Perl Scalars

What is a scalar variable?

• You can think of a variable as a "place holder", or a "name" that represents one or more values. The generic syntax for defining scalar variables (also known as variables for short) is as follows:

  $variable_name = value; 
  

• Thus, for example, we might assign the value of twenty-seven to the scalar variable named "age" with the syntax:

  $age = 27; 
  

• The dollar sign ($) is used to let Perl know that we are talking about a scalar variable. From then on, unless we change the value of $age, the script will translate it to twenty-seven.

• So if we then say:

  print "$age\n"; 
  

• Perl will send the value "27" to standard output, which in our case, will be the Web browser.

• If we are assigning a word or a series of words to a scalar variable rather than just a number, we must mark the boundary of the value with single or double quotes so that Perl will know "exactly" what should be assigned to the scalar variable.

• We use single quotes to mark the boundary of a plain text string and we use double quotes to mark the boundary of a text string that can include scalar variables to be "interpolated". For example, we might have the following lines:

  $age = 27; 
  $first_name = 'Selena'; 
  $last_name = 'Sol'; 
  $sentence = "$first_name $last_name is $age"; 
  print "$sentence\n"; 
  

• The routine would print the following line to standard output:

  Selena Sol is 27 
  

• Notice that the scalar variable $sentence is assigned the actual values of $first_name and $last_name. This is because they were "interpolated" since we included them within double-quotes in the definition of $sentence. There is no interpolation inside single quotes. Thus, if we had defined $sentence using single quotes as follows:

  $sentence = '$first_name $last_name is $age'; 
  

• Perl would print the following to standard output:

  $first_name $last_name is $age 
  

Exercise Three
Table of Contents
Using Scalars