PHP: How to get referrer URL?

$_SERVER['HTTP_REFERER'] will give you the referrer page's URL if there exists any. If users use a bookmark or directly visit your site by manually typing in the URL, http_referer will be empty. Also if the users are posting to your page programatically (CURL) then they're not obliged to set the http_referer as well. You're missing all _, is that a typo?

If $_SERVER['HTTP_REFERER'] variable doesn't seems to work, then you can either use Google Analytics or AddThis Analytics.

Underscore. Not space.

$_SERVER['HTTP_REFERER']