#!/usr/bin/perl -w
# http://www.cyut.edu.tw/~ckhung/b/pl/
use strict;
use Tk;
my ($main, $e, $b);

$main = MainWindow->new(-title=>"Demo");
$e = $main->Entry();
$b = $main->Button(-command=>\&update);
$e->pack(-expand=>"yes", -fill=>"both");
$b->pack(-expand=>"yes", -fill=>"both");
MainLoop();

sub update {
    my ($t) = $e->get();
    $b->configure(-text=>$t);
}