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Manual Pages  — GREP

NAME

grep, egrep, fgrep, rgrep – file pattern searcher

CONTENTS

SYNOPSIS


grep [-abcdDEFGHhIiLlmnOopqRSsUVvwxz] [-A num] [-B num] [-C [num]] [-e pattern] [-f file] [-binary-files= value] [-color [ =when]] [-colour [ =when]] [-context [ =num]] [-label] [-line-buffered] [-null] [pattern] [file ...]

DESCRIPTION

The grep utility searches any given input files, selecting lines that match one or more patterns. By default, a pattern matches an input line if the regular expression (RE) in the pattern matches the input line without its trailing newline. An empty expression matches every line. Each input line that matches at least one of the patterns is written to the standard output.

grep is used for simple patterns and basic regular expressions (BREs); egrep can handle extended regular expressions (EREs). See re_format(7) for more information on regular expressions. fgrep is quicker than both grep and egrep, but can only handle fixed patterns (i.e., it does not interpret regular expressions). Patterns may consist of one or more lines, allowing any of the pattern lines to match a portion of the input.

The following options are available:
-A num , -after-context= num
  Print num lines of trailing context after each match. See also the -B and -C options.
-a -, -text
  Treat all files as ASCII text. Normally grep will simply print "Binary file ... matches" if files contain binary characters. Use of this option forces grep to output lines matching the specified pattern.
-B num , -before-context= num
  Print num lines of leading context before each match. See also the -A and -C options.
-b -, -byte-offset
  The offset in bytes of a matched pattern is displayed in front of the respective matched line.
-C [num ], -context [=num ]
  Print num lines of leading and trailing context surrounding each match. The default value of num is "2" and is equivalent to "-A 2 -B 2". Note: no whitespace may be given between the option and its argument.
-c -, -count
  Only a count of selected lines is written to standard output.
-colour= [when ], -color= [when ]
  Mark up the matching text with the expression stored in the GREP_COLOR environment variable. The possible values of when are " never", " always" and " auto".
-D action , -devices= action
  Specify the demanded action for devices, FIFOs and sockets. The default action is " read", which means, that they are read as if they were normal files. If the action is set to " skip", devices are silently skipped.
-d action , -directories= action
  Specify the demanded action for directories. It is " read" by default, which means that the directories are read in the same manner as normal files. Other possible values are " skip" to silently ignore the directories, and " recurse" to read them recursively, which has the same effect as the -R and -r option.
-E -, -extended-regexp
  Interpret pattern as an extended regular expression (i.e., force grep to behave as egrep).
-e pattern , -regexp= pattern
  Specify a pattern used during the search of the input: an input line is selected if it matches any of the specified patterns. This option is most useful when multiple -e options are used to specify multiple patterns, or when a pattern begins with a dash ('-').
-exclude pattern
  If specified, it excludes files matching the given filename pattern from the search. Note that -exclude and -include patterns are processed in the order given. If a name matches multiple patterns, the latest matching rule wins. If no -include pattern is specified, all files are searched that are not excluded. Patterns are matched to the full path specified, not only to the filename component.
-exclude-dir pattern
  If -R is specified, it excludes directories matching the given filename pattern from the search. Note that -exclude-dir and -include-dir patterns are processed in the order given. If a name matches multiple patterns, the latest matching rule wins. If no -include-dir pattern is specified, all directories are searched that are not excluded.
-F -, -fixed-strings
  Interpret pattern as a set of fixed strings (i.e., force grep to behave as fgrep).
-f file , -file= file
  Read one or more newline separated patterns from file. Empty pattern lines match every input line. Newlines are not considered part of a pattern. If file is empty, nothing is matched.
-G -, -basic-regexp
  Interpret pattern as a basic regular expression (i.e., force grep to behave as traditional grep).
-H
  Always print filename headers with output lines.
-h -, -no-filename
  Never print filename headers (i.e., filenames) with output lines.
-help
  Print a brief help message.
-I
  Ignore binary files. This option is equivalent to the "-binary-file= without-match" option.
-i -, -ignore-case
  Perform case insensitive matching. By default, grep is case sensitive.
-include pattern
  If specified, only files matching the given filename pattern are searched. Note that -include and -exclude patterns are processed in the order given. If a name matches multiple patterns, the latest matching rule wins. Patterns are matched to the full path specified, not only to the filename component.
-include-dir pattern
  If -R is specified, only directories matching the given filename pattern are searched. Note that -include-dir and -exclude-dir patterns are processed in the order given. If a name matches multiple patterns, the latest matching rule wins.
-L -, -files-without-match
  Only the names of files not containing selected lines are written to standard output. Pathnames are listed once per file searched. If the standard input is searched, the string "(standard input)" is written unless a -label is specified.
-l -, -files-with-matches
  Only the names of files containing selected lines are written to standard output. grep will only search a file until a match has been found, making searches potentially less expensive. Pathnames are listed once per file searched. If the standard input is searched, the string "(standard input)" is written unless a -label is specified.
-label
  Label to use in place of "(standard input)" for a file name where a file name would normally be printed. This option applies to -H, -L, and -l.
-mmap
  Use mmap(2) instead of read(2) to read input, which can result in better performance under some circumstances but can cause undefined behaviour.
-m num , -max-count= num
  Stop reading the file after num matches.
-n -, -line-number
  Each output line is preceded by its relative line number in the file, starting at line 1. The line number counter is reset for each file processed. This option is ignored if -c, -L, -l, or -q is specified.
-null
  Prints a zero-byte after the file name.
-O
  If -R is specified, follow symbolic links only if they were explicitly listed on the command line. The default is not to follow symbolic links.
-o -, -only-matching
  Prints only the matching part of the lines.
-p
  If -R is specified, no symbolic links are followed. This is the default.
-q -, -quiet -, -silent
  Quiet mode: suppress normal output. grep will only search a file until a match has been found, making searches potentially less expensive.
-R -, -r -, -recursive
  Recursively search subdirectories listed. (i.e., force grep to behave as rgrep).
-S
  If -R is specified, all symbolic links are followed. The default is not to follow symbolic links.
-s -, -no-messages
  Silent mode. Nonexistent and unreadable files are ignored (i.e., their error messages are suppressed).
-U -, -binary
  Search binary files, but do not attempt to print them.
-u
  This option has no effect and is provided only for compatibility with GNU grep.
-V -, -version
  Display version information and exit.
-v -, -invert-match
  Selected lines are those not matching any of the specified patterns.
-w -, -word-regexp
  The expression is searched for as a word (as if surrounded by '[[:<:]]' and '[[:>:]]'; see re_format(7)).
-x -, -line-regexp
  Only input lines selected against an entire fixed string or regular expression are considered to be matching lines.
-y
  Equivalent to -i. Obsoleted.
-z -, -null-data
  Treat input and output data as sequences of lines terminated by a zero-byte instead of a newline.
-binary-files= value
  Controls searching and printing of binary files. Options are:
binary (default) Search binary files but do not print them.
without-match Do not search binary files.
text Treat all files as text.
-line-buffered Force output to be line buffered. By default, output is line buffered when standard output is a terminal and block buffered otherwise.

