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

my $tl;
my $mw = MainWindow->new;
$mw->title( "MainWindow" );
$mw->Button( -text => "Toplevel", -command => \&do_Toplevel )->pack();

MainLoop;

sub do_Toplevel {
	if ( !Exists( $tl ) ) {
		$tl = $mw->Toplevel();
		$tl->geometry('300x100+100+100');
		$tl->title( "Toplevel" );
		#put all your widgets here
				
		$tl->Button(
			-text    => "Close",
			-command => sub { $tl->grabRelease;
			                  $tl->withdraw }
		)->pack;
	}
	else {
		$tl->deiconify();
		$tl->raise();
		$tl->grabGlobal;
	}
}