There are three built-in Perl Data Types: scalars, arrays and hash or associative arrays, that make the Perl language a powerful tool for text manipulation.

1. The first Perl data types is the scalar which is Perl’s data fundamental unit and it can be a single string, a number or a reference to a specific object.

When we speak about scalars, we have in view two types:

• scalar literals (or constants) that don’t change over the life of a program – one simple example is the value of pi
• scalar variables which let you hold data and manipulate them:
  • each variable is associated with a name that enables you to refer to the data and the address of a chunk of memory where the variable value is stored
  • the variable value can be changed during the execution of the program.

• Numbers can be integers or floating point decimal numbers expressed in different notations: 145.23, 22., 2.7E-2.
• Strings are sequences of characters and can contain any kind of data including simple ASCII text and binary data. There is no real limit for the size of a string literal. String literals are usually included between single or double quotes: '12.5', "Hello World!"

The name of a variable can contain any alphabetic characters, numbers or underscore. Note that the first character of a scalar variable name can’t be a number and the variable names are case sensitive, which means there is a significant difference between upper and lowercase characters. In Perl language it’s not necessary to declare a scalar variable, you just name and use it like in this scalar variable assignment example:

    $pi = 3.14;

to see a lot of fully commented examples that help you use the Perl statements and the Perl buit-in functions in your scripts.

    $a="Hello World!";
    $ref_a=\$a;
    print $$ref_a;

In the first line of code, the variable named $a stores the string “Hello World”. In the second line, the scalar variable ref_a is assigned with a reference to the variable $a (note that $a is preceded by the character \). The third line of the snippet is an example of how to print the string stored in the variable $a using a reference – we say that we dereference the scalar variable $ref_a before print. It’s a good practice to name a scalar reference beginning with the substring ref_, because this will tell you that this is a reference variable and if you want to use it, you must dereference it before.

Another kind of constants are literal lists which are used to initialize an array or a hash. To create a literal list it is very easy, just put a set of parentheses enclosing scalar values as in the following example:

    (1, 'hello', 'world', $a)

where we can see a list with 4 elements.

2. The second basic Perl data types is the array which is indexed by a number. For creating an array you simple must put something into it. It is not necessary to declare or specify its dimension. The name of an array begins with the character @ and in the example below we will assign the array @things with the literal list presented above:

    @things = (1, 'hello', 'world', $a);

3. The third basic Perl data types is the hash or associative array, which, like the array, contains a number of scalars. Hashes are indexed by strings and each hash has two parts: a key that identifies each element of the hash and a value which is the data associated with the key. The name of a hash structure begins with the character %. In order to assign a hash key, we’ll write it like in the following code line:

    $hash{$key}=value;

Here we have a short example of a hash structure called %NotebooksPrice:

    # We first assign some elements:

    $NotebookPrices{"Toshiba"}=650;
    $NotebookPrices{"HP"}=550;
    $NotebookPrices{"Acer"}=750;

    # we print now the keys of the hash %NotebookPrices
    foreach $item (keys %NotebookPrices)
    {
      print "$item\n";
    }

We tried above to enumerate some of the most important aspects of Perl data types, if you need more details, please check on CPAN or our link:

Perl Books and Tutorials

to see a lot of fully commented examples that help you use the Perl statements and the Perl buit-in functions in your scripts.