use Tk;

my $top = MainWindow->new();
$top->bind("<KeyPress>" => [\&click,Ev('K')]);
sub click {
    my ($window, $button) = @_;
    if ($button eq 'Control_L') { # ignore left Ctrl
        print "I don't do anything";
    } else { 
        print $button;
    }
}
MainLoop();
[download]