You can't use focusCurrent(or whatever ) because you change your focus when you click the do_it button. So you have 2 choices, you can use an alternate method to launch the sub, as I show with a right-mouse click. It is usually done this way. Listbox has default bindings for the left-click, so I used the right. Also you want to check out how the -exportselection works, when you have a couple of listboxes.

Now if you want to keep the do_it button, you will have to save which listbox was last clicked in a variable.

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

my $lastactive = '';

my $mw = MainWindow->new;
my $lb1 = $mw->Scrolled('Listbox',
              -exportselection => 0,
           )->pack;

my $lb2 = $mw->Scrolled('Listbox',
             -exportselection => 0,
           )->pack;

my $b = $mw->Button(-text=>"doit",
            -command=>sub{&do_it1})->pack;

for(0..10){
    $lb1->insert($_,$_);
    $lb2->insert($_,$_);
           }

$lb1->bind( '<ButtonPress-1>', sub{$lastactive = 1} );
$lb2->bind( '<ButtonPress-1>', sub{$lastactive = 2} );

$lb1->bind( '<ButtonPress-3>', [\&do_it, 1 ] );
$lb2->bind( '<ButtonPress-3>', [\&do_it, 2 ] );


MainLoop;
################################################################ 
sub do_it {
   my( $object, $selbox ) = @_;

   my $i1 = $lb1->index('active');
   my $i2 = $lb2->index('active');
   print "selbox->$selbox lastactive->$lastactive $i1 $i2 \n";
}
################################################################ 
sub do_it1 {

   my $i1 = $lb1->index('active');
   my $i2 = $lb2->index('active');

    print "lastactive->$lastactive $i1 $i2 \n";
}
[download]

Here is a really simple-minded extension of the code you posted, which should demonstrate what you're looking for:

#!/usr/bin/perl

use strict;
use Tk;

my @list1 = qw/one two three four five six seven eight nine/;
my @list2 = qw/green blue red yellow orange black brown white purple/;

my $list_used;
my $mw = MainWindow->new;
my $lb1 = $mw->Scrolled('Listbox')->pack;
my $lb2 = $mw->Scrolled('Listbox')->pack;
my $b = $mw->Button(-text => "do it", -command => \&do_it)->pack;

$lb1->insert( 'end', @list1 );
$lb2->insert( 'end', @list2 );

MainLoop;

sub do_it
{
    if ( $lb1->curselection ) {
        print " got item from lb1: ",$lb1->get($lb1->curselection),$/;
    }
    elsif ( $lb2->curselection ) {
        print "  got item from lb2: ",$lb2->get($lb2->curselection),$/
+;
    }
    else {
        print "Nothing was selected\n";
    }
}
[download]

Asking a question is harder than I hoped. The solution above solved my problem; curselection was the magic word. It has only one problem: If the list has 1 item
 if ( $lb1->curselection ) {
will be false. I changed it to
 if ($lb1->curselection)>=0 ) {
but this generates an error message when the listbox is not selected. For the rest it works fine.

Thanks for all the help, F.