Let's say you create a hash named %hash, and you append a hash key value pair (department_key => engineering) and you also append an array of values (employees_key => John Doe and Jane Doe), like this.

my %hash = ( 'department_key' => 'engineering', 'employees_key' => [ 'John Doe', 'Jane Doe' ] );

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

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

Which should produce the following.

$VAR1 = {
          'department_key' => 'engineering',
          'employees_key' => [
                               'John Doe',
                               'Jane Doe'
                             ]
        };

You can loop through department_key . . .

foreach my $value ($hash{department_key}) {
  print "$value \n";
}

. . . and print the values.

engineering

You can loop through employees_key . . .

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

. . . and print the values.

John Doe
Jane Doe

key value pairs

In this example, the employees_key array contains key value pairs.

$VAR1 = {
          'employees_key' => [ 
                              {
                               'name_key' => 'John Doe', 
                               'department_key' => 'engineering'
                              }
                             ]
        };

If you do this . . .

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

Something like this will be returned.

HASH(0x2fd9bc8) 
HASH(0x5ac1b49)

When looping through an array that contains key value pair, you need to specify the keys, like this.

foreach my $value (@{$hash{employees_key}}) {
  print "$value->{name_key} \n";
  print "$value->{department_key} \n";
}

Which should print the values.

John Doe
engineering

Multidimensional

Let's say you have the following multidimensional hash.

my %hash = ( 'tomcat' => [ { 'dev' => [ { 'engineering' => [ { 'foo' => 'Hello', 'bar' => 'World' } ] } ] } ] );

Here is the Dumper output.

$VAR1 = {
         'tomcat' => [
                      {
                       'dev' => [
                                 {
                                  'engineering' => [
                                                    {
                                                     'foo' => 'Hello'
                                                    },
                                                    {
                                                     'bar' => 'World'
                                                    }
                                                   ],
                              }
                            ]
                     }
                   ]
        };

Here is how you could loop through the hash, printing the keys (tomcat, dev, engineering, foo, bar) and values (Hello World).

foreach my $platform (keys %hash) {
  print "platform key = $platform \n";
  foreach my $environment_key (@{$hash{$platform}}) {
    foreach my $environment (keys %$environment_key) {
      print "environment key = $environment \n";
      foreach my $department_key (@{$environment_key->{$environment}}) {
        foreach my $department (keys %$department_key) {
          print "department key = $department \n";
        }
        foreach my $data (@{$department_key->{$department}}) {
          foreach my $data_key (keys %$data) {
            if ($data_key eq "foo") {
              print "foo key contains a value of : $data->{foo} \n";
            }
            if ($data_key eq "bar") {
              print "bar key contains a value of : $data->{bar} \n";
            }
          }
        }
      }
    }
  }
}

Which should return the following.

platform key = tomcat
environment key = dev
department key = engineering
foo key contains a value of : Hello
bar key contains a value of : World