In PowerShell V2, functions got a lot more advanced.
They can do anything a Cmdlet can do. This is why advanced functions are sometimes called Script Cmdlets.
A function is considered advanced if it has a CmdletBinding attribute or any Parameter attributes.
Hopefully, that is not too advanced of a concept.
Let’s talk about a few big benefits of advanced functions.
The first little big thing you get by making a function advanced is the ability to mark a parameter as Mandatory.
A Mandatory parameter must be provided in order for a command to run.
The Object Pipeline is a major part of PowerShell.
We can use Parameter attributes to make a parameter bind to objects from the pipeline, and the process block to handle each object coming thru the pipeline.
function WhatDayOfTheWeek(
[Parameter(Mandatory,ValueFromPipeline)]
[DateTime]
$DateTime
) {
process {
$DateTime.DayOfWeek
}
}
Because PowerShell is type promiscuous, we can just supply a string with a date and PowerShell will turn it into a DateTime.
"12/31/2000" | WhatDayOfTheWeek
We can even provide a list of dates if we want to.
"07/04/1776", "09/28/1787" | WhatDayOfTheWeek
Property binding is what it sounds like.
We can make parameters in PowerShell bind to one or more properties.
We do this with the mouthful of a setting, ValueFromPipelineByPropertyName.
function NameAndAge {
param(
[Parameter(Mandatory,ValueFromPipelineByPropertyName)]
[string]
$Name,
[Parameter(Mandatory,ValueFromPipelineByPropertyName)]
[double]
$Age
)
process {
[PSCustomObject]$PSBoundParameters
}
}
Any object that has both an Age and Name property can be piped into this function
[PSCustomObject]@{
Name = 'James'
Age = 41
} | NameAndAge
We all know there’s more than one way to skin a cat (hopefully not from direct experience).
There also can be more than one way to run a command.
ParameterSets allow for various parameters to be grouped together.
function MoveDirection(
[Parameter(Mandatory)]
[double]
$Distance,
[Parameter(Mandatory,ParameterSetName='North')]
[switch]
$North,
[Parameter(Mandatory,ParameterSetName='South')]
[switch]
$South,
[Parameter(Mandatory,ParameterSetName='East')]
[switch]
$East,
[Parameter(Mandatory,ParameterSetName='West')]
[switch]
$West
) {
[PSCustomObject]@{
Distance = $distance
Direction = $psCmdlet.ParameterSetName
}
}
MoveDirection -Distance 1 -North