Import functions in remote sessions

Want to use a custom function inside a PSSession or BackgroundJob, use this one-liner to do all the heavy lifting.

Invoke-Expression ${Using:Function:<functionname>}.Ast.Extent.Text

Here’s a simple example:

function Invoke-HelloWorld {
    Write-Warning "Hello World"
}

$ScriptBlock = {
    Invoke-Expression ${Using:Function:Invoke-HelloWorld}.Ast.Extent.Text
    Invoke-HelloWorld
}

Start-Job -ScriptBlock $ScriptBlock | Receive-Job -Wait -AutoRemoveJob

How does it work? Let’s break it down:

${} : Curly braces in PowerShell variable names allow for arbitrary characters in the name of the variable.
$Using:<VariableName> : Using Local variables in remote session.
$Function:<FunctionName> : Provides access to the functions defined in Windows PowerShell.

We are basically doing some kind of inception, pulling the function definition from our local session.

But why ${}.Ast.Extent.Text? my head hurts…

We dont want the scriptblock inside the function. We want the entire function definition as a string.

Hope this helps!

And dont forget to msg me on Twitter (@mkellerman), love getting your feedback!

References:

• About Remote Variables: Link

• Function Provider: Link