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. This is the default.

`-E'

`--extended-regexp'

Interpret the pattern as an extended regular expression.

`-F'

`--fixed-strings'

Interpret the pattern as a list of fixed strings, separated by newlines, any of which is to be matched.

`-P'

`--perl-regexp'

Interpret the pattern as a Perl regular expression.

In addition, two variant programs EGREP and FGREP are available. EGREP is the same as `grep -E'. FGREP is the same as `grep -F'.