Close. Keep track of a reference to the reference.

my %hash;

while (<>) {
  chomp;
  my ($key, $val) = split(/=/, $_, 2);
  my @elts = split(/\./, $key);

  my $p = \\%hash;
  $p = \( ${$p}->{$_} ) for @elts;

  $$p = $val;
}

use Data::Dumper;
print Dumper(\%hash);
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Tested.

Wow, that's awesome. I'd been wondering for last few hours on the best way of doing it... thank you so much!

Couple of follow-up questions: 1. Could you please explain what the following snippet does?

     my $p = \\%hash;
     $p = \(${$p}->{$_}) for @elts;
     $$p = $val;
[download]

2. Is there a quick/easy way to change the key of a hash? Apologies if I'm breaking a rule here (double/cross-posting)...

Umm... it gives you that button to "update"?