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

my $mw = MainWindow->new();

my $text_box = $mw->Scrolled("Text", 
                 -scrollbars => 'e',
                 -relief => 'sunken',
                 -takefocus => 1)
                 ->pack(-expand => 1, -fill => 'both');

for(1..1000){
$text_box->insert('end', "$_ test\n");
$text_box->see('end');
}

$text_box -> Subwidget("yscrollbar")->configure(
               -background => "lightgreen",
               -troughcolor => "black",
      #comment out the following line to restore normal
      #scroll function 
               -command => \&scrollcallback,
               );

MainLoop;

#if you specify a scrollcallback, you will override the 
#normal scroll behavior. 

sub scrollcallback{

#uncomment the following line to restore the normal function
#   $text_box->yview(@_); 

#do your additional stuff here
print "1\n";

}