PHP simple whois script html form

Im just creating a simple tool in PHP what uses the built in whois command in linux and then echo's the response back to the user. Everything I have attempted has either failed or I have messed up somewhere.

<html>
<body>
<form method="POST" action="">
    <input type="text" name="cmd1">
    <input type="submit" value="Submit">
</form>
</body>
</html>
<?php
$cmd = $_POST['cmd1'];
echo "<pre>".shell_exec('whois ', $cmd)."</pre>";
?>

For me nothing happens, for the record I am new to PHP and I would like just a little expertise. Im the only one that is going to be using the script. Thank you.