What variables do search engines pass

I am trying to figure out if my site traffic is from a search engine or a referrer. What parameters do search engines pass? This is untest code to give you guys an idea of what I am trying to do.

$se_array = array(google.com, msn.com, yahoo.com, bing.com, altavista.com);
foreach ($se_array as $se_name) {
    $se_found = preg_grep($se_name, $_REQUEST);
    if($se_found){
        //Do what I want to do to search engine traffic
    }
} else {
    // Do what I want to do with referrer traffic
}

PHP:

 

$_SERVER['HTTP_USER_AGENT'];

PHP:

You'll have to research this one. Google calls itself Googlebot, Yahoo! is Slurp, etc. They all come up with creative names to impress themselves.

Here is a quick snippet to get you on your way:
http://stackoverflow.com/questions/1154420/how-to-detect-search-engine-visites-on-my-site-like-phpbb

 

I don't care about bots. Does google initilize the HTTP_USER_AGENT variable when sending, search engine traffic to a site?

 

Why dont you use google analytics ?
It will give all the details as you need and also more than what you expect.

 

What? Isn't that what you asked for, when a search engine is visiting your site? Please be more specific.

 

I do use Google Analytics for tracking my website statistics. The data I am trying to get cam be used for more than statistics tracking I am going to use this data for more than that too. I really mean this, thanks for the info.

If it was, then you need to listen to what I am thinking and not to what I said. I am trying to find out if my traffic was sent from a search engine (organic traffic) or one of my referrers(referral traffic). I will show different pages to organic traffic than I show to referral traffic. I certainly could have worded my question better, than I did in the OP.

Does Google, Yahoo, MSN, Bing and the other top rated search engines label it's organic traffic so I can distinguish between the organic and referral traffic.