use Tk;
my $mw = MainWindow->new();
my $var;
my @list = qw(jan feb mar apr);
my $opt = $mw->Optionmenu(
            -options => [@list],
            -command => sub { print "got: ", shift, "\n" },
            -variable => \$var,
            )->pack;
$opt->addOptions([may=>5],[jun=>6],[jul=>7],[aug=>8]);
$mw->Label(-textvariable=>\$var, -relief=>'groove')->pack;
$mw->Button(-text=>'Exit', -command=>sub{$mw->destroy})->pack;

$mw->Button(
    -text => 'Select Random',
    -command => sub {
        $opt->setOption( $list[int rand @list] );
    }
)->pack;

MainLoop;