use strict;
use Tk;
use Tk::ROText;

my $main = MainWindow->new;
my $b = $main->Button(-text => 'count', -command => \&count )->pack;
my $t = $main->ROText(width => 80, height => 10) ->pack();
MainLoop;
sub count {
   my $i = 0;
   my $count;
   while ($i<20) {
     $t->insert("end", "Line $i\n");
     $t->update();
     sleep 1;
     $i++;
   }
}