How to pass a [switch] parameter to a PowerShell script from C#?

Question

I have this powershell script named testSwitch.ps1:

param(
    [switch] $s
)

Return 's= ' + $s

When I invoke this script directly in PowerShell like this:

.\testSwitch.ps1 -s

The output is

s= True

And it outputs False when the switch is missing. But when I try to invoke the same script with this C# code:

Command command = new Command(@"testSwitch.ps1");

command.Parameters.Add(new CommandParameter("s"));

RunspaceConfiguration runspaceConfiguration = RunspaceConfiguration.Create();
using (Runspace runspace = RunspaceFactory.CreateRunspace(runspaceConfiguration))
{
    runspace.Open();
    Pipeline pipeline = runspace.CreatePipeline();
    pipeline.Commands.Add(command);

    IEnumerable<PSObject> psresults = new List<PSObject>();
    psresults = pipeline.Invoke();
    Console.WriteLine(psresults.ToArray()[0].ToString());
}

the output is:

s= False

It seems that the CommandParameter always interprets switch parameters as false, unlike the PowerShell command-line interpreter. The frustrating thing is that this causes the script to see a value of false for the [switch] parameter without throwing any exceptions about not specifying a value. As opposed to a [bool] parameter, which will throw an exception if you do not provide a value in the CommandParameter constructor.

Matt Faus · Accepted Answer · 2012-04-24 18:43:11Z

5

Strangely enough, you must specify true as the parameter value, like so:

command.Parameters.Add(new CommandParameter("s", true));

Furthermore, specifying false also works as expected:

command.Parameters.Add(new CommandParameter("s", false));

Returns

s= False

So, I guess [switch] parameters should be treated exactly like [bool] parameters when invoking from C#!

answered Apr 24, 2012 at 18:43

Matt Faus

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