$siebdb = 'somekey';

$preprod->{$siebdb} = "DISK:\\db2_backup\\";
$prod->{$siebdb} = "USEREXIT";

if($preprod->{$siebdb} ne $prod->{$siebdb}) {
   print "NOT EQUAL";
} else {
   print "EQUAL";
}
[download]

outputs

NOT EQUAL
[download]

You should be getting the same.