In Perl, there are 2 different kinds of hashes.

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

Let's say you a hash named %hash which contains a single key (foo), and the key is an array, as indicated by the [ ] characters.

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

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

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

Which should return something like this.

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

Here is how you would loop through the values in the foo key.

foreach my $foo (@{$hash{foo}}) {
  print "$foo \n";
}

Which should return the following.

John Doe
Jane Doe

Let's say you a hash named %hash where the bar key is a child of the foo key, which means the hash is multidimensional. In this example, the bar key is an array, as indicated by the [ ] characters.

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

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

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

Which should return something like this.

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

Here is how you would loop through the values in the bar key.

foreach my $value (@{$hash{foo}->{bar}}) {
  print "$value \n";
}

Which should return the following.

John Doe
Jane Doe

Multiple Arrays

Let's consider the scenario where there are multiple arrays in the hash. Let's say you have the following, where the foo key is an array, and the bar key which is also an array is within the foo key.

my %hash = ( 'foo' => [ { 'bar' => [ 'John Doe','Jane Doe' ] } ] )

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

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

Which should return something like this.

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

And here is how you would loop over the values in the bar key.

foreach my $foo (@{$hash{foo}}) {
  foreach my $value (@{$foo->{bar}}) {
    print "$value\n";
  }
}

Which should return the following.

Hello
World