Here's something to get you started ...

use strict;
use warnings;
use Tk;

my $mac_addr = "";

my $mw = new MainWindow(-title => 'Enter a MAC address');
my $fr = $mw->Frame()->pack(-expand => 1, -fill => 'both');
my $lb = $fr->Label(-text => "Enter MAC address ")->pack(-side => 'lef
+t');
my $en = $fr->Entry(-textvar => \$mac_addr)->pack(-side => 'left');
my $bt = $fr->Button(-text => 'Validate', -background => 'green');
$bt->configure(-command => sub { validate() });
$bt->pack(-side => 'left');
MainLoop;

sub validate {
    my $valid = '[0-9a-f]' x 2;
    if ($mac_addr =~ /($valid:){5}$valid/i) {
        print "Address '$mac_addr' is VALID\n";
    } else {
        print "Address '$mac_addr' is INVALID\n";
    }
}
[download]

Does that help you?

Thanks Liverpol, that should work. My problem was I was breaking the address into bytes, then displaying each byte as an entry widget, using a label widget with ':' in it as a separator. I couldn't get the entry widgets to show my numbers as hex, they kept getting converted to decimal.

This is what I had. I'm pretty new to this stuff, learning perl and tk as I go.

use strict;
use Tk;

# Take a 6 element array and make it string.

sub makeString {
   my @data = @_;

   my $result = sprintf "%02x:%02x:%02x:%02x:%02x:%02x",
               $data[0], $data[1], $data[2], $data[3], $data[4], $data
+[5];

   return $result;
}

sub doit {
   my @addy = @_;

   my $mw = MainWindow->new();

   # Show the current address
   my $current = makeString(@addy);
   $mw->Label(-text => $current)->pack(-side => 'top');

   # now build some entry widgets to change it
   for (my $i = 0; $i < 6; $i++) {
      $mw->Entry(-textvariable => \$addy[$i], -width => 3)
         ->pack(-side => 'left');
      $mw->Label(-text => ':', -width => 1)->pack(-side => 'left');
   }

   $mw->Button(-text => "Done", -command => sub {$mw->destroy;})
      ->pack(-side => 'bottom');
   MainLoop;
   return(@addy);
}

my @foo = (0x10, 0x22, 0x33, 0x4b, 0x5f, 0x6d);

print "Starting with: " . makeString(@foo) . "\n";
my @bar = doit(@foo);
print "Ended with: " . makeString(@bar) . "\n";
[download]

    "... learning perl and tk as I go"

Well, I'm impressed.  Learning Perl takes enough effort (though mostly fun :-D), and Tk is no simple discipline to master.  Good for you!

If you want to display hexadecimal, you could just use sprintf to reformat each hex pair before the assignment:

$mw->Entry(-textvariable => [ sprintf "%02x", $addy[$i] ], -width => 3
+)
   ->pack(-side => 'left');
[download]

Another minor suggestion:  check your loop variable so you don't print an extra ':' after the final byte:

if ($i < 5) {
    $mw->Label(-text => ':', -width => 1)->pack(-side => 'left');
}
[download]

---

s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/

What have you tried that's failing?

ug, I hate entering IP addresses in Windows's "[box].[box].[box].[box]". Can't paste. I'd go with a straight text box, and validate the input.