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

use Tk;

# Global variables
my $entry_val;

# Main Window
my $mw = new MainWindow;
$mw->Entry(
   -validate=>"all", 
   -validatecommand=>\&handleEvent, 
   -textvariable=>\$entry_val,
)->pack();

MainLoop;

# Callbacks
sub handleEvent {
   my ($new_val, $chars_2_change, $curr_val, $index, $action) = @_;

   # do nothing if No Change and No Force Validate
   if (!$chars_2_change && $action != -1){
      return;
   }

   # do something meaningful here.
   # for now, just print the $new_val
   print $new_val."\n";
}