oops sorry, I was unclear here. The hash looks like:

$hash{$key1}{$key2} = $value
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The subroutine 'retrieve_kv' already retrieves the other key and corresponding value, my question is how to put it in the loop, so that the keys retrieved are unique (there can be duplicates). Basically sth like:

do {
my ($key, $val) = retrieve_kv($hash{$k});
 } until (ALL 5 KEYS ARE UNIQUE);
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Hash keys are always unique, duplicates are impossible.

-> How do I post a question effectively?

Cheers Rolf

( addicted to the Perl Programming Language)

Rolf, I think the OP means something like this:

#!/usr/bin/perl -w

use strict;

use Data::Dumper;

use debug;

{
    my %tstinf = ();

    $tstinf{'Animal'}{'Mammal'}{'Domesticated'}{'Dogs'}{'Poodle'} = 1;
    $tstinf{'Animal'}{'Mammal'}{'Domesticated'}{'Dogs'}{'Greyhound'} =
+ 1;
    $tstinf{'Animal'}{'Mammal'}{'Domesticated'}{'Weasels'} = 1;
    $tstinf{'Animal'}{'Mammal'}{'Undomesticated'}{'Cats'}{'Siamese'} =
+ 1;
    $tstinf{'Animal'}{'Mammal'}{'Undomesticated'}{'Cats'}{'Calico'} = 
+1;
    $tstinf{'Animal'}{'Reptile'}{'Land'}{'Lizard'}{'Gekko'} = 1;
    $tstinf{'Animal'}{'Reptile'}{'Land'}{'Lizard'}{'Salamander'} = 1;
    $tstinf{'Animal'}{'Reptile'}{'Land'}{'Tortoise'}{'Spengleri'} = 1;
    $tstinf{'Animal'}{'Reptile'}{'Water'}{'Mocassin'}{'Blackhead'} = 1
+;
    $tstinf{'Animal'}{'Avian'}{'Bird'}{'Predator'}{'Raptor'} = 1;
    $tstinf{'Vegetable'}{'Ground Plant'}{'Edible'}{'Leafy'}{'Lettuce'}
+ = 1;

    my @unikey = &getUniqueKeys('', \%tstinf);

        print Dumper \@unikey;
}
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Use List::MoreUtils::uniq().

use strict;
use warnings;

use List::MoreUtils qw( uniq );

my %deck;

for my $suit (qw( Clubs Hearts Diamonds Spades )) {
    for my $rank (qw( 2 3 4 5 6 7 8 9 10 J Q K A )) {
        $deck{$suit}{$rank} = 1;
    }
}

$, = " ";
$\ = "\n";

# Prints 10 2 3 4 5 6 7 8 9 A J K Q
print sort { $a cmp $b } uniq map { keys $deck{$_} } keys %deck;
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