#!/usr/bin/perl
use Tk;
my $mw = new Tk::MainWindow;
my $btn = $mw->Button(-text => 'Hit Return')->pack();

# 
# Note that we *usually* bind to the main window, 
#  not the button - it's a focus thing. 
# 
$mw->bind('<Return>', \&_on_rtn);

MainLoop;
exit(0);

sub _on_rtn
    {
        $mw->messageBox(-message=>'Thanx for using the keyboard!');
            }