if(ref($hash) eq 'HASH'){
        my $header = $hash->{'header'};
        while(my ($key, $value) = each(%$hash)){
             push(@stack, unpack_row($value, (@row, $key)));
        }
    }
    else {
        return([@row, $hash]);
    }

##</code><code>##

if(ref($hash) ne 'HASH'){
    return([@row, $hash]);
}

my $header = $hash->{'header'};
while(my ($key, $value) = each(%$hash)){
    push(@stack, unpack_row($value, (@row, $key)));
}

##</code><code>##

use strict;
use warnings;
use Data::Dumper;

sub unpack_row {
    my ($hash, @row) = @_;
    return [ @row, $hash ] unless (ref $hash eq 'HASH');
    return map { unpack_row($hash->{$_}, @row, $_) } keys %$hash;
}

my $hash = {
    foo => { bar => { bat => 5, bird => 2 } },
    goo => { tab => { bird => 2 } },
};

print Dumper($hash);
print Dumper(unpack_row($hash, ()));