$ perl -Mstrict -Mwarnings -E '
    my @items_to_print_outside_loop;
    my %a=();

    $a{1}{"a"}{"A"}="FIRST";
    $a{1}{"c"}{"B"}="THIRD";
    $a{1}{"b"}{"C"}="SECOND";

    foreach my $k1 ( sort keys %a ) {
      foreach my $k2 ( sort keys %{$a{$k1}} ) {
        foreach my $k3 ( sort keys %{$a{$k1}{$k2}} ) {
         push @items_to_print_outside_loop, "$a{$k1}{$k2}{$k3}";
        }
        
      }
    }

    print join("\n", @items_to_print_outside_loop), "\n";
'
FIRST
SECOND
THIRD