ForEach-Object on empty array returns $null

Question

Why does the expression @() | ForEach-Object { $_ } evaluate to $null? I would expect it to return an empty array.

Is there a short expression to coalesce $null to an empty array for PowerShell 5? In PowerShell 7 I can do $array ?? @().

Simply wrap your pipeline in another array-subexpression: $alwaysArray = @(@() | ForEach-Object { $_ }) — Mathias R. Jessen
– Mathias R. Jessen, Commented Jan 26, 2022 at 13:02
Consider what your example does; it passes nothing to the pipeline. Foreach-Object has no objects to iterate over. — Robin
– Robin, Commented Jan 26, 2022 at 13:21
Thanks for answering the second question. But still I am wondering why PowerShell behaves the way it does. In every other language I know, mapping an empty list still results in an empty list. — Börg
– Börg, Commented Jan 26, 2022 at 13:41
Or use the unary comma operator to wrap the emty array in a new single-element array. Upon return, PowerShell will unwrap the surrounding array leaving you with the inner (empty) array. $a = ,(@() | ForEach-Object { $_ }). You can also do that on $null: $a = ,$null; $a.GetType() --> Object[] — Theo
– Theo, Commented Jan 26, 2022 at 14:17
Check this: @() |ForEach-Object { $_ } |ForEach-Object { 'Test' }. In other words, it doesn't return a $Null, it returns a System.Management.Automation.Internal.AutomationNull which it changed in a $Null when it is assigned to a variable. See: Everything you wanted to know about $null. — iRon
– iRon, Commented Feb 3, 2022 at 9:07

Tal Folkman · Accepted Answer · 2022-01-26 13:14:34Z

2

try wrap your command with an array operator @.

so it will be -

$array = @(@() | ForEach-Object { $_ })

answered Jan 26, 2022 at 13:14

Tal Folkman

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2 Comments

Börg Over a year ago

This only works because ForEach-Object returns a void object. If it would actually return $null, $array would have 1 element. Is there a similar construct that also works for $null?

iRon Over a year ago

I downvoted this answer because it doesn't answer the question "Why does the expression @() | ForEach-Object { $_ } evaluate to $null?". In fact, it returns an Emprty Null, a System.Management.Automation.Internal.AutomationNull which will changed in a $Null only when it is assigned. Check this: @() |ForEach-Object { $_ } |ForEach-Object { 'Test' }.

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