Whois with PHP

<html>

 <?php
        $domain = $_GET["dominio"];
        $protect = explode(" ", $domain);
        if(in_array("&&", $protect) || in_array("rm", $protect)){
                echo "erro!";
        }else{
                $cmd = "whois ".$domain;
                $whois = shell_exec ($cmd);
        }
 ?>
 <pre>
        <?php echo $whois; ?>
 </pre>


</html>