PHP: Как записать данных из формы в текстовый файл

<form action method="post">
 <input name="field1" type="text" />
 <input name="field2" type="text" />
 <input type="submit" name="submit" value="Save Data">
</form>

<?php
if(isset($_POST['field1']) && isset($_POST['field2'])) {
 $data = $_POST['field1'] . '-' . $_POST['field2'] . "\r\n";
 $ret = file_put_contents('/tmp/mydata.txt', $data, FILE_APPEND | LOCK_EX);
 if($ret === false) {
 die('There was an error writing this file');
 }
 else {
 echo "$ret bytes written to file";
 }
}
else {
 die('no post data to process');
}
?>