PHP正则表达式从url中取得域名

以下代码可以从URL中获得域名

例如:http://bkjia.com/live/q.html

得到bkjia.com

以下为引用的内容：
function get_domain($url){
$pattern = "/[\w-]+\.(com|net|org|gov|cc|biz|info|cn)(\.(cn|hk))*/";
preg_match($pattern, $url, $matches);
if(count($matches) > 0) {
return $matches[0];
}else{
$rs = parse_url($url);
$main_url = $rs["host"];
if(!strcmp(long2ip(sprintf("%u",ip2long($main_url))),$main_url)) {
return $main_url;
}else{
$arr = explode(".",$main_url);
$count=count($arr);
$endArr = array("com","net","org","3322");//com.cn net.cn 等情况
if (in_array($arr[$count-2],$endArr)){
$domain = $arr[$count-3].".".$arr[$count-2].".".$arr[$count-1];
}else{
$domain = $arr[$count-2].".".$arr[$count-1];
}
return $domain;
}// end if(!strcmp...)
}// end if(count...)
}// end function