Using Scalar Variables

<< Data Types: Values and Variables

<< Perl Tutorials - Herong's Tutorial Examples

This section describes how a scalar variable can be assigned with a scalar value. An unassigned scalar variable contains the (undef) value. The undef() function removes the assigned value from a scalar variable.

Scalar variables can be used in a Perl script under these rules:

• A scalar variable should be assigned with a scalar value constructor using an assignment operation. For example, $price = 19.99.
• A scalar variable without any scalar value assigned is an undefined variable and contains a special value called, undef.
• The assigned value can be removed from a scalar variable using the undef() function.
• A scalar variable can be used in a numeric operation, where the value contained in the scalar variable will be interpreted as a number.
• A scalar variable can be used in a string operation, where the value contained in the scalar variable will be interpreted as a string.
• A scalar variable can be used in a Boolean operation, where the value contained in the scalar variable will be interpreted as TRUE or FALSE.

See the previous section for scalar value interpretation rules.

Here are some examples of scalar variable assignment operations with scalar value constructors:

   $one = 1;
   $x = 8.8;
   $big = 1e+50;
   $pi = '3.14';
   $msg = 'hello';
   $cmd = 'dir \\home\\herong';
   $title = "Herong's Notes";

Here is a Perl tutorial script on how to use scalar variables:

#- ScalarVariable.pl
#- Copyright (c) 1995 by Dr. Herong Yang, http://www.herongyang.com/
#
   $price;                             # Undefined
   print($price, "\n");                # (blank)

   $price = 19.99;                     # Defined
   print($price, "\n");                # 19.99  

   $price = $price * 80/100;           # In an arithmetic operation
   print($price, "\n");                # 16.992

   $price = "Market price";            # Changed to a string value
   print($price, "\n");                # Market price

   $price = reverse($price);           # In a function call
   print($price, "\n");                # ecirp tekraM

   $shipping = 3.99;
   $price = $price + $shipping;        # Auto-converted to a number: 0
   print($price, "\n");                # 3.99

   undef($price);                      # Undefined again
   print($price, "\n");                # (blank)

Here is the output of the tutorial script:

19.99
15.992
Market price
ecirp tekraM
3.99

Sections in This Chapter

Scalar Values and List Values

Scalar Value Constructors

Scalar Value Interpretation

List Value Constructors

Variables - Scalar, Array and Hash

Using Scalar Variables

Using Array Variables

Using Hash Variables

"undef" Value and Undefined Variables