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.

Installation

USE flags

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

nls Add Native Language Support (using gettextGNU 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

Emerge

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.

Invocation

user $cmd --help
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/>

Unmerge

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

See also

  • ed — a line-based text editor with support for regular expressions
  • sed — a program that uses regular expressions to programmatically modify streams of text
  • awk — a scripting language for data extraction
  • Perl — a general purpose interpreted programming language with a powerful regular expression engine.
  • Raku — a high-level, general-purpose, and gradually typed programming language.