捕获名称，电子邮件并保存到.csv文件 - PHP

Question

我有一个html表单（方法POST，链接到以下PHP脚本等），但无法看到我的脚本无法正常工作的原因。

应该从表单（mname，memail）中获取名称和电子邮件，验证它们，然后将值保存到“mailinglist.csv”中。我不能让它工作。

这是我的剧本：

    <?php

//variables set to empty
$mnameErr = $memailErr = "";
$mname = $memail = "";


    //validate name
    if ($_SERVER["REQUEST_METHOD"] == "POST") {
        if(empty($_POST["mname"])) {
            $mnameErr = "Name is required";
        } else {
            $mname = test_input($_POST["mname"]);
            //checks if name only contains letters and whitespaces
            if (!preg_match("/^[a-zA-Z ]*$/",$mname)) {
                $mnameErr = "Only letters and white space allowed";
            }
        }

    //validate email
    if (empty($_POST["memail"])) {
        $memailErr = "Email is required";
    } else {
        $memail = test_input($_POST["memail"]);
        //checks if email address is well-formed
        if (!filter_var($memail, FILTER_VALIDATE_EMAIL)) {
            $memailErr = "Invalid email format";
        }
    }

    //validate data function
    function test_input($data) {
        $data = trim($data);
        $data = stripslashes($data);
        $data = htmlspecialchars($data);
        return $data;

    //saves details to mailinglist.csv
    if($memailErr != "") 
    {
        echo("There was an error.");
    } else {
        $fs = fopen("mailinglist.csv","a");
        $txt = $mname.", ".$memail."\n";
        fwrite($txt);
        fclose($fs);

        header("Location: thankyou.html");
    }

    exit;
    }
}
?>