Using PHP, how do I determine which page I came from? -

first off, php noob. said, have php code given me creates paypal shopping cart. 1 of buttons (continue shopping) on cart page supposed return previous product page (of there several such pages) has view cart button.

how determine product page return to? put page name (i.e. "productlist1.html") in hidden field?

regarding possible duplicate: saw page, , comment on page "the problem http_referer unreliable @ best.", decided ask again since asked in 2009, , maybe things have changed since then.

in php:

/* print page came */ print $_server['http_referer']; 

but if come own page, can modify link adding parameter such ?product_id=123 @ end of link , in php:

/* print product id */ print $_get['product_id'];