It's not entirely clear, to me anyways, what you are trying to do, but there is also JComboBox.

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

#see also Tk::Spinbox 

my @choices;
my $index;
foreach my $f ( 'A' .. 'Z' ) {
    foreach my $s ( 'A' .. 'Z' ) {
        push @choices, "$f$s";
    }
}

my $mw  = MainWindow->new();
my $jcb = $mw->JComboBox(
    -relief             => 'groove',
#    -popuprelief        => 'groove', 
    -mode               => 'editable',
    -validate           => 'match',
    -highlightthickness => 0,
    -choices            => \@choices,
    -textvariable       => \$index,
    -selectcommand      => sub {
        print "Selected: $index\n";
    }
)->pack;

MainLoop;
#########################
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