my %inner_hash = ( dir => '/tmp/foo/', filename => 'bar.txt' );
my %hash_of_hashes = ();

$hash_of_hashes{'baz'} = \%inner_hash; # Backslash = reference to

print "The filename associated with 'baz' is "  .$hash_of_hashes{'baz'}->{'filename'} . "\n";