Better way of multiplayer IFs with PowerShell - powershell

Question

Im wondering if I am tackling this in the best way or if there is a better way of achieving my task.
I've written a function in PowerShell which takes different parameters, but some of the parameters won't work together.
So for example if I'm running the function and specifying a computerName parameter then I can't also pass list of multiple computer names.
I know I can write multiple If statements as along the lines if If(($computerName) - and ($computerList)){Then write and error}
but there are several parameters not just two, so do I need to do an if for each set of parameters someone could type in, or is there a better way of me tackling this?
currently I have multiple Ifs like If $computerName -and !(log file) and $computerlist) then write an error etc.

Answer 1

The PowerShell-idiomatic solution here is to declare a parameter that accepts either:
function Get-Stuff
{
param(
[Parameter(ValueFromPipeline = $true)]
[string[]]$ComputerName
)
process {
foreach($Computer in $ComputerName){
# do stuff with each individual -ComputerName argument
}
}
}
Now the user can do both
Get-Stuff -ComputerName oneComputerName
... and
"many","computer","names" |Get-Stuff
or for that matter
$computers = Get-Content .\Computers.txt
Get-Stuff -ComputerName $computers
# or
$computers |Get-Stuff
I know I can write multiple If statements as along the lines of If(($computerName) -and ($computerList)){Then write and error}
You can, but this is generally a bad idea - to test whether an argument value was passed to a parameter is better done through the automatic variable $PSBoundParameters:
function Get-Stuff
{
param(
[string]$AParameter,
[string]$ADifferentOne
)
if($PSBoundParameters.ContainsKey('AParameter')){
# an argument was definitely provided to $AParameter
}
if($PSBoundParameters.ContainsKey('ADifferentOne')){
# an argument was definitely provided to $ADifferentOne
}
}
The answer to the implied question of "how do I declare and work with mutually exclusive parameters" is parameter sets:
function Verb-Noun
{
param(
[Parameter(Mandatory = $true, ParameterSetName = 'SingleComputer')]
[string]$ComputerName,
[Parameter(Mandatory = $true, ParameterSetName = 'MultipleComputers')]
[string[]]$ComputerList
)
if($PSCmdlet.ParameterSetName -eq 'SingleComputer'){
# just one, we can deal with $ComputerName
}
else {
# we got multiple names via $ComputerList
}
}
PowerShell now recognizes two distinct parameter sets, each of which only accepts one of our parameters:
PS ~> Get-Command Verb-Noun -Syntax
Verb-Noun -ComputerName <string> [<CommonParameters>]
Verb-Noun -ComputerList <string[]> [<CommonParameters>]