Grabbing referring keyword and making it the sid?

I am sorry if this is already requested somewhere in the past. I looked through a few pages and saw nothing.

I am trying to write some php to satisfy a need i have.

I would like to make links on my page add an sid value based on the referring keyword used to get to the page.

This is what i have gotten so far..

<?php
$ref=@$HTTP_REFERER; 
if (strpos($ref,"google",0) )
{
$keyword = $_GET["q"];
}

elseif (strpos($ref,"yahoo",0) )
{
$keyword = $_GET["p"];
}

elseif (strpos($ref,"msn",0) )
{
$keyword = $_GET["q"];
}

else
{
$keyword = "none";
}

?>

Code (markup):

<a href="http:mydomain.com?sub=rock+<?php echo $keyword; ?>">

Code (markup):

My goal is that the link on the page would add the referring keyword after rock+ and allow me to track the way i want to.

When i put this code on the site and run it i get nothing after the + sign when coming from PPC links and +none when coming from an actual web site i set up a link on to test.

Any help would be greatly appreciated. I have scoured the web and tried alot of examples but nothing seems to be working for me.

 

This might help.

http://forums.digitalpoint.com/showthread.php?t=198486

$_GET cannot be used for referring URLs.