#! /usr/bin/perl
use warnings;
use strict;

use Tk ();
use Tk::EntryCheck;

my $mw = MainWindow->new();

my $var = 'VAR';
$mw->EntryCheck(-maxlength => 5, -pattern => qr([A-Za-z0-9]),
		-textvariable => \$var)
    ->pack(-side => 'left');
$mw->Button(-text => 'Pushme',
	    -command => sub { $var = '.d'; })
    ->pack(-side => 'left');
&Tk::MainLoop;