PHP获取客户端的真实IP

global $ip;
if (getenv("HTTP_CLIENT_IP")){
    $ip = getenv("HTTP_CLIENT_IP");
}else if(getenv("HTTP_X_FORWARDED_FOR")){
    $ip = getenv("HTTP_X_FORWARDED_FOR");
}else if(getenv("REMOTE_ADDR")){
    $ip = getenv("REMOTE_ADDR");
}else{
    $ip = "Unknow";
}
echo $ip;