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

my $value;

my $mw = MainWindow->new;

my $entry = $mw->Entry(
    -state        => 'readonly',
    -textvariable => \$value
)->pack;

my $lb = $mw->Listbox( -height => 0 )->pack;
$lb->insert( 'end', qw/one two three four five six/ );

$lb->bind( '<ButtonPress-3>', [ \&setItem, \$value, Ev('@') ] );

sub setItem {
    my ( $lb, $valSR, $xy ) = @_;

    $lb->selectionClear( 0, 'end' );
    my $index = $lb->index($xy);
    if ( defined($index) ) {
        $lb->selectionSet($index);
        $$valSR = $lb->get($index);
    }
}

MainLoop;