argument passing - PowerShell Splatting the Argumentlist on Invoke-Command

Question

How is it possible to use the parameters collected in a hash table for use with ArgumentList on Invoke-Command?

$CopyParams = @{
    Source      = 'E:DEPARTMENTSCBRSHARETarget'
    Destination = 'E:DEPARTMENTSCBRSHARETarget 2'
    Structure   = 'yyyy-MM-dd'
}
Invoke-Command -Credential $Cred -ComputerName 'SERVER' -ScriptBlock ${Function:Copy-FilesHC} -ArgumentList @CopyParams

Whatever I try, it's always complaining about the 'Source':

Cannot validate argument on parameter 'Source'. The "Test-Path $_" validation script for the argument with
 value "System.Collections.Hashtable" did not return true. Determine why the validation script failed

This blog talks about a similar problem, but I can't get it to work.

The same is true for a simple Copy-Item within Invoke-Command, example:

Invoke-Command -Credential $Cred -ComputerName 'SERVER' -ScriptBlock {Copy-Item} -ArgumentList @CopyParams

Invoke-Command : Missing an argument for parameter 'ArgumentList'. Specify a parameter of type 'System.Obj
ect[]' and try again.
At line:11 char:89
+ ... ck {Copy-Item} -ArgumentList @CopyParams

Thank you for your help.

Answer 1

One-liner, to convert a remote script to accept named parameters from a hash.

Given a scriptblock which you wish to call like this:

$Options = @{
    Parameter1 = "foo"
    Parameter2 = "bar"
}

Invoke-Command -ComputerName REMOTESERVER -ArgumentList $Options -ScriptBlock {
    param(
        $Parameter1,
        $Parameter2
    )
    #Script goes here, this is just a sample
    "ComputerName: $ENV:COMPUTERNAME"
    "Parameter1: $Parameter1"
    "Parameter2: $Parameter2"
} 

You can convert it like so

Invoke-Command -Computername REMOTESERVER -ArgumentList $Options -ScriptBlock {param($Options)&{
    param(
        $Parameter1,
        $Parameter2
    )
    #Script goes here, this is just a sample
    "ComputerName: $ENV:COMPUTERNAME"
    "Parameter1: $Parameter1"
    "Parameter2: $Parameter2"
} @Options}

What's going on? Essentially we've wrapped the original script block like so:

{param($Options)& <# Original script block (including {} braces)#> @options }

This makes the original script block an anonymous function, and creates the outer script block which has a parameter $Options, which does nothing but call the inner script block, passing @options to splat the hash.