cmp

cmp [options] file1 file2 [skip1 [skip2] ]

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 diff.) skip1 and skip2 are optional offsets in the files at which the comparison is to start.

Options
-c, --print-chars	Print differing bytes as characters.
-i num, --ignore-initial=num	Ignore the first num bytes of input.
-l, --verbose	Print offsets and codes of all differing bytes.
-s, --quiet, --silent	Work silently; print nothing, but return exit codes: 0 : Files are identical. 1 : Files are different. 2 : Files are inaccessible.

Example
Print a message if two files are the same (exit code is 0):
cmp -s old new && echo 'no changes'