Hmm, the example page doesn't convince me, for example

> The diff utility can compare files and print their differences. If we pass it the result of ls commands, we can compare the contents of directories.

No, if you pass the output of ls commands, you might get an error because you'll pass a bunch of files to diff.

And last but not least there's

    diff -r directory-a directory-b

to compare two directories file by file.