Null troubles with PowerShell AD script for creating new users-CodePudding

Been smooth sailing with creating users for my domain, now I'm trying to set the uidNumber based on what the last 4 digits of the generated objectSid. Might be a simple solution but hoping for some help.

The rest of the code runs fine until we get to the '$last4' variable so I snipped to make it shorter, but if putting the whole script helps, happy to do so.

Import-Module ActiveDirectory

$firstname = Read-Host -Prompt "Please enter the first name"
$lastname = Read-Host -Prompt "Please enter the last name"

$location = Read-Host -Prompt "Please enter user location (LA/NY)"
$path = "OU=Users,OU=$location,OU=GS,DC=random,DC=com"

New-ADUser `
   -snip

Add-ADGroupMember `
    -Identity "$snip" -Members $username

$user = Get-ADUser -Identity $username

$objectSid = $user.objectSid

$last4DigitsOfObjectSid = $objectSid.Substring($objectSid.Length - 4)
$newUidNumber = "71$last4DigitsOfObjectSid"

Set-ADUser -Identity $username -Replace @{'uidNumber'=$newUidNumber}

Error

You cannot call a method on a null-valued expression. At C:\Users\Administrator\Desktop\newtry.ps1:31 char:1
$last4DigitsOfObjectSid = $objectSid.Substring($objectSid.Length - 4)
CategoryInfo : InvalidOperation: (:) [], RuntimeException FullyQualifiedErrorId : InvokeMethodOnNull

CodePudding user response：

objectSid is not an attribute that Get-ADUser returns by default, the attribute you're looking for is just SID. $objectSid in your snippet is actually null, hence the error you're having.

Also, Substring is a String method and SID and objectSid are instances of SecurityIdentifier. This class does not have a Substring method. You would need to refer to the .Value property:

$sid = $user.SID
$last4DigitsOfObjectSid = $sid.Value.Substring($sid.Value.Length - 4)

A much easier way of getting the last 4 digits would be with -replace which will coerce the SecurityIdentifier to a string before replacing:

$sid = $user.SID
$last4DigitsOfObjectSid = $sid -replace '. (?=.{4}$)'

Or using -split which would also work for SIDs having less than 4 digits:

$last4DigitsOfObjectSid = ($sid -split '-')[-1]