rcsdiff --version (return code: 0)
rcsdiff (GNU RCS) 5.9.4 Copyright (C) 2010-2015 Thien-Thi Nguyen Copyright (C) 1990-1995 Paul Eggert Copyright (C) 1982,1988,1989 Walter F. Tichy, Purdue CS License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.
rcsdiff --help (return code: 0)
Usage: rcsdiff [options] file ... Compare RCS revisions. Options: -rREV (zero, one, or two times) Name a revision. -kSUBST Substitute using mode SUBST (see co(1)). -q Quiet mode. -T No effect; included for compatibility with other commands. -V Obsolete; do not use. -VN Emulate RCS version N. -xSUFF Specify SUFF as a slash-separated list of suffixes used to identify RCS file names. -zZONE Specify date output format in keyword-substitution. If given two revisions (-rREV1 -rREV2), compare those revisions. If given only one revision (-rREV), compare the working file with it. If given no revisions, compare the working file with the latest revision on the default branch. Additionally, the following options (and their argument, if any) are passed to the underlying diff(1) command: -0, -1, -2, -3, -4, -5, -6, -7, -8, -9, -B, -C, -D, -F, -H, -I, -L, -U, -W, -a, -b, -c, -d, -e, -f, -h, -i, -n, -p, -t, -u, -w, -y, [long options (that start with "--")]. (Not all of these options are meaningful.) Report bugs to: <email@example.com> RCS home page: <http://www.gnu.org/software/rcs/> General help using GNU software: <http://www.gnu.org/gethelp/>