use warnings;
use strict;
use Tk;

my $num = 0;

my $mw = tkinit();
my $button = $mw->Button(-text => $num)->pack();
$button->bind('<Button-1>', \&buttonPressed);
$mw->MainLoop();

sub buttonPressed{
	#this subroutine should be executed if the button is clicked once,
	#or repeatedly executed if the button is held down.
	print ".";
	$button->configure(-text =>	$num++);
}