#!/usr/bin/perl -w
use strict;
use Tk;
my $mainwindow = MainWindow->new();
my $label = $mainwindow->Label(-text => "This is before you press the button") ->pack();
my $button = $mainwindow->Button(	-text => "press to change the label", 
					-command => sub {
							$label->configure(-text => "This changed the label")
							}
				)->pack();
MainLoop();