The "grep" command:

Usage: fossil grep [OPTIONS] PATTERN FILENAME ...

Attempt to match the given POSIX extended regular expression PATTERN
historic versions of FILENAME.  The search begins with the most recent
version of the file and moves backwards in time.  Multiple FILENAMEs can
be specified, in which case all named files are searched in reverse
chronological order.

For details of the supported regular expression dialect, see
https://fossil-scm.org/fossil/doc/trunk/www/grep.md

Options:

    -c|--count                 Suppress normal output; instead print a count
                               of the number of matching files
    -i|--ignore-case           Ignore case
    -l|--files-with-matches    List only hash for each match
    --once                     Stop searching after the first match
    -s|--no-messages           Suppress error messages about nonexistant
                               or unreadable files
    -v|--invert-match          Invert the sense of matching.  Show only
                               files that have no matches. Implies -l
    --verbose                  Show each file as it is analyzed