$ 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.