Getting name of the main file from external included script..

Hey! I already asked this once before, but nobody seems to answer. That's why I'm re-writing my question.

    I have a main file named: "main.php3"
    It includes an external php3 script named: "ext.php3"

Inside of the 'ext.php3' script - I need to know the full path of the file which included it (in this case - 'http://www......./dir1/dir2/main.php3'). How could I do that? Thank you in advance - Aviv Revach

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