Windows PowerShell 1.0 Functions

Windows PowerShell functions provide a way to organize scripts and promote re-use of code. They also provide a mechanism for creating custom cmdlets and filters. Windows PowerShell functions are easy to create and simple to use, as will be illustrated in the remainder of this chapter.

Creating and Calling a Simple Windows PowerShell Function

The most basic of Windows PowerShell functions are created using the function keyword following by the name of the function. Finally, the list of statements to be executed are enclosed in curly braces. For example, the following function simply output a string before returning:

function sayhello
{
    "Hello. Welcome to PowerShell Functions"
}

Having created a simple function, it can be called by referencing the function name:

PS C:\Users\Administrator> sayhello
Hello. Welcome to PowerShell Functions

Passing Parameters to a Function

In the preceding example, the function did not expect to be passed any parameters (also known as arguments). These are values which are entered on the command-line along with the function at the point that it is called. Windows PowerShell stores any parameters that were entered along with the function name in a special variable called $args. The $args variable is actually an array object with each parameter assigned to an array element (for more detailed information on working with arrays refer to the chapter entitled Working with Arrays in Windows PowerShell 1.0.

In order to demonstrate the use of the $args variable in the context of Windows PowerShell functions, the following function displays the number of parameters passed into the function, and then multiplies the first two parameters:

function multiply_numbers 
{
   "Number of parameters = " + $args.count
   $args[0] * $args[1]
}

When called with two parameters, the function generates the following output:

PS C:\Users\Administrator> multiply_numbers 4 2
Number of parameters = 2
8

Specifying Named Parameters

In the above example, we relied on the $args array to access any parameters which were passed through the function when it was called. Whilst this apprach works fine for simple functions, it can quickly become confusing as functions become more complex. An alternative mechanism is to declare the expected parameters and assign them variable names by which they may be accessed within the body of the function. This is achieved by placing the expected parameters in parentheses after the function name during the declaration. For example, the following function declares that two parameters are expected