#!/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;

##</code><code>##

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

##</code><code>##

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