Parameter Sets: Require specific combinations of Parameters

Question

I am trying to wrap my head around parameter sets. It seems fairly straight forward up until the point where you need to be able to use A or B, or both A & B. I need to essentially be able to say that out of two parameters, at least one must be provided.

This is an example of the code that I am currently using (without parameter sets), but this would allow for nothing but $c to be passed.

Function Test-Params
{
    Param
    (
        [string[]]
        $a,
        [string[]]
        $b,
        [Parameter(Mandatory=$true)]
        [string]
        $c
    )
}

Is there a way to handle this with parameter sets, or is it more appropriate to perform some form of validation within the function?

I would like for the following to be accepted:

Test-Params -a $arr_a -c "C:\test.txt"
Test-Params -b $arr_b -c "C:\test.txt"
Test-Params -a $arr_a -b $arr_b -c "C:\test.txt"

henrycarteruk · Accepted Answer · 2018-07-11 16:13:36Z

Define multiple Parameter Sets (blog on this) for each option you want to be accepted:

Function Test-Params {
    Param (
        [Parameter(ParameterSetName='AC', Mandatory=$True)]
        [Parameter(ParameterSetName='ABC', Mandatory=$True)]
        [string[]]$a,

        [Parameter(ParameterSetName='BC', Mandatory=$True)]
        [Parameter(ParameterSetName='ABC', Mandatory=$True)]
        [string[]]$b,

        [Parameter(ParameterSetName='AC', Mandatory=$True)]
        [Parameter(ParameterSetName='BC', Mandatory=$True)]
        [Parameter(ParameterSetName='ABC', Mandatory=$True)]
        [string]$c
    )

    $a
    $b
    $c
}

These will be accepted:

Test-Params -a ParamA -c ParamC
Test-Params -b ParamB -c ParamC
Test-Params -a ParamA -b ParamB -c ParamC

But if you try just A & B, it will use ParameterSetName='ABC' and prompt for C as this is also mandatory in that set.

C:\> Test-Params -a ParamA -b ParamB
cmdlet Test-Params at command pipeline position 1
Supply values for the following parameters:
c:

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