zdiff --version (return code: 0)
zdiff (gzip) 1.6
Copyright (C) 2009, 2011-2013 Free Software Foundation, Inc.
This is free software. You may redistribute copies of it under the terms of
the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
There is NO WARRANTY, to the extent permitted by law.
Written by Jean-loup Gailly.
zdiff --help (return code: 0)
Usage: /bin/zdiff [OPTION]... FILE1 [FILE2]
Compare FILE1 to FILE2, using their uncompressed contents if they are
compressed. If FILE2 is omitted, compare FILE1 to the uncompressed
contents of FILE1.gz. Do comparisons like 'diff' does.
OPTIONs are the same as for 'diff'.
Report bugs to <bug-gzip@gnu.org>.