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

Question

For example,

This is index.php

<?
require_once('header.php');
?>

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

--EDIT--

I found a solution:

function backtrace_filename_includes($name){
    $backtrace_array=debug_backtrace();
    if (strpos($backtrace_array[1]['file'],$name)==false){
        return false;
    }else{
        return true;
    }
}

header.php

<?
if (backtrace_filename_includes('index.php')) echo "index.php";
?>

Answer 1

While $_SERVER['PHP_SELF'] will contain the currently executing script, there is no way to determine from an included file which specific script caused the include.

This means that if a.php includes b.php, which includes c.php, c.php will have no way of knowing that b.php was the includer. The best you can get is that a.php is the currently executing script.

---

Edit: Yup, my above answer is technically wrong -- you can use debug_backtrace to find the caller, even without functions, up until PHP 5.4, which removes this functionality.

a.php:

<?php
echo 'A';
include 'b.php';

b.php:

<?php
echo 'B';
include 'c.php';

c.php:

<?php
echo 'C';
print_r(debug_backtrace());

Output:

ABCArray
(
    [0] => Array
        (
            [file] => /tmp/b.php
            [line] => 3
            [function] => include
        )

    [1] => Array
        (
            [file] => /tmp/a.php
            [line] => 3
            [args] => Array
                (
                    [0] => /tmp/b.php
                )

            [function] => include
        )

)

So while this works, you probably shouldn't use it. debug_backtrace can be a noticeable performance drag when used excessively.