#!/usr/bin/perl
use strict;
use Tk;
use IO::Handle;

my $H=IO::Handle->new;
open($H,"tail -f -n 50 z.txt |") or die $!;

my $main = MainWindow->new;

my $t = $main-> Scrolled('Text',
              -wrap=>'none')->pack(-expand=>1);

$main->fileevent(\*$H,'readable',[\&fill,$t]);

MainLoop;

sub fill {
  my ($w) = @_;
  my $text;
  my $text =<$H>;
  $w->insert('end',$text);
  $w->yview('end');
}