Question

A sad thing about PowerShell is that function and scriptblocks are dynamically scoped.

But there is another thing that surprised me is that variables behave as a copy-on-write within an inner scope.

$array=@("g")
function foo()
{
    $array += "h"
    Write-Host $array
}

& {
    $array +="s"
    Write-Host $array
}
foo

Write-Host $array

The output is:

g s
g h
g

Which makes dynamic scoping a little bit less painful. But how do I avoid the copy-on-write?

Answer 1

You can use scope modifiers or the *-Variable cmdlets.

The scope modifiers are:

• global used to access/modify at the outermost scope (eg. the interactive shell)
• script used on access/modify at the scope of the running script (.ps1 file). If not running a script then operates as global.

(For the -Scope parameter of the *-Variable cmdlets see the help.)

Eg. in your second example, to directly modify the global $array:

& {
  $global:array +="s"
  Write-Host $array
}

For more details see the help topic about_scopes.