First, don't use prototypes unless you know why you need them. Also, in Perl, you do not need to pre-declare your subroutines like you do in C for instance.

Now, you were trying to use $planet as a hash reference, but it's actually a string (which you extract when you call keys %$h_ref. So, you have to pass in a reference to a hash in the call to base_code(), then inside the sub, you need to use the key name $planet as the key to the encompassing $h_ref to extract out the data you want:

use strict;
use warnings;

my %aas = (
    'serine' => ['TCA', 'TCC', 'TCG', 'TCT'],
    'proline' => ['CCA', 'CCC', 'CCG', 'CCT'] 
);

my %codes;
$codes{'earth'} = \%aas;
$codes{'mars'} = {
    'serine' => ['QWZ', 'QWX', 'QWW'],
    'proline' => ['ZXZ', 'ZXX', 'ZXQ', 'ZXW'] 
};
    
base_code (\%codes);

sub base_code {
    my $h_ref = $_[0];
    for my $planet (keys %$h_ref){
        for my $aa (keys %{ $h_ref->{$planet} }){
            for my $codon (@{ $h_ref->{$planet}{$aa} }){
                print $codon, "\n";
            }    
        }
    }
}

[download]

Output:

CCA
CCC
CCG
CCT
TCA
TCC
TCG
TCT
ZXZ
ZXX
ZXQ
ZXW
QWZ
QWX
QWW

[download]

In reply to Re: printing complex data structures by stevieb
in thread printing complex data structures by ic23oluk

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