#! /usr/bin/perl -w
# Set up some stuff for this example
use strict;
use Data::Dumper;
my %hash;
my @levels = qw(a b c);
my $value = 5;

# The next three lines are the essence:
my $work = \\%hash;
$work = \$$work->{$_} for @levels;
$$work = $value;

# Show that it worked
print Dumper(\%hash);

##</code><code>##

my $hash;

my $work = \$hash;
$work = \$$work->{$_} for @levels;
$$work = $value;

##</code><code>##

$hash{join(",", @levels)} = $value;