$exit_frame->Button(-text => "Track",
        -command => [ \&track_changes, ($listbox, $output, $report_type) ])->pack;

##</code><code>##

$exit_frame->Button(-text => "Track",
        -command => [ \&track_changes, ($listbox, \$output, \$report_type) ])->pack;

##</code><code>##

sub track_changes {
        my ($listbox, $output_ref, $report_type_ref) = @_;
        my @files = $listbox->curselection;
        for (@files) {
                my $file = $listbox->get($_);
                print "$file\n";
        }
        print "$$output_ref\n";
        print "$$report_type_ref\n";
}