Question

I would like to start with an empty hash, and then insert hash of hashes of the same kind into the hash.

#!/usr/bin/perl

use strict;
use warnings;

my %h = {};

$h{"1"} => {
    a => -1,
    b => -1,
    c => [
    {
        d => -1,
        e => -1,
    },
    ],
};

However this gives

Useless use of hash element in void context at ./hash.pl line 8.
Useless use of anonymous hash ({}) in void context at ./hash.pl line 8.
Reference found where even-sized list expected at ./hash.pl line 6.

It is sort of a database I would like to make, where I can insert the delete structures of the $h{"1"} kind.

Any ideas how to do this?

Answer 1

To initialize a hash you use %h = ().
{} is a reference to an empty anonymous hash. Try this:

my %h = ();

$h{"1"} = {
    a => -1,
    b => -1,
    c => [{
        d => -1,
        e => -1,
    }],
};