how to logging google search keywords

$thereferer = strtolower($_SERVER['HTTP_REFERER']);
$a = substr($thereferer, strpos($thereferer, "q="));
$a = substr($a, 2);
if (strpos($a, "&")) {
$a = substr($a, 0, strpos($a, "&"));
}
$googlekeywords = urldecode($a);
return $googlekeywords;

Google+ syck