 NAME 🚀 Quick Reference 🔧 SYNOPSIS 📝 DESCRIPTION ⚙️ OPTIONS 🔍 REGULAR EXPRESSIONS 🚪 Exit Status 🌐 ENVIRONMENT 📝 NOTES ©️ COPYRIGHT 🐛 BUGS 💡 EXAMPLE 📚 SEE ALSO