how to create Your Promo Code in php.

$characters = array(
"A","B","C","D","E","F","G","H","J","K","L","M",
"N","P","Q","R","S","T","U","V","W","X","Y","Z",
"1","2","3","4","5","6","7","8","9");
$keys = array();
while(count($keys) < 8) {
    $x = mt_rand(0, count($characters)-1);
    if(!in_array($x, $keys)) {
       $keys[] = $x;
    }
}
foreach($keys as $key){
   $random_chars .= $characters[$key];
}
echo $random_chars;