PHP判断网站的访问来源是否是蜘蛛

/**
 * 判断是否是蜘蛛
 */
function fromRobot($except = '') {
   $ua = strtolower ( $_SERVER ['HTTP_USER_AGENT'] );
   $botchar = "/(baidu|google|spider|soso|yahoo|sohu-search|yodao|robozilla|AhrefsBot)/i";
   $except ? $botchar = str_replace ( $except . '|', '', $botchar ) : '';
   if (preg_match ( $botchar, $ua )) {
      return true;
   }
   return false;
}