Mutually exclusive powershell parameters

You can use the parameter attribute to declare multiple parameter sets. You then simply assign parameters that are mutually exclusive to different parameter sets.

EDIT:

This is also documented in ‘about_Functions_Advanced_Parameters’, under the section “ParameterSetName Named Argument”. This is how different sets of parameters is handled with cmdlets like Get-Random (which has mutually exclusive parameters):

> get-random -input 4 -max 77
Get-Random : Parameter set cannot be resolved using the specified named parameters.
At line:1 char:11
+ get-random <<<<  -input 4 -max 77
    + CategoryInfo          : InvalidArgument: (:) [Get-Random], ParameterBindingException
    + FullyQualifiedErrorId : AmbiguousParameterSet,Microsoft.PowerShell.Commands.GetRandomCommand

Here’s an example of doing it in a function:

function exclusive_params() { 
    param( 
        [parameter(ParameterSetName="seta")]$one,
        [parameter(ParameterSetName="setb")]$two, 
        $three 
    )
    "one: $one"; "two: $two"; "three: $three" 
}

The parameters one and two are in different parameter sets, so they cannot be specified together:

> exclusive_params -one foo -two bar -three third
exclusive_params : Parameter set cannot be resolved using the specified named parameters.
At line:1 char:17
+ exclusive_params <<<<  -one foo -two bar -three third
    + CategoryInfo          : InvalidArgument: (:) [exclusive_params], ParameterBindingException
    + FullyQualifiedErrorId : AmbiguousParameterSet,exclusive_params

Which is the same error I got with Get-Random. But I can use the parameters independently:

> exclusive_params -one foo -three third
one: foo
two:
three: third

…or:

> exclusive_params -two bar -three third
one:
two: bar
three: third