As was said above, use the Scrolled widget.

#!/usr/bin/perl
use strict;
use Tk;
use Tk::ROText;

my $file = shift || $0;
open (FH,"< $file") or die "$!\n";
my @lines = <FH>;
close FH;

my $main = MainWindow->new;

my $text = $main->Scrolled('ROText',
   -width => 80, 
   -height => 30,
   -bg=>'black',
   -fg=>'lightyellow',
   -scrollbars => 'osow',
   ) ->pack();

 foreach my $line (@lines){
   $text->insert('end',$line);
   $text->update;
  }


$main->Button(-text => 'Cancel',
              -command => sub{exit}
               )->pack;

MainLoop;
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