If you want to change the action of the button every time it is pressed, then you need to leave out the -command switch and bind the 'ButtonPress' action later. This will allow you to re-bind the action once you have pressed the button. Here's an example:

#!/usr/bin/perl

use strict;
use warnings;
use Tk;

my $main = MainWindow->new;

my $text = $main->Scrolled('Text', 
               -width=>'50'
              )->pack;

my $button = $main->Button(-text=>'next',
              )->pack;

$button->bind('<ButtonPress>', \&one);

MainLoop;

sub one
  {
    my $talk="One! Click for two.\n";
    $text -> insert('1.0',"$talk");
    $button->bind('<ButtonPress>', \&two);
  }

sub two
  {
    my $talk="One! Click for three.\n";
    $text -> insert('1.0',"$talk");
    $button->bind('<ButtonPress>', \&three);
  }

sub three
  {
    my $talk="One! Click for one.\n";
    $text -> delete('1.0', 'end');
    $text -> insert('1.0',"$talk");
    $button->bind('<ButtonPress>', \&one);
  }
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Cheers!

--
hiseldl
What time is it? It's Camel Time!