Ah Yes, I had this problem before, here's a quick-and-dirty progress bar script that uses and example

#progress bar that monitors a compile,
#by counting .o's periodically
use Tk;
sub tick;
$total_objects = 303;
$progressbar_width = 2*$total_objects;
$progressbar_height = 50;
$timer_interval=10; #in seconds
$MW = MainWindow->new;
$MW->bind('<Control-c>' => \&exit);
$MW->bind('<Control-q>' => \&exit);
$canvas1 = $MW->Canvas(
  '-width' => $progressbar_width,
  -height => $progressbar_height,
  -background => 'black'
) -> pack;
$newval = 10;
$start = $MW->Button(
    -text         => 'Start', 
    -command      => sub {tick},
);
$start->pack(-side => 'left', -fill => 'both', -expand => 'yes');

sub tick {
    # Update the counter every 5 seconds
    $MW->after($timer_interval * 1000, \&tick);
    $num_objs = @objects = glob("\\as900\\code\\build\\*.o");
    print "\n$num_objs out of $total_objects built so far...";
    $newval = ($num_objs / $total_objects)*$progressbar_width;
    $canvas1->create ('rectangle','0','0',$newval,$progressbar_height,
+-fill=>'red');
} 
MainLoop;
[download]

This gives you the capability of a timer callback.
Desert coder