You can also use get:

use Tk;

my $top = new MainWindow;
my $t = $top->Text()->pack();
my $b = $top->Button(-text=>"OK",-command=>\&get_it)->pack();
MainLoop;

sub get_it {
    my $text = $t->get(0.1,"end");
    print "$text\n";
}
[download]

Hope this does what you want :)
mawe