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 have a regular hash named %hash and the regular hash contains a single key with a single value.

my %hash = ( 'foo' => 'bar' );

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

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

Which should produce the following.

$VAR1 = {
          'foo' => 'bar'
        };

Here is how to print the value associated with department_key.

print "$hash{foo} \n";

Which should print the following.

bar

White space

Let's say the hash key contains white space. In this example, there is a single white space in "foo bar".

my %hash = ( 'foo bar' => 'Hello World' );

When there is white space, the key must be wrapped in single quotes.

print "$hash{'foo bar'} \n";

Special characters

Let's say the hash contains the forward slash character.

my %hash = ( '/' => 'bar' );

And you attempt to print the hash without wrapping the forward slash character in single quotes.

print "$hash{/} \n";

Should return something like this.

Search pattern not terminated at foo.pl line 8.

Certain special characters, such as the forward slash, must be wrapped in single quotes.

print "$hash{'/'} \n";

Variables

Variables can be used instead of strings.

my $key = "foo";
print "$hash{$key} \n";

Multidimensional

Let's say the hash is multidimensional. 

my %hash = ( 'foo' => { 'bar' => 'Hello World' } );

Dumper should return the following.

$VAR1 = {
          'foo' => {
                     'bar' => 'Hello World'
                   }
        };

Here is how you would print the value of the "bar" key.

print "$hash{foo}->{bar} \n";