Question

How come I never see examples like these where you declare the hash, and then put then inside another hash?

my %hash1={};
$hash1{'key1'}='1-111';
$hash1{'key2'}='1-222';
$hash1{'key3'}='1-333';
my %hash2={};
$hash2{'key1'}='2-111';
$hash2{'key2'}='2-222';
$hash2{'key3'}='2-333';

my %main_hash1={%hash1, %hash2};

I’ve only seen examples like these where they put the hashes inside the hash, instead of a variable for the hash:

my %main_hash2=( 'hash1' => {
                            'key1' => '1-111',
                            'key2' => '1-222',
                            'key3' => '1-333'
                    },
             'hash2' => {
                            'key1' => '2-111',
                            'key2' => '2-222',
                            'key3' => '2-333'
                    }
);

(similar with arrays also)

Answer 1

You can’t store a hash in a hash, you can store a hashref in a hash though:

my %main_hash1 = ( hash1 => \%hash1, hash2 => \%hash2 );

The same goes with arrays:

my @main_array1 = ( \@array1, \@array2 );

And with mixes:

my @array_of_hrefs = ( \%hash1, \%hash2 );
my %hash_of_arefs = ( arr1 => \@arr1, arr2 => \@arr2 );

This is done all the time; I don’t know why you haven’t seen it and I doubt anyone on SO would know that answer.

Also, this does not initialize a hash:

my %hash1={}; ## should be my %hash1; or my %hash1 = ();