How do I make a hash of hashes?

[vroom]

How do I make a hash of hashes?

Originally posted as a Categorized Question.

[blackfrier]

You can declare it like:

%hash = (
         arms => {
                  biggest  => 'mine',
                  smallest => 'yours'
                 },
         feet => {
                  biggest  => 'right',
                  smallest => 'left'
                 },
         legs => {
                  biggest  => 'theirs',
                  smallest => 'them',
                  muscular => 'yes'
                 }
     );

[chromatic]

You can also add a hash by doing something like this:

$hash{toes} = { 
    biggest => 'hairy troll',
    smallest => 'toddler',
};

(Note that the {} make a reference to an anonymous hash. See perlman:perldsc for more gritty details.)

[Doraemon]

This might interest you:

$other_hash{key} = '';

$hash{other} = \%other_hash; 
$hash{other}->{key}             = '1'; # ok
$tmp = $hash{other}; $$tmp{key} = '2'; # use it like this
# $$hash{other}{key}            = '2'; # but not like this
${$hash{other}}{key}            = '3'; # this is ok
$hash{other}{key}               = '3'; # this too, -> unneeded after {
+}

[da w00t]

If it was declared as a named hash of multiple dimensions, you may access it like $hash{foo}->{bar}->{beer}="free";, or like this: $hash{foo}{bar}{beer}="free"; if you prefer to drop the arrows.

If it's an anonymous hash held in a hash reference, you access it like this:

$r_hash->{foo}{bar}{beer}= "free";

[Doraemon]

Ahh, sorry! Not 'reference to anonymous hash', but 'reference to hash'.

Originally posted as a Categorized Answer.