From the NannyMUD documentation

LAST CHANGE

2000-12-14

FUNCTION

NAME
        file_name - Find the filename of an object.


SYNTAX
	string file_name(object ob)

DESCRIPTION
	This function gives the filename of an object concatenated
	with a possible instance number. This typically is a string
	on the form "std/weapon#423". Instance numbers are unique for
	all objects in the game.

	If a filename has no instance number it is the 'master object'
	and not a 'cloned copy'.