if ($optimize_history) {
    # remove duplicities from history
    my @history = $term->GetHistory($file);
    my %history = map {$_ => 1} @history;
    my @new_history = ();

    for (reverse @history) {                    # in reverse order
      if ($history{"$_"}) {                     # if not remembered yet
        unshift @new_history, $_;               #   remember history line
        delete $history{"$_"};                  #   and remove it
      }
    }

    $term->SetHistory(@new_history);            # set history to new list
    $term->WriteHistory($file);                 # save history
  } else {
    # only add new line to the history file
    $term->WriteHistory($file);
  }