Powershell - Strange variable value return

Question

I have a (for me) strange result with a script. This is a summary of my script which returns the same result:

cls
$Init          = "AFFAIRES"
$ListeGroupes  = @() 
$NomGrScan     = "AFFAIRES"
$Grp0          = New-Object psobject
$Grp0          | Add-Member -Name "Nom"  -MemberType NoteProperty -value $Init
$Grp0          | Add-Member -Name "Scan" -MemberType NoteProperty -value "N"
$ListeGroupes += $Grp0 
$LGroupes1     = @()
$LGroupes1    += $ListeGroupes
write-host "Grp0 : $($Grp0.Nom) - $($Grp0.scan)"
write-host "ListeGroupes : $($ListeGroupes.Nom) - $($ListeGroupes.scan)"
write-host "LGroupes1 : $($LGroupes1.Nom) - $($LGroupes1.scan)"
($LGroupes1 | where {$_.nom -eq "$NomGrScan"}).scan = "O"
write-host "============================================="
write-host "Grp0 : $($Grp0.Nom) - $($Grp0.scan)"
write-host "ListeGroupes : $($ListeGroupes.Nom) - $($ListeGroupes.scan)"
write-host "LGroupes1 : $($LGroupes1.Nom) - $($LGroupes1.scan)"

When I run it on my computer I get:

Grp0 : AFFAIRES - N
ListeGroupes : AFFAIRES - N
LGroupes1 : AFFAIRES - N
=============================================
Grp0 : AFFAIRES - O
ListeGroupes : AFFAIRES - O
LGroupes1 : AFFAIRES - O

On line 15 of the script I only change the value of $LGroupe1. Why does it also change the values of $ListeGroupe and $Grp0?

I don't understand why I don't get:

Grp0 : AFFAIRES - N
ListeGroupes : AFFAIRES - N
LGroupes1 : AFFAIRES - N
=============================================
Grp0 : AFFAIRES - N
ListeGroupes : AFFAIRES - N
LGroupes1 : AFFAIRES - O

mhhollomon · Accepted Answer · 2019-10-29 16:41:01Z

1

In Powershell, objects (like the value in $Grp0) are treated as references. So, assigning a varible to an existing object gets you - not a new object - but another reference to the same object.

$a = New-Object PSObject -Property @{ prop1='a' ; prop2='b' }
$b = $a

$b points to the same object as $a. Changes to one affect the other.

One possible way to get around this is to use the Copy() method on PSObject.

$a = New-Object PSObject -Property @{ prop1='a' ; prop2='b' }
$b = $a.PSObject.Copy()

Now, $a and $b point to different objects and changes to one will not affect the other.

Note that Copy() only does a shallow copy.

edited Oct 29, 2019 at 16:41

answered Oct 28, 2019 at 11:31

mhhollomon

9937 silver badges16 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Info VSA Over a year ago

Thank you so much for your help. Now I understand better.

Info VSA · Accepted Answer · 2019-10-29 16:08:22Z

0

I came to try your code :

$a = New-Object PSObject -Property @{ prop1='a' ; prop2='b' }
$b = $a.Copy()

and i have this (sorry it's in french) :

Échec lors de l’appel de la méthode, car [System.Management.Automation.PSCustomObject] ne contient pas de méthode nommée « Copy ».
_Failed to call the method, because [System.Management.Automation.PSCustomObject] does not contain a method named "Copy"_
Au caractère Ligne:2 : 1
+ $b = $a.Copy()
+ ~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation : (Copy:String) [], RuntimeException
    + FullyQualifiedErrorId : MethodNotFound

Where is my mistake ? thank you

answered Oct 29, 2019 at 16:08

Info VSA

1

1 Comment

mhhollomon Over a year ago

Ooop! forgot the important qualifier on the Copy(). That line should be $b = $a.PSObject.Copy() Answer corrected.

Collectives™ on Stack Overflow

Powershell - Strange variable value return

2 Answers 2

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related