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.