#!/usr/bin/perl

# https://perlmonks.org/?node_id=1226249

use strict;
use warnings;
use Tk;
use Tk::ROText;

my $message = '';
my $lb1pick = '';
my $lb2pick = '';

my $mw = MainWindow->new;
my $label = $mw->Label(
  -textvariable => \$message,
  )->pack();
my $lb1 = $mw->Listbox(
  -exportselection => 0,
  )->pack(-side => 'left');
my $lb2 = $mw->Listbox(
  -exportselection => 0,
  )->pack(-side => 'left');

$lb1->insert(end => qw( one two three four five ) );
$lb2->insert(end => qw( six seven eight nine ten ) );

$lb1->bind('<ButtonRelease-1>' => sub
  {
  $lb1pick = $lb1->get('active');
  $message = $lb1pick . '  ' . $lb2pick;
  });

$lb2->bind('<ButtonRelease-1>' => sub
  {
  $lb2pick = $lb2->get('active');
  $message = $lb1pick . '  ' . $lb2pick;
  });

MainLoop;