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

my @lst_files = (0...10);
my $file;

my $mw = new MainWindow;
my $frm1 = $mw -> Frame(-bg=>'LightSkyBlue1') -> pack(-fill => 'x');
my $frm11 = $frm1 -> Frame(-bg=>'LightSkyBlue1')->pack(-fill => 'x');
my $lst = $frm11 -> Scrolled('Listbox',
                              -width => 50,
                              -height => 5, 
                              -scrollbars => 'oe', 
                              -selectmode => 'single'
                             ) -> pack(-side => 'bottom');
$frm1 -> Button(-width => 15, -text => "fill", -command =>\&fill_boxes) -> pack(-side => 'top');
$frm1 -> Button(-width => 15, -text => "print", -command =>\&sample) -> pack(-side => 'top');
MainLoop;

sub fill_boxes
{
   $lst -> delete ('0.0', 'end');
   $lst -> insert('end', @lst_files);
}

sub sample
{
      if($lst->curselection ne '') # <- Error msg points here
      { 
         #Extract Application File Selection
         $file = $lst -> get($lst -> curselection);
         print "$file\n";
      }
# and then more happens
}