update/modify ldap user attribute powershell - powershell

Question

My powershell script will update the ldap user attribute for non-Microsoft technology(Active Directory) and i faced some issue on it. This is my reference link for how to update non-Microsoft technology(Active Directory)
This is part of my powershell script
if($time -ne $null)
{
$eD = $time.AddDays(7)
write-host "The date after : "$eD
Set-ADUser xxxxx -AccountExpirationDate $eD
$a = New-Object "System.DirectoryServices.Protocols.DirectoryAttributeModification"
write-host $a
$a.Name = "String1"
write-host $a
$a.Operation = [System.DirectoryServices.Protocols.DirectoryAttributeOperation]::Add
write-host $a
#add values of the attribute
$a.Add("set")
write-host $a
$r.Modifications.Add($a)
$re = $ldapserver.SendRequest($r);
if ($re.ResultCode -ne [System.directoryServices.Protocols.ResultCode]::Success)
{
write-host "Failed!"
write-host ("ResultCode: " + $re.ResultCode)
write-host ("Message: " + $re.ErrorMessage)
}
}
Here are my script output
The date after 7 days : 14/1/2020 11:40:03 AM
0
set
You cannot call a method on a null-valued expression.
At D:\deployment\test_ck.ps1:94 char:25
+ $r.Modifications.Add($a)
+ ~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull
i cant figure out why $a is having a null value
This is what assigned to $r
$Domain='ou=test,ou=tes1,o=test2'
$fDomain ='(objectClass=User)'
$sDomain = New-Object System.DirectoryServices.Protocols.SearchRequest -ArgumentList $Domain,$fDomain,
$r = (new-object "System.DirectoryServices.Protocols.ModifyRequest")
$r = $sDomain

Answer 1

The simple PowerShell script below uses the Get-ADUser cmdlet from the ActiveDirectory PowerShell module to retrieve all the users in one OU and then iterate the users to set a couple of AD properties.
# Get all users in the Finance OU.
$FinanceUsers = Get-ADUser -Filter * -SearchBase "OU=Finance,OU=UserAccounts,DC=FABRIKAM,DC=COM"
# Iterate the users and update the department and title attributes in AD.
The example uses the Instance parameter of Set-ADUser to update each user in the OU. The parameter allows any modifications made to the ADUser object to go to the corresponding Active Directory object while only updating object properties that have changed.