There are three basic variable data types in Perl: scalars, arrays, and hashes.

Scalars are single numbers or strings, delineated by a dollar sign ($).

Example:

$data, $this_number

Arrays contain two or more scalar data elements. An array is denoted by the "at" sign (@). The term 'array' in Perl really refers to a scalar array, or list.

Example:

@desk_items = ("pencil", "pen", "calculator", "keyboard", "coffeepot");

Shortcut: Perl allows you to put quotes around individual array elements using the qw construct. The above array declaration then becomes

@desk_items = qw(pencil pen calculator keyboard coffeepot);

The parentheses aren't necessary; (almost) any character can be used as a delimiter.

@desk_items = qw/pencil pen calculator keyboard coffeepot/;

is just as valid.

Array elements are accessed using the dollar sign ($) and square brackets ([ ]), with the first array element being 0 by default:

$desk_items[1] = "pen";

Multidimensional arrays do not exist as such in Perl. However, since a multidimensional array (also called a matrix) is in effect an array of lists, you can make use of Perl's anonymous array to do the same job (it's called an anonymous array because you don't assign a scalar reference to it).

Example:

@dogs=("toy", [chihuahua, yorkie, peke],
       "miniature", [dachshund, poodle, beagle],
       "standard", [lab, afghan, dane]
);

To dereference the anonymous array elements, use the arrow (infix) operator ->:

print "My dog is a $dogs[1] $dogs[1]->[0].\n";

This should produce the following output:

My dog is a miniature dachshund.

Hashes (also called associative arrays) are pairs of scalars referred to as keys and values. Obviously, hashes should contain even numbers of scalars, because each key must have a value and vice-versa (however, if Perl encounters a key with no corresponding value, it simply regards that value as undefined). Hashes are denoted by the "percent" sign (%).

Example:

%dogs=('T','toy','M','miniature','S','standard');


In this example, T, M, and S are the keys; toy, miniature, and standard are the values.

For the sake of clarity and ease of reference, Perl provides an alternate notation system for hash elements that uses the arrow operator =>:

%dogs=(
	'T'=>'toy',
	'M'=>'miniature',
	'S'=>'standard'
);

Hash elements are accessed using curly braces ({ }):

print "My dog is a $dogs{'M'} dachshund\n";

Which produces the output

My dog is a miniature dachshund

In much the same way that anonymous arrays can be used to provide multidimensionality for lists, the anonymous hash may be employed to nest hashes.

Example:

%pets=(
	'dog' => {
	    'toy' => 'peke', 
	    'miniature' => 'dachshund',
	    'standard' => 'lab'
	},
	'cat' => {
	    'shorthair' => 'tabby' 
	    'longhair' => 'persian',
	    'curlyhair' => 'rex'
	}
);

To dereference nested hash elements, use the infix operator ->:

print "My pet is a $pets{'cat'}->{'shorthair'} cat\n";

Which produces

My pet is a tabby cat

Finally, you can also construct an array of anonymous hashes:

@pets=( 
	{
	'type'=>'dog',
	'breed'=>'dachshund',
	'color'=>'black and tan'
	},
	{
	'type'=>'cat',
	'breed'=>'tabby',
	'color'=>'orange'
	}
);

Access nested hash elements in this array using a combination of the syntaxes for arrays and hashes:

print "My pets are a $pets[0]{'color'} $pets[0]{'breed'} $pets[0]{'type'} 
      and an $pets[1]{'color'} $pets[1]{'breed'} $pets[1]{'type'}\n";

This will produce

My pets are a black and tan dachshund dog and an orange tabby cat