Can an included PHP file know where it was included from?

Question

For example,

This is index.php

Can header.php know it was included by index.php?

Answer 1

Easiest way in the web server environment: $_SERVER['SCRIPT_FILENAME'] will show the original file that is called.

Universal way - debug_backtrace() will show you all previous steps of the execution, which will include calls to require/include functions.