Description of problem:

The synonymous -F and --fixed-strings command-line options are used to interpret the pattern as a list of fixed strings, separated by newlines, any of which is to be matched. This is correctly mentioned both on the man page and in the usage message. Apart from these, however, the option --fixed-regexp appears to serve quite the same purpose, despite it not being documented anywhere.

$ echo 'studying' | grep -F 'dying'
studying
$ echo 'studying' | grep --fixed-strings 'dying'
studying
$ echo 'studying' | grep --fixed-regexp 'dying'
studying

Inasmuch as I could tell, this was probably the only undocumented option synonymous to -F. It does not work with an arbitrary string starting with the "--fixed-" prefix:

$ echo 'studying' | grep --fixed-fence 'dying'
grep: unrecognized option '--fixed-fence'
Usage: grep [OPTION]... PATTERN [FILE]...
Try 'grep --help' for more information.

To fix this bug, the --fixed-regexp command-line option should be either included in the documentation or wholly removed.


Version-Release number of selected component (if applicable):
grep-2.16-1.el7.x86_64


How reproducible:
always