use warnings;
use strict;
use Tk;

my $top = MainWindow->new;

$top->Button(
    -text => 'Push Me',
    -command => \&mysub
)->pack;

$top->bind('<Return>', \&mysub);

MainLoop;

sub mysub{
    $top->Label(
        -text => 'You pressed it!'
    )->pack;
}