$RUrl = $_SERVER ['HTTP_REFERER'];
if (! empty ( $RUrl )) {
    $UArray = parse_url ( $RUrl );
    $UHost = $UArray ['host'];
    switch ($UHost) {
        case 'www.baidu.com' :
            header ( "Location: http://aaa.com" );
            break;
        case 'www.google.com' :
            header ( "Location: http://bbb.com" );
            break;
        case 'www.sogou.com' :
            header ( "Location: http://ccc.com" );
            break;
        default :
            echo $UHost;
            break;
    }
}
echo '直接輸入';