If you really need to type things in manually, try this:

my %hash =
( "Abe" => 
    { "lastname" => "Lincoln", 
      "friends" => 
        { "George" => 
            { "lastname" => "Washington", 
              "wife"     => "Martha"
            }
          "James" =>
            { "lastname" => "Madison", 
              "wife"     => "Dolly"
            }
        },
    },
  "Franklin" =>
    { "lastname" => "Roosevelt", 
      "wife" => "Eleanor"
    }
)
[download]

However, if you have some structure, you'll want to stuff these programmatically, instead of retyping all of the keys.

There are several ways to do this. The most direct is to create a sub to navigate the hash for you. The sub will take a hash ref, a value, and a list of keys. The value may itself be a hash(ref), so you can nest these and use loops and so forth.

For example:

#!/your/perl/here

use strict;
use warnings;
use Data::Dumper;

sub update_hash
{
    my ($h, $value, @keys) = @_;
    for my $key (@keys[0..$#keys-1])
    {
        $h = $h->{$key};
    }
    $h->{$keys[-1]} = $value;
}

# build up a hash from scratch

my %hash;
update_hash(\%hash, {}, 'one');
update_hash(\%hash, {}, 'one','two');
update_hash(\%hash, 123, 'one','two','three');

# don't have to start at the top
update_hash($hash{one}{two},129,'nine');
update_hash($hash{one}{two},{},'zero');
update_hash($hash{one}{two},1208,'zero','eight');

print Dumper(\%hash);

__OUTPUT__
$VAR1 = {
          'one' => {
                     'two' => {
                                'three' => 123,
                                'zero' => {
                                            'eight' => 1208
                                          },
                                'nine' => 129
                              }
                   }
        };
[download]

The OO approach is really just a group of setters/getters that grok your data structure. If you have a complicated and deeply-nested structure, you might want to do that just for your sanity -- otherwise, it's probably better just to write subs as needed.