A couple of weeks back I had to write a solution for a client to track the referrer search engine from where the user came to his sites contact page, without using Google Analytics. If a user was to fill the contact form on the website, the referring search engine name and the keyword for which it was refereed was to be emailed along with the contact information. The following is a solution for the same.

The code itself is pretty simple - it checks the $_SERVER['HTTP_REFERER'] and, based on an array of search engine types, looks for a certain "query" keyname in the URL and matches what follows (with a regular expression). This can be useful for not only determining what sort of audience is visiting your site, but could also be used to present a custom message to visitors from certain search engines (or, more complicated, to show different content based on search terms).

This tutorial looks at the process of reciprocal links. That is, links generated from websites that have links to your own page. These links back to a page can be detected from the HTTP REFERER which, in PHP, can be detected via the super global variable $_SERVER['HTTP_REFERER']. Care should be taken when using this variable as it is set from userland and, as such, should not be trusted.

His method stores the linking information (gathered from the referrer) and calls an addLinks method that checks to ensure the page format is valid and that it's a real site before putting it into the table. Complete code for this, a fetch method and a simple database layer to put it on top of are included.

caching services such as coral content distribution network provide an alternative for when your site goes down, but why wait until it gets to that stage? why not just send all your hits from high-end websites to the coral cache version? well, there isn't a good reason not to, so i'll show you how to do it automatically.

He provides the simple script that looks for certain sites in the "HTTP_REFERER" value of incoming calls and pushes them off to the cached location with a header() redirect. The whole thing is only 12 lines, not counting the $sites array.