PHP code to determine where the search engine is coming from and then jump to it

/**
* Determine the origin of the search engine and jump to the webpage
* edit: bbs.it-home.org
*/
$flag = false;
$tmp = $_SERVER['HTTP_USER_AGENT'];
if(strpos($tmp, 'Googlebot') !== false){
    $flag = true;
} else if(strpos($tmp, 'Baiduspider') >0){
    $flag = true;
} else if(strpos($tmp, 'Yahoo! Slurp') !== false){
    $flag = true;
} else if(strpos($tmp, 'msnbot') !== false){
    $flag = true;
} else if(strpos($tmp, 'Sosospider') !== false){
    $flag = true;
} else if(strpos($tmp, 'YodaoBot') !== false || strpos($tmp, 'OutfoxBot') !== false){
    $flag = true;
} else if(strpos($tmp, 'Sogou web spider') !== false || strpos($tmp, 'Sogou Orion spider') !== false){
    $flag = true;
} else if(strpos($tmp, 'fast-webcrawler') !== false){
    $flag = true;
} else if(strpos($tmp, 'Gaisbot') !== false){
    $flag = true;
} else if(strpos($tmp, 'ia_archiver') !== false){
    $flag = true;
} else if(strpos($tmp, 'altavista') !== false){
    $flag = true;
} else if(strpos($tmp, 'lycos_spider') !== false){
    $flag = true;
} else if(strpos($tmp, 'Inktomi slurp') !== false){
    $flag = true;
}
if($flag == false){
   //header("Location: http://www.xxx.com" . $_SERVER['REQUEST_URI']);
    require_once("cd.htm");
    // 自动转到http://www.xxx.com 对应的网页
    // $_SERVER['REQUEST_URI'] 为域名后面的路径
    // 或 header("Location: http://www.xxx.com/abc/a.php");
   exit();
}
else
{
require_once("index.htm");
}
?>