$hash{subdir 1}
  $hash{subdir 2}{subsubdir 2.1}
  $hash{subdir 2}{subsubdir 2.2}
  $hash{subdir 3}{subsubdir 3.1}
  $hash{subdir 3}{subsubdir 3.1}{subsubsubdir 3.1.1}
  $hash{subdir 3}{subsubdir 3.1}{subsubsubdir 3.1.2}
  $hash{subdir 3}{subsubdir 3.1}{subsubsubdir 3.1.3}

##</code><code>##

  @parts=split /\//,$dirname;
  %hash{ @parts } = (); ## this doesn't work, of course, 
                        ## just an example of the idea

##</code><code>##

  $hash{foo}=1;
  $hash{foo}{bar}=2;

##</code><code>##

#!/usr/bin/perl

use strict;
use Data::Dumper;

my %hash;

$hash{foo}=[undef,1];
$hash{foo}[0]{bar}=[undef,2];
$hash{foo}[0]{bar}[0]{bink}=[undef,4];

print Dumper \%hash;