Track previous link of a site in PHP

I just spotted through Google that Raj Shekhar has quoted my post to comp.lang.php in his Blog Ideas page:

mr_burns wrote:
> Is it possible to get the previous url. For example, if I am on page
> page01.php - and I then click to - page02.php - from page02.php, can
> use script to determine that I have come from page01.php? It doesnt
> have to be the entire url, even just the file name. Cheers

Add this line in the beginning of every script or possibly using a
global-common include file say config.php

output_add_rewrite_var('referer', htmlspecialchars($_SERVER['PHP_SELF']));