if ($key eq 'groups') {
   if ($param->{$key} =~ m/[^0-9\,\-\|]/) { # check for illegal characters in group-definition
      print "\n>>> Illegal characters in groups-definition '".$param->{$key}."'! Only 0-9 and , and - and | are allowed!\n";
      $error = 1;
   }
   last CASE;
}
if ($key eq 'gh') {
   if ($param->{$key} =~ m/[^0-9]/) {
      print "\n>>> Illegal characters in graph-height '".$param->{$key}."'! Only 0-9 are allowed!\n";
      $error = 1;
   }
   last CASE;
}