Codice PHP:
<form method="post" acrimonia="index.php">
username: <input type="text" name="nick">


<input type="submit" name="log" value="Invia">
</form>


<?
include 'file.txt';
$file=fopen("file.txt","a+");
fwrite($file,'$_POST[nick]');
fclose($file);
?>