Zcmp and zdiff are used to invoke the cmp or the
diff program on files compressed via gzip. All options specified
are passed directly to cmp or diff. If only file1 is
specified, it is compared to the uncompressed contents of file1.gz. If
two files are specified, their contents (uncompressed if necessary) are fed to
cmp or diff. The input files are not modified. The exit status
from cmp or diff is preserved.