$ diff -urNa dir1 dir2

-a  Treat  all  files  as text and compare them    
    line-by-line, even if they do not seem to be text.

-N, --new-file
    In  directory  comparison, if a file is found in
    only one directory, treat it as present but empty
    in the other directory.

-r  When comparing directories, recursively compare
    any subdirectories found.
-u  Use the unified output format.