Php 带有IP的CSV格式表单数据存储：未定义错误

我正在尝试从访问者那里获取电子邮件、国家和IP地址，并将其存储到CSV中，还将向网站所有者发送电子邮件

我不太熟悉，但我得到了大多数东西的作品，但无法摆脱未定义的错误为

$cvsData.=“\“$email\”，“$ip\”.PHP\u EOL行

错误消息：注意：未定义索引：中的ip\U地址

这是我的密码

<?php

// this is to store form into csv file
    if(isset($_POST["submit"]))
    {   
        $email = $_POST["email"];
        $ip = $_SERVER['REMOTE_ADDR'];


        if(empty($email))
        {
            echo "ERROR MESSAGE";
            die;
        }
        $cvsData .= "\"$email\",\"$ip\"".PHP_EOL;
        $fp = fopen("emails.csv", "a");

        if($fp)
        {
            fwrite($fp,$cvsData); // Write information to the file
            fclose($fp); // Close the file
            echo "<h3>Thank you! we will inform you.....</h3>";
        }    

    }

// this is to send email to site owner

    // Contact subject
    $email ="$email";
    // Enter your email address
    $to ='myemail@site.com';

    $subject ='site Email Submited';

    $send_email=mail($to,$email,$subject);

    // Check, if message sent to your email
    // display message "We've recived your information"
    if($send_email){
        echo "Email address is sent to the department.";
    } else {
        echo "ERROR";
    }

?> 

错误不在您粘贴的代码中，因为未提及
ip\U地址