Gentoo Development Guide

grep -- Text Filtering

The grep tool can be used to extract lines matching a given regular expression from a file, or to check whether a given regular expression matches any line in a file.

The usage is grep "pattern" files. If no files are specified, text is read from the standard input. The pattern is a standard basic regular expression, as described in IEEE1003.1-2004-9.3.

If the -E argument is supplied, pattern is treated as being an extended regular expression as described in IEEE1003.1-2004-9.4.

If the -F argument is supplied, pattern is treated as being a fixed string rather than a regular expression.

By default, grep prints out matching lines from the input. If -q is specified, no output is displayed. If -l (lowercase letter ell) is specified, only the filenames of files which contain matching lines are displayed.

The -v option can be used to select lines which do not match the pattern instead.

The -s option can be used to suppress messages about nonexistent or unreadable files.

The return code can be used to test whether or not a match occurred. A return code of 0 indicates that one or more matches occurred; a code of 1 indicates no matches.

See IEEE1003.1-2004-grep for details. The grep-1 manual page on GNU systems documents many non-portable additional features.