php正则表达式匹配URL中的域名

$search = '~^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?~i';
$url = 'http://www.php.net/pub/ietf/uri/#Related';
$url = trim($url);
preg_match_all($search, $url ,$rr);
printf("输出URL数据为：
%s\n",var_export( $rr ,TRUE));
/*
各分组如下
      $1 = http:
      $2 = http
      $3 = //www.php.net
      $4 = www.php.net
      $5 = /pub/ietf/uri/
      $6 =
      $7 =
      $8 = #Related
      $9 = Related
*/
?>

这里提供另一个简洁的代码：

// 从 URL 中取得主机名
preg_match("/^(http:\/\/)?([^\/]+)/i", "http：//www.php.net/index.html", $matches);
$host = $matches[2];
// 从主机名中取得后面两段
preg_match("/[^\.\/]+\.[^\.\/]+$/", $host, $matches);
echo "domain name is: {$matches[0]}\n";
?>

执行后输出：domain name is: php.net