diff -r directory1 directory2
If you want "no difference found", then write a script. In that script, send the output to a scratch file. Then test whether the file contains any bytes (use the -s conditional expression in bash), and if it doesn't, then echo no difference found. For further details on the -s conditional expression, see the man page:
Don't confuse it with the -s switch! In the man page, search for
and then search for -s.
For help with conditional expressions and general help on writing bash scripts, see
Hope this helps.