[bug-grep] -X option undocumented (in --help, doc/grep.1, doc/grep.texi)

[Charles Levert]

The current discussion about using "egrep" and "fgrep" instead of
"grep -E" and "grep -F" reminded me of a simple fact that I noticed.

The '-X' option, and in particular its use with the "awk" matcher
("-X awk") is undocumented.

In the "--help" text, a line such as

  "  -X MATCHER                PATTERN is a MATCHER regular expression"

could be added right after the '-P' one.

The '-X' option also goes undocumented in "doc/grep.1" and
"doc/grep.texi".