my %a;
$a{key1}{a}{key2}{b}{key3}{c}{key4}{d}=1;
$a{key1}{a}{key2}{b}{key3}{d}{key4}{c}=1;
foreach my ($a, $b, $c, $d)
(keys_it $a{key1}{*}{key2}{*}{key3}{*}{key4}{*})
{
 whateveryouwant with your elements of %a;
}

##</code><code>##

foreach my $key1 (keys %{$a{key1}...})
{
my $level1=$a{key1}{$key1};
 foreach my $key2 (keys %{$level1->{key2}})
 {
  ...
 }
}

##</code><code>##

%a={a => {b => c}, b => 3};
open FILE, "myhash.txt";
print FILE Dumper (%a);
cloes FILE