$VAR1 = [
          undef,
          undef,
          undef,
          [
            undef,
            undef,
            undef,
            undef,
            undef,
            [
              'foo'
            ]
          ]
        ];

##</code><code>##

$VAR1 = {
          '3' => {
                   '5' => {
                            '0' => 'foo'
                          }
                 }
        };

##</code><code>##

perl -MData::Dumper -E '$A{3}{5}{0}="foo"; $v = $A{3}{5}; $v->{1}="bar"; die Dumper \%A'