You should use strict!

This code prints the selected entry when you double click on the entry:

#!/usr/bin/perl

use strict;
use warnings;
use Tk;

# Variables
my $bx_w = 80;

my %hash = (

         "Test1" => [qw/a b c d/],
         "Test2" => [qw/e f g h/],
);

my $mw  = MainWindow->new();
$mw->title("test");
$mw->minsize(qw/79 4/);
#$mw->maxsize(qw/79 4/);

my $lz_f = $mw->Frame()->pack(-side =>'top',);

#&creation;

foreach my $label(keys %hash) {
    my $lngth = $#{$hash{$label}};
    my $lbl = $lz_f->Label(
        -text => $label,
        -bg => 'white',
        -width => $bx_w,
    )->pack(
        -side => 'top',
        -expand => 'both',
    );

    my $lstbx = $lz_f->Listbox(
        -bg=>'lightgrey',
        -relief=>'flat',
        -height=>$lngth,
        -width=>$bx_w,
    )->pack(
        -side=>'top',
    );

    foreach my $i ( 0 .. $#{ $hash{$label}} ) {
        $lstbx->insert($i, $hash{$label}[$i]);
    }

    $lstbx->bind( '<Double-1>' => sub{ my ($index) = $lstbx->curselect
+ion; print $lstbx->get($index) } );
}

MainLoop();
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