Using a simple example of an exit callback:

#!/usr/bin/perl

use strict;
use warnings;
use Tk;

my $mw = MainWindow->new;
fill_window($mw, 'Main');
my $top1 = $mw->Frame;
fill_window($top1, 'First Frame');

my $tx = $mw->Scrolled('Text', 
    -font => 'normal',
    -width => '73',
    -height => '15',
    -wrap => 'word', 
    -scrollbars => 'e');
$tx->pack;
tie *STDOUT, 'Tk::Text', $tx;

MainLoop;

sub fill_window{
      my ($window, $header) = @_;
      $window->Label(-text => $header)->pack;
      $window->Button(
          '-text' => 'forget',
          '-command' => [$mw => 'destroy']
      )->pack('-side' => 'right'); 
}
[download]