#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $mw = MainWindow->new;
$mw->bind("<Key>",  sub { &pressed  } );

MainLoop;

sub pressed{
  print 'Key: ', ${Ev('K')}, " pressed\n";
  $mw->bind("<Key>",  sub { } );
  $mw->bind("<KeyRelease>",  sub {&pressed } );
}