I would like to know how to create a php function that can be installed in php just like the already built in functions like :

rename copy

The main point I would like to achieve is a simple php function that can be called from ANY php page on the whole host without needing to have a php function within the php page / needing an include.

so simply I would like to create a function that will work like this :

location();

That without a given input string will output the current location of the file via echo etc