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

my $mw = MainWindow->new(-title => 'Mac Address Input Example');
my $fr = $mw->Frame()->pack(-expand => 1, -fill => 'both');
my $lb = $fr->Label(-text => 'MAC Address')->pack(-side => 'left');

my %entries;
for(1..6){
  $entries{$_}{'entry'} = $fr->Entry();
  $entries{$_}{'entry'}->configure(
    -textvariable    => \$entries{$_}{'addy'},
    -width           => 3,
    -validate        => 'focusout',
    -validatecommand => [ \&validate,$_ ],
    -invalidcommand  => [ \&show_invalid,$entries{$_}{'entry'} ],
  );
  $entries{$_}{'entry'}->pack(-side => 'left');

}

MainLoop();

# returns `1' if valid, and `0' if invalid
sub validate {
  my($num,$val) = @_;
  unless($val){ print "Field $num has nothing to validate\n";return 1;}

  my $valid = ($val =~ /^[0-9a-f]{1,2}$/i) ? 1 : 0;
  printf "Field %s, validating \`%s'...%s\n",$num,$val,$valid? "ok": "FAILED";

  return $valid;
}

sub show_invalid {
  my($widget) = @_;
  $widget->focus();

  # temporarily flash the background of the problem field in red
  my $bg = $widget->cget('-bg');
  $widget->configure(-bg => 'red');
  $widget->update();

  # effect a sleep of 200 milliseconds
  select(undef,undef,undef,0.2);

  # return the background color to the original state
  $widget->configure(-bg => $bg);
  $widget->update();
}



##</code><code>##

for(1..6){
  $entries{$_}{'addy'} = 'zz'.$_ if($_ == 3);