2.4 grep Programs

grep searches the named input files (or standard input if no files are named, or the file name ‘-’ is given) for lines containing a match to the given pattern. By default, grep prints the matching lines. 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, separated by newlines, any of which is to be matched. (‘-F’ is specified by POSIX.)

‘-P’

‘--perl-regexp’

Interpret the pattern as a Perl regular expression. This is highly experimental and ‘grep -P’ may warn of unimplemented features.

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.

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