If no file arguments are specified, the standard input is used. Additionally, " -" may be used in place of a file name, anywhere that a file name is accepted, to read from standard input. This includes both -f and file arguments.

EXIT STATUS

The grep utility exits with one of the following values:

0 One or more lines were selected.
1 No lines were selected.
>1 An error occurred.

EXAMPLES

To find all occurrences of the word 'patricia' in a file:

    $ grep 'patricia' myfile

To find all occurrences of the pattern ‘.Pp’ at the beginning of a line:

    $ grep '^\.Pp' myfile

The apostrophes ensure the entire expression is evaluated by grep instead of by the user's shell. The caret ‘^’ matches the null string at the beginning of a line, and the ‘\’ escapes the ‘.’, which would otherwise match any character.

To find all lines in a file which do not contain the words 'foo' or 'bar':

    $ grep -v -e 'foo' -e 'bar' myfile

A simple example of an extended regular expression:

    $ egrep '19|20|25' calendar

Peruses the file 'calendar' looking for either 19, 20, or 25.

SEE ALSO

ed(1), ex(1), sed(1), zgrep(1), re_format(7)

STANDARDS

The grep utility is compliant with the IEEE Std 1003.1-2008 ("POSIX.1") specification.

The flags [-AaBbCDdGHhILmoPRSUVw] are extensions to that specification, and the behaviour of the -f flag when used with an empty pattern file is left undefined.

All long options are provided for compatibility with GNU versions of this utility.

Historic versions of the grep utility also supported the flags [-ruy]. This implementation supports those options; however, their use is strongly discouraged.

HISTORY

The grep command first appeared in AT&T v6 .

GREP (1) August 7, 2020

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