YA: Simple Contact Form Processing

<?php
/*
    Answer Script For Yahoo Question:
    http://answers.yahoo.com/question/index?qid=20110924135432AAWKmca
*/

$fileName = 'file.txt'; // The name of the file, as to where the data will be saved.
$template = '
<div style="border: 1px dotted #999;padding: 8px;">
    <p><span style="font-style: italic;">Name</span>: <span style="font-weight: bold">{NAME}</span></p>
    <p><span style="font-style: italic;">Email</span>: <span style="font-weight: bold">{EMAIL}</span></p>
    <p><span style="font-style: italic;">Message</span>:<br /> <span style="font-weight: bold">{MESSAGE}</span></p>
</div>
'; // Template of how you want the message to be displayed.
$showForm = true; // Whether or not to show the form

if(isset($_POST['submit'])){ // The Form Has been Submitted
    $name = $_POST['vardas'];
    $email = $_POST['mail'];
    $message = $_POST['tekstas'];
    if(strlen($name) === 0 || strlen($email) === 0 || strlen($message) === 0){
        echo 'All fields are required.<br />';
    }else{
        $templateFills = Array(
        '{NAME}' => $name,
        '{EMAIL}' => $email,
        '{MESSAGE}' => $message
        );
        $string = file_get_contents($fileName) or '';
        $string .= str_replace( array_keys($templateFills), array_values($templateFills), $template);
        file_put_contents($fileName, $string);
        echo $string;
        $showForm = false;
    }
}

if($showForm){
echo '
<form action="" method="post" name="forma">
    <p>
        Vardas<br />
        <input type="text" name="vardas" value="' . $_POST['vardas'] . '" />
    </p>
    <p>
        E-mail<br />
        <input type="text" name="mail" value="' . $_POST['mail'] . '" />
    </p>
    <p>
        Tekstas<br />
        <textarea cols="30" rows="8" name="tekstas">' . $_POST['tekstas'] . '</textarea>
    </p>
    <br/>
    <input value="Spausk" type="submit" name="submit" />
</form>
';
}
?>