G'day loris,

Hash keys have no inherent order. If you want to retain the order you've shown, you'll need to specify it explicitly.

Here's two solutions in the one script. Pick whichever is most appropriate for you.

#!/usr/bin/env perl

use 5.010;
use strict;
use warnings;

my $animals = {
    gnu => {
        humps => 0,
    },
    dromedary => {
        humps => 1,
    },
    camel => {
        humps => 2,
    },
};

my @humps;
push @humps, $_->{humps} for map { $animals->{$_} } keys %$animals;
say "Unsorted humps: @humps";

my @sorted_animals = qw{gnu dromedary camel};
my @sorted_humps;
push @sorted_humps, $_->{humps} for map { $animals->{$_} } @sorted_ani
+mals;
say "Sorted humps: @sorted_humps";
[download]

Outputs:

$ pm_nested_hash_extract.pl
Unsorted humps: 2 0 1
Sorted humps: 0 1 2
[download]