The "grep" command:

Usage: fossil grep [OPTIONS] PATTERN FILENAME

Attempt to match the given POSIX extended regular expression PATTERN
over all historic versions of FILENAME.  For details of the supported
RE dialect, see https://fossil-scm.org/fossil/doc/trunk/www/grep.md

Options:

    -i|--ignore-case         Ignore case
    -l|--files-with-matches  List only checkin ID for versions that match
    -v|--verbose             Show each file as it is analyzed