Powershell array scope; why is my array empty?

Question

I want to have an array and add elements to it from different functions in my script. My example below illustrates where I might be misunderstanding something regarding scope. My understanding currently is that if an array is defined outside the function, and then elements are added inside the function, those elements should be available outside the function.

Function ListRunningServices
{
    $services+= Get-Service | ?{$_.Status -eq "Running"} | sort Name | select Name;
}

$services = @();
ListRunningServices;
$services;

What am I missing here? Perhaps my style is completely wrong.

Answer 1

You can solve this with global variables, but using globals is genereally considered bad practice. If you use a generic collection type, like arraylist, instead of an array then you have an add() method that will update the collection in a parent scope without needing to explicitly scope it in the function:

Function ListRunningServices
{
    Get-Service | ?{$_.Status -eq "Running"} | sort Name | select Name |
     ForEach-Object {$services.add($_)}
}

$services = New-Object collections.arraylist
ListRunningServices
$services