How to pass $_ ($PSItem) in a ScriptBlock

Question

I\'m basically building my own parallel foreach pipeline function, using runspaces.

My problem is: I call my function like this:

somePipeline | MyNew         


        

Answer 1

The key is to define $_ as a variable that your script block can see, via a call to Set-Variable.

Here's a simple example:

function MyNewForeachFunction {
  [CmdletBinding()]
  param(
    [Parameter(Mandatory)]
    [scriptblock] $ScriptBlock
    ,
    [Parameter(ValueFromPipeline)]
    $InputObject
  )

  process {
    $PSInstance = [powershell]::Create()

    # Add a call to define $_ based on the current pipeline input object
    $null = $PSInstance.
      AddCommand('Set-Variable').
        AddParameter('Name', '_').
        AddParameter('Value', $InputObject).
      AddScript($ScriptBlock)

    $PSInstance.Invoke()
  }

}

# Invoke with sample values.
1, (Get-Date) | MyNewForeachFunction { "[$_]" }

The above yields something like:

[1]
[10/26/2018 00:17:37]