Compare file1 with file2. Use standard input if file1 is - or missing. This command is normally used for comparing binary files, although files can be of any type. (See also comm and diff.) skip1 and skip2 are optional offsets in the files at which the comparison is to start.
Print differing bytes as characters.
Ignore the first num bytes of input.
Print offsets and codes of all differing bytes.
Work silently; print nothing, but return exit codes:
Files are identical.
Files are different.
Files are inaccessible.
Print a message if two files are the same (exit code is 0):
cmp -s old new && echo 'no changes'