In Perl, there are 3 different kinds of hashes.

• A regular hash, which is defined by the % and ( ) characters - %hash = ( );
• A reference hash, which is defined with the $ and { } characters = $hash = { };
• A hash array, which is defined with the % and [ ] characters - %hash = [ ];

Let's say you a hash named %hash which contains two keys, foo and bar. Both keys are arrays, as indicated by the [ ] characters.

my %hash = ( 'foo' => [ 'John Doe', 'Jane Doe' ], 'bar' => [ 'Engineer', 'Sales' ] );

Dumper can be used to display the structure of the hash.

use Data::Dumper;
print Dumper \%hash;

Which should return something like this.

$VAR1 = {
          'bar' => [
                     'Engineer',
                     'Sales'
                   ],
          'foo' => [
                     'John Doe',
                     'Jane Doe'
                   ]
        };

Here is how you would loop through the top level keys.

foreach my $key (keys %hash) {
  print "$key \n";
}

Which should return the following.

foo
bar