use Tk;
use Tk::ProgressBar;
my $mw = MainWindow->new();
my $per = 0;
$mw->ProgressBar(-variable=>\$per)->pack;
$mw->Button(-text=>"Go",-command=>\&GoForIt)->pack;
MainLoop;

######### This is the important bit ###########
sub GoForIt {
    $mw->repeat(25=>sub{$per+=10;return if $per>100;;$mw->update;sleep(1)})
}