Function for Extract Search String From Search URL ( Different Search Engine )in PHP

function search_engine_query_string($url = false) {

if(!$url) {
$url = isset($_SERVER['HTTP_REFERER']) ? $_SERVER['HTTP_REFERER'] : false;
}
if($url == false) {
return '';
}

$parts = parse_url($url);
parse_str($parts['query'], $query);

$search_engines = array(
'bing' => 'q',
'google' => 'q',
'yahoo' => 'p'
);

preg_match('/(' . implode('|', array_keys($search_engines)) . ')\./', $parts['host'], $matches);

return isset($matches[1]) && isset($query[$search_engines[$matches[1]]]) ? $query[$search_engines[$matches[1]]] : '';

}