Note that you don't have to pass the subroutine as an anonymous subroutine within a list reference.

That is to say, although it will work to do:

$mw->bind( '<Control-KeyPress-a>',   [sub {print "Button a has been pr
+essed\n"}] );
$mw->bind( '<Control-KeyRelease-a>', [sub {print "Button a has been re
+leased\n"}] );
[download]

One often specifies either a simple anonymous subroutine:

$mw->bind( '<Control-KeyPress-a>',   sub {print "Button a has been pre
+ssed\n"} );
$mw->bind( '<Control-KeyRelease-a>', sub {print "Button a has been rel
+eased\n"} );
[download]

or a simple anonymous list:

$mw->bind( '<Control-KeyPress-a>',   [ \&say_button_pressed,  "a" ]);
$mw->bind( '<Control-KeyRelease-a>', [ \&say_button_released, "a" ]);

# Unlikely to do it this way unless the following subroutines are
# longer, or likely to be called from multiple places...
#
sub say_button_pressed {
    printf "Button %s has been pressed\n", $_[0];
}
sub say_button_released {
    printf "Button %s has been released\n", $_[0];
}
[download]

I tend to use the former, an anonymous subroutine, when the code is brief and simple, whereas the latter is better when the subroutine is long and complex.

Thank you all. What is the rationale for having the syntax '<Control-KeyPress-a>' wouldn´t be more clear to write <KeyPress-Control-a>'?

It might well be more clear, but it doesn't work:

#!/usr/bin/perl -w
                                                                      
+          
use Tk;
                                                                      
+          
use strict;
use warnings;
                                                                      
+          
my $mw = new MainWindow();

$mw->bind( '<KeyPress-Control-a>', sub {print "Button a has been press
+ed\n"} );
$mw->bind( '<KeyPress-Control-a>', sub {print "Button a has been relea
+sed\n"} );

MainLoop;

# Produces ...
bad event type or keysym "Control" at
/usr/lib/perl5/site_perl/5.8.0/i386-linux-thread-multi/Tk/Derived.pm l
+ine 469.

# My version of Perl
This is perl, v5.8.0 built for i386-linux-thread-multi
[download]

---

s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/

I don't know anything about Tk. I haven't touched it ever. But I found a solution to this question in less than a minute. So all I have to say is RTFM.

use Tk;

my $mw = Tk::MainWindow->new( -title => "TEST");
  
$mw->bind( '<Control-KeyPress-a>', [sub {print "Button a has been pres
+sed\n"}] );
$mw->bind( '<Control-KeyRelease-a>', [sub {print "Button a has been re
+leased\n"}] );

MainLoop;
[download]

Update: Oh, I forgot about the keysym list. Well, doing a locate keysym showed up /usr/X11R6/include/X11/keysymdef.h. You may have to install a development package to get it (in Debian, it's x-dev).

# Binding two things to the same subroutine
my $print_sub = sub {print "Button A event\n"};
$mw->bind( '<KeyPress-a>', [ $print_sub ] );
$mw->bind( '<KeyRelease-a>', [ $print_sub ] );
[download]