php获取域名正则表达式

$s = 'aaa.baidu.com www.baidu.com www.baidu.com.cn www.baidu.info';
preg_match_all('/(\w+)\.(?:com|info)/i', $s, $r);
print_r($r);

Array
(
    [0] => Array
        (
            [0] => baidu.com
            [1] => baidu.com
            [2] => baidu.com
            [3] => baidu.info
        )

    [1] => Array
        (
            [0] => baidu
            [1] => baidu
            [2] => baidu
            [3] => baidu
        )

)