$ip = $_SERVER["REMOTE_ADDR"];
        
        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";
getenv函数，从环境中取字符串,获取环境变量的值

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