Perl - Introduction to Subroutines
In a Nutshell - CIW Course Section 2, Part B2, Chapter 4
Overview of Subroutines
Once you get past the basics of Perl programming you will find subroutines invaluable. These named blocks of code avoid repetition of code, make your programs much more readable and allow passing of parameters to increase flexibility.
The advantages of subroutines include:
- Enhanced manageability of large scripts
- Reduce the total number of lines of code
- Accelerates script development
Many of the built-in functions with Perl are little more than pre-coded subroutines.
sub myFunction
{
print("Hello World");
}
The above example gives the basic syntax for declaring a subroutine. The subroutine name follows the 'sub' keyword and the block of code is contained in the following braces.
print(average(1, 3, 8, 2));
sub average
{
foreach $_ (@_)
{
$total += $_;
$i++;
}
$avg = $total / $i;
return $avg;
}
This example demonstrates the use of parameters. In this instance we have not declared the parameters so Perl assumes them from their usage. We have passed an array, or list, of values to the subroutine to calculate the average of the values. Note the use of the 'return' keyword to pass the end value back from the routine. In other languages, a routine that returns a value is called a function.
Scope of Variables
Perl variables are global in scope, meaning they have value throughout the whole of the code. Other languages keep variable declared within a subroutine as private to that routine. The 'my' operator permits this scope limiting in Perl, A variable declared as: 'my $myVar = 1;' will be local to the routine that it was declared in.
The 'use strict' pragma can direct the interpreter to ensure that all variables are declared with the 'my' operator. But this is a more advanced subject and will be covered later.