Perl hashref of hashref

hashref-hashref.pl

#!/usr/bin/perl

use strict;
use Data::Dumper;

my $x;
$x->{a}->{b}->{c}->{d} = 1;
print Dumper($x)

=begin output
$VAR1 = {
          'a' => {
                   'b' => {
                            'c' => {
                                     'd' => 1
                                   }
                          }
                 }
        };
=end output