grep: grep Programs
2.4 ‘grep’ Programs
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‘grep’ searches the named input files for lines containing a match to
the given pattern. By default, ‘grep’ prints the matching lines. A
file named ‘-’ stands for standard input. If no input is specified,
‘grep’ searches the working directory ‘.’ if given a command-line option
specifying recursion; otherwise, ‘grep’ searches standard input. There
are four major variants of ‘grep’, controlled by the following options.
‘-G’
‘--basic-regexp’
Interpret the pattern as a basic regular expression (BRE). This is
the default.
‘-E’
‘--extended-regexp’
Interpret the pattern as an extended regular expression (ERE).
(‘-E’ is specified by POSIX.)
‘-F’
‘--fixed-strings’
Interpret the pattern as a list of fixed strings (instead of
regular expressions), separated by newlines, any of which is to be
matched. (‘-F’ is specified by POSIX.)
‘-P’
‘--perl-regexp’
Interpret the pattern as a Perl-compatible regular expression
(PCRE). This is experimental, particularly when combined with the
‘-z’ (‘--null-data’) option, and ‘grep -P’ may warn of
unimplemented features. Other Options.
In addition, two variant programs ‘egrep’ and ‘fgrep’ are available.
‘egrep’ is the same as ‘grep -E’. ‘fgrep’ is the same as ‘grep -F’.
Direct invocation as either ‘egrep’ or ‘fgrep’ is deprecated, but is
provided to allow historical applications that rely on them to run
unmodified.