Someone

<?php

$filename = 'test.txt';
$file = ''; 
if(file_exists($filename)) {
    if(isset($_POST['submit'])) {
        $file = $_POST['editor'];
        file_put_contents($filename, $file);
        echo '<p>Saved</p>';
    } else {
        $file = file_get_contents($filename);
    }   
    $file = htmlspecialchars($file);
}
?>

<form method="POST" action="">
<textarea name="editor" cols="40" rows="10"><?php echo $file ?></textarea>
<br />
<input type="submit" name="submit" value="Save" />
</form>