gdiffmk --version (return code: 0)
GNU gdiffmk (groff) version 1.22.3
gdiffmk --help (return code: 255)
Usage: gdiffmk [ OPTIONS ] FILE1 FILE2 [ OUTPUT ] Place difference marks into the new version of a groff/nroff/troff document. FILE1 and FILE2 are compared, using `diff', and FILE2 is output with groff `.mc' requests added to indicate how it is different from FILE1. FILE1 Previous version of the groff file. `-' means standard input. FILE2 Current version of the groff file. `-' means standard input. Either FILE1 or FILE2 can be standard input, but not both. OUTPUT Copy of FILE2 with `.mc' commands added. `-' means standard output (the default). OPTIONS: -a ADDMARK Mark for added groff source lines. Default: `+'. -c CHANGEMARK Mark for changed groff source lines. Default: `|'. -d DELETEMARK Mark for deleted groff source lines. Default: `*'. -D Show the deleted portions from changed and deleted text. Default delimiting marks: `[[' .... `]]'. -B By default, the deleted texts marked by the `-D' option end with an added troff `.br' command. This option prevents the added `.br'. -M MARK1 MARK2 Change the delimiting marks for the `-D' option. -x DIFFCMD Use a different diff(1) command; one that accepts the `-Dname' option, such as GNU diff. --version Print version information on the standard output and exit. --help Print this message on the standard error.