How do you access underlying PowerShell runspace from C# Cmdlet?

Question

I am building some PowerShell cmdlets using the C#/.NET APIs and have a cmdlet that needs access to all the currently imported modules. If I run Get-Module in the terminal I can see 10+ modules loaded, but when my cmdlet runs:

using(var ps = PowerShell.Create(RunspaceMode.Current))
{
    var modules = ps.AddCommand("Get-Module").Invoke<PSModuleInfo[]>();
    /// ...
}

modules here is empty. Its almost like a scoping problem, but I thought RunspaceMode.Current would allow you to access that underlying runspace that was opened with you first open the pwsh shell.

I must be missing something or misunderstanding exactly how runspaces work.

"a cmdlet that needs access to all the currently imported modules" sounds like a code smell... what is it that you're trying to accomplish? — Mathias R. Jessen
– Mathias R. Jessen, Commented Nov 19, 2020 at 20:59
Well tbh this isn't exactly the code I am dealing with, just a basic example. However, my code does some dynamic PS module proxy generation and after my cmdlet is "done" I need it to clean up after itself. So I am trying to call "Remove-Module" on these dynamic modules and nothing seems to happen when that is ran from inside the cmdlet. It appears to be the same issue that "Get-Module" has though and its a simpler example which is why I used that in my question. — Matt Hintzke
– Matt Hintzke, Commented Nov 19, 2020 at 21:04
If I wrote my Cmdlet in PS directly this would all work, so I guess I don't understand why this doesn't work as soon as you try it in C#. — Matt Hintzke
– Matt Hintzke, Commented Nov 19, 2020 at 21:06

Mathias R. Jessen · Accepted Answer · 2020-11-19 22:02:34Z

1

You're not supposed to mess around with the invoking runspace directly from inside a cmdlet - it's already busy executing your cmdlet. You also cannot invoke a PSCmdlet directly from another, for the same reason.

Instead, you'll want to use PSCmdlet.InvokeCommand.InvokeScript() to have the runtime execute a script for you (just like if you had a Get-Module statement in a PowerShell function):

[Cmdlet(VerbsCommon.Get, "ModuleProxy")]
public class GetModuleProxyCommand : PSCmdlet
{
    // ...

    protected override void EndProcessing()
    {
        foreach(var module in InvokeCommand.InvokeScript("Get-Module"))
        {
            WriteObject(module);
        }
    }
}

That being said, if what you're doing affects the environment in a way that requires you to execute Remove-Module or clean stuff up in the callers context, you're probably much better off doing your work in a separate runspace anyway :)

answered Nov 19, 2020 at 22:02

Mathias R. Jessen

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3 Comments

Matt Hintzke Over a year ago

Ok thanks that at least clears up "why" it doesn't seem to a let you do this. I am doing some very non-traditional things here with PS so its not as straightforward as one might think. These "extra" proxies are transient and meant to only act as a facade to provide caching of connection/auth. It's a long story, haha. But I will try to do this another way similar to what you stated. Thanks

Mathias R. Jessen Over a year ago

@MattHintzke That doesn't sound especially non-traditional or weird at all - in fact it sounds a lot like JEA :)

Matt Hintzke Over a year ago

Haha, ok well that is good. Since you seem like a PowerShell guru you might be interested in seeing what we are building. skykick.com/manage. Aims to help reduce the cognitive load of IT management as SaaS, IaaS, and PaaS becomes more complex.

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