PHP getenv() 获取IP

<?php
function GetIP(){
if (getenv("HTTP_CLIENT_IP")
&& strcasecmp(getenv("HTTP_CLIENT_IP"), "unknown"))
$ip = getenv("HTTP_CLIENT_IP");
else if (getenv("HTTP_X_FORWARDED_FOR")
&& strcasecmp(getenv("HTTP_X_FORWARDED_FOR"), "unknown"))
$ip = getenv("HTTP_X_FORWARDED_FOR");
else if (getenv("REMOTE_ADDR")
&& strcasecmp(getenv("REMOTE_ADDR"), "unknown"))
$ip = getenv("REMOTE_ADDR");
else if (isset($_SERVER['REMOTE_ADDR'])
&& $_SERVER['REMOTE_ADDR']
&& strcasecmp($_SERVER['REMOTE_ADDR'], "unknown"))
$ip = $_SERVER['REMOTE_ADDR'];
else
$ip = "unknown";
return($ip);
}
$ip = GetIP();
echo $ip;
?>