Get-Variable defined in a scriptblock from a psm function

Question

I have the following piece of code:

$x = 'xyz'
& {
    $y = 'abc'
    foo
}

The foo function is defined in the foo.psm1 module which is imported before the script block is started.

Inside the foo function, I call Get-Variable which shows me x but it doesn't show y. I tried playing with the -Scope parameter: Local, Script, Global, 0 - which is the local scope from what I understood from the docs, 1 - which is the parent scope.

How could I get the y variable inside the foo function?

I'm not looking for a solution such as passing it as an argument. I want something as Get-Variable but sadly it doesn't see it for some reason.

UP

Based on the comments received, probably more context is needed.

Say that foo receives a ScriptBlock which is using the $using: syntax.

$x = 'xyz'
& {
    $y = 'abc'
    foo -ScriptBlock {
        Write-Host $using:x
        Write-Host $using:y
    }
}

I'm 'mining' these variables as follows:

$usingAsts = $ScriptBlock.Ast.FindAll( { param($ast) $ast -is [System.Management.Automation.Language.UsingExpressionAst] }, $true) | ForEach-Object { $_ -as [System.Management.Automation.Language.UsingExpressionAst] }
foreach ($usingAst in $usingAsts) {
    $varAst = $usingAst.SubExpression -as [System.Management.Automation.Language.VariableExpressionAst]
    $var = Get-Variable -Name $varAst.VariablePath.UserPath -ErrorAction SilentlyContinue
}

This is how I'm using Get-Variable and in the case presented above, y cannot be found.

score 2 · Accepted Answer · answered Aug 01 '21 at 21:50

Modules run in their own scope domain (aka session state), which means they generally do not see the caller's variables - unless (a module-external) caller runs directly in the global scope.

For an overview of scopes in PowerShell, see the bottom section of this answer.

However, assuming that you define the function in your module as an advanced one, there is a way to access the caller's state, namely via the automatic $PSCmdlet variable.

Here's a simplified example, using a dynamic module created via the New-Module cmdlet:

# Create a dynamic module that defines function 'foo'
$null = New-Module {
  function foo {    
    # Make the function and advanced (cmdlet-like) one, via
    # [CmdletBinding()].
    [CmdletBinding()] param()
    # Access the value of variable $bar in the
    # (module-external) caller's scope.
    # To get the variable *object*, use:
    #    $PSCmdlet.SessionState.PSVariable.Get('bar')
    $PSCmdlet.GetVariableValue('bar')
  }
}

& {
  $bar = 'abc'
  foo
}

The above outputs verbatim abc, as desired.

Get-Variable defined in a scriptblock from a psm function

1 Answers1