my $dlg = Tk::DialogBox->new(-title => 'Login', -buttons => ['Ok', 'Cancel']);  # this line doesn't work
$dlg->add('Label', -text => 'User name')->pack;
my $user_entry = $dlg->add('Entry')->pack;
$dlg->add('Label', -text => 'Password')->pack;
my $pwd_entry = $dlg->add('Entry', -show => '*')->pack;
my $btn = $dlg->Show;
my $username = $user_entry->get;
my $pwd = $pwd_entry->get;
if ($btn eq 'Ok') {
  print "logging in with user $username and password $pwd\n";
}