$ mkdir -p dir1/a/b/c
$ mkdir -p dir2/a/b
$ echo 1a1 > dir1/a/1
$ echo 2a1 > dir2/a/1
$ touch dir1/a/2
$ touch dir2/a/2
$ touch dir1/a/b/x
$ diff -rq dir1 dir2
Files dir1/a/1 and dir2/a/1 differ
Only in dir1/a/b: c
Only in dir1/a/b: x