grep

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grep is a tool for searching text files with regular expressions. Its name is a play on the ed command g/re/p which would globally search a document for a given regular expression and print the results.

There are multiple implementations of grep. By default, Gentoo installs GNU Grep (sys-apps/grep), as part of the @system set. GNU Grep can be configured to behave as required by POSIX via the POSIXLY_CORRECT environment variable; refer to the GNU grep(1) man page for further information.

Installation

USE flags

USE flags for sys-apps/grep GNU regular expression matcher

`+egrep-fgrep`	Install deprecated 'egrep' and 'fgrep' wrappers for 'grep -E' and 'grep -F' respectively. GNU grep 3.8 onwards warns about their usage by default, but the versions installed by this flag do not. No deprecation warnings are emitted when this flag is enabled.
`nls`	Add Native Language Support (using gettext - GNU locale utilities)
`pcre`	Add support for Perl Compatible Regular Expressions
`static`	!!do not set this during bootstrap!! Causes binaries to be statically linked instead of dynamically
`verify-sig`	Verify upstream signatures on distfiles

Data provided by the Gentoo Package Database · Last update: 2025-04-10 17:50 More information about USE flags

Emerge

Install sys-apps/grep:

root #emerge --ask sys-apps/grep

Configuration

Environment variables

GREP_COLOR (deprecated) colorizes matching text, by default this is set to 01;31 which is a bold red.
GREP_COLORS sets the color of various parts of output, not just matches.
LC_ALL, LC_COLLATE, LANG specify the locale for the collating sequence.
LC_ALL, LC_CTYPE, LANG determines the encoding of characters and their attributes.
LC_ALL, LC_MESSAGES, LANG determines the language grep uses for messages.
POSIXLY_CORRECT treat all input after a file name as an additional file name among other things.

Usage

See also
For more information see devmanual.

Invocation

To see grep usage information:

user $grep --help

Expand

Usage: grep [OPTION]... PATTERNS [FILE]...
Search for PATTERNS in each FILE.
Example: grep -i 'hello world' menu.h main.c
PATTERNS can contain multiple patterns separated by newlines.

Pattern selection and interpretation:
  -E, --extended-regexp     PATTERNS are extended regular expressions
  -F, --fixed-strings       PATTERNS are strings
  -G, --basic-regexp        PATTERNS are basic regular expressions
  -P, --perl-regexp         PATTERNS are Perl regular expressions
  -e, --regexp=PATTERNS     use PATTERNS for matching
  -f, --file=FILE           take PATTERNS from FILE
  -i, --ignore-case         ignore case distinctions in patterns and data
      --no-ignore-case      do not ignore case distinctions (default)
  -w, --word-regexp         match only whole words
  -x, --line-regexp         match only whole lines
  -z, --null-data           a data line ends in 0 byte, not newline

Miscellaneous:
  -s, --no-messages         suppress error messages
  -v, --invert-match        select non-matching lines
  -V, --version             display version information and exit
      --help                display this help text and exit

Output control:
  -m, --max-count=NUM       stop after NUM selected lines
  -b, --byte-offset         print the byte offset with output lines
  -n, --line-number         print line number with output lines
      --line-buffered       flush output on every line
  -H, --with-filename       print file name with output lines
  -h, --no-filename         suppress the file name prefix on output
      --label=LABEL         use LABEL as the standard input file name prefix
  -o, --only-matching       show only nonempty parts of lines that match
  -q, --quiet, --silent     suppress all normal output
      --binary-files=TYPE   assume that binary files are TYPE;
                            TYPE is 'binary', 'text', or 'without-match'
  -a, --text                equivalent to --binary-files=text
  -I                        equivalent to --binary-files=without-match
  -d, --directories=ACTION  how to handle directories;
                            ACTION is 'read', 'recurse', or 'skip'
  -D, --devices=ACTION      how to handle devices, FIFOs and sockets;
                            ACTION is 'read' or 'skip'
  -r, --recursive           like --directories=recurse
  -R, --dereference-recursive  likewise, but follow all symlinks
      --include=GLOB        search only files that match GLOB (a file pattern)
      --exclude=GLOB        skip files that match GLOB
      --exclude-from=FILE   skip files that match any file pattern from FILE
      --exclude-dir=GLOB    skip directories that match GLOB
  -L, --files-without-match  print only names of FILEs with no selected lines
  -l, --files-with-matches  print only names of FILEs with selected lines
  -c, --count               print only a count of selected lines per FILE
  -T, --initial-tab         make tabs line up (if needed)
  -Z, --null                print 0 byte after FILE name

Context control:
  -B, --before-context=NUM  print NUM lines of leading context
  -A, --after-context=NUM   print NUM lines of trailing context
  -C, --context=NUM         print NUM lines of output context
  -NUM                      same as --context=NUM
      --group-separator=SEP  print SEP on line between matches with context
      --no-group-separator  do not print separator for matches with context
      --color[=WHEN],
      --colour[=WHEN]       use markers to highlight the matching strings;
                            WHEN is 'always', 'never', or 'auto'
  -U, --binary              do not strip CR characters at EOL (MSDOS/Windows)

When FILE is '-', read standard input.  With no FILE, read '.' if
recursive, '-' otherwise.  With fewer than two FILEs, assume -h.
Exit status is 0 if any line is selected, 1 otherwise;
if any error occurs and -q is not given, the exit status is 2.

Report bugs to: bug-grep@gnu.org
GNU grep home page: <https://www.gnu.org/software/grep/>
General help using GNU software: <https://www.gnu.org/gethelp/>

Removal

Unmerge

Remove sys-apps/grep:

root #emerge --ask --depclean --verbose sys-apps/grep