Which file am I ?

Hello ! I need to know wether a file "test.php" has been included in some other file or is called directly. Therefor, I want to compare the PATH_INFO and the filename "test.php". This works fine. Now I have a lot of files like "test.php" all with different names. How can I get the filename without saying $this_file = "..." ? I found nothing in phpinfo(). When the file is included, only the name of the file, which includes my file, is shown. Regards Martin