Hashes... Light switch isn't coming on

[agentorange]

Hi guys hoping you can help

For whatever reason that switch inside my head that turns on the light to say I understand hashes just will not flick on! It's possible that I'm running before I can walk as I've forced my way through understanding and retrieving data from complex hashes, and written good few bits of code in the last few months, but I just cannot get it into my head how to build those hashes unless I explicitly hard code them.

Can you assist with a sample piece of code that may finally enable me to crack it?

#!/bin/perl
#

use Data::Dumper;

my @primary = qw( foo bar );
my @secondary = qw( p0 p1 p2 );
my @tertiary = qw( itema itemb );

my %HoH;

foreach $primary( @primary )
{
    print "\t$primary\n";

    foreach $secondary( @secondary )
    {
        print "\t\t$secondary\n";

        foreach $tertiary( @tertiary )
        {
            print "\t\t\t$tertiary\n";

            %HoH = ( $primary => $secondary => $tertiary);
            #%HoH = {$primary}{$secondary} => $tertiary);
        }
    }
}

print Dumper \%HoH;

The basic debug output from the print should describe the hash I'm trying to create. That is a key of "primary", containing a key of "secondary" elements with elements of "tertiary".
ie.

     foo =>
                p0 =>
                        itema
                        itemb
                p1 =>
                        itema
                        itemb
                p2 =>
                        itema
                        itemb
    bar =>
                p0 =>
                        itema
                        itemb
                p1 =>
                        itema
                        itemb
                p2 =>
                        itema
                        itemb

But what I actually get is

$VAR1 = {
          'bar' => 'p2',
          'itemb' => undef
        };