Finding the location of an included script

Is this possible? I'm trying to write a back end to be used in most of my websites. While I can simply use symlinks to ensure this is included from my various sites but only exists once on the hardrive, I'd prefer to simply include the file and have the script itself work out where it lives. So if I have: include("/path/to/backend.php"); Is there a way from inside of backend.php to return "/path/to" ? Gadi