Eu acredito que você pode usar
fgrep -- --help
para conseguir isso. A página man menciona
fgrep -e --help
Cite o link :
-e pattern Specify a pattern used during the search of the input: an input line is selected if it matches any of the specified patterns. This option is most useful when multiple -e options are used to specify multiple patterns, or when a pattern begins with a dash (‘-’).