$cache_file = dirname(__FILE__).'/cache/'.md5($search_string).'.txt';
if( file_exists($cache_file) && (filemtime($cache_file) + 900) > time() ){
echo file_get_contents($cache_file);
}else{
//arama vs islemleri sonucun $result degiskeninde oldugunu varsaydim.
file_put_contents($cache_file, $result);
echo $result;
}