Here's an example:

#!/usr/local/bin/perl -w
use Tk;
use strict;

my $mw = MainWindow->new();

my $button = $mw->Button();
$button->configure(-text => 'DISCONNECTED',
                   -command => sub { do_connect($button) });
$button->pack();

MainLoop();


sub do_connect {
        my $button = shift;
        $button->configure(-text => 'CONNECTED');
}
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FYI: there's a nice newsgroup devoted to Perl/Tk!