sub nickchange {
    my $window2 = $fenster->Toplevel;
    my $text = $window2->Label(-text => "Nickname eingeben")->pack();
    my $entry = $window2->Entry()->pack();
    my $button = $window2->Button(-text => 'Ok',-command => \&action)->pack();
    sub action {
        my $eingabe = $entry->get();
        $window2->destroy();
        $variable = $eingabe;
    }
}