Comparing directory structures

I would like to compare 2 directory structions & get a list of the files that are different from eachother.

For ex. if /dir1/sub/file.php is different from /dir2/sub/file.php, I want this command to output "sub/file.php" . Then I will run a script to get the actual differences in the files that are outputted.

What is the quickest way to do this?

I tried looping through the files in one structure and comparing them with the same files in the other structure. But I'm stuck because I can't figure out how to get the filename out of a full path.
Basically, how can I get "file.php" from the string "/dir1/sub/file.php" ?

You could do something like this:
ls -1 /path/to/dir1 | sort > /path/to/dirlist1.txt
ls -1 /path/to/dir2 | sort > /path/to/dirlist2.txt
diff /path/to/dirlist1.txt /path/to/dirlist2.txt | less

it is not very clear what you want, what Scorpions4ever said it's to compare just the filenames, not content..
you need for content? and can those sub/ have other sub-directories?