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:\DEPARTMENTS\CBR\SHARE\Target'
    Destination = 'E:\DEPARTMENTS\CBR\SHARE\Target 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.

Answer 2

Here's one way to approach passing named parameters:

function Copy-FilesHC 
{
  param ($Source,$Destination,$Structure)
  "Source is $Source"
  "Desintation is $Destination"
  "Structure is $Structure"
  }


$CopyParams = @{
    Source      = 'E:\DEPARTMENTS\CBR\SHARE\Target'
    Destination = "'E:\DEPARTMENTS\CBR\SHARE\Target 2'" #Nested quotes required due to embedded space in value.
    Structure   = 'yyyy-MM-dd'
}

$SB = [scriptblock]::Create(".{${Function:Copy-FilesHC}} $(&{$args}@CopyParams)")

Invoke-Command -Credential $Cred -ComputerName 'SERVER' -ScriptBlock $SB

Basically, you create a new script block from your invoked script, with the parameters splatted to that from the hash table. Everything is already in the script block with the values expanded, so there's no argument list to pass.