Local and global variables

As we shall see later, variables declared with my exist only for a certain area (scope) or your program. Sometimes though you may wish to have a global variable, which is visible throughout your program. There are at least two ways to do this:

• declare the variable with our, such as

  our $global_variable;
  

  In older Perl programs, you may see the construction

  use vars qw($global_variable);
  

  which (almost) does the same thing.
• For variables which are constant (ie, don't change within your program), you can declare them as in this example:

  use constant PI => 3.1415926539;
  

  Note that a dollar sign does not precede the variable name. Such variables cannot be altered in the course of your program.