ActiveDirectory change all UPN - powershell

Question

I have to change all UPN in my Active Directory. Some UPN are completely empty an some are filled.
Now I want to fill them all with their sAMAccountName.
My script looks like this:
# Import AD Module
Import-Module ActiveDirectory
# Import CSV into variable $userscsv
#$userscsv = import-csv C:\temp\rename\usernames.csv
$users = Import-Csv -Path C:\temp\rename\usernames.csv
# Loop through CSV and update users if the exist in CVS file
foreach ($user in $users) {
#Search in specified OU and Update existing attributes
Get-ADUser -Filter "sAMAccountName -eq '$($user.samaccountname)'"
Set-ADUser -userPrincipalName $($users.samaccountname)
}
I get an errorcode:
Get-ADUser : Der Suchfilter wurde nicht erkannt
Bei C:\TEMP\RENAME\User-Rename.ps1:13 Zeichen:12
+ Get-ADUser <<<< -Filter "sAMAccountName -eq '$($user.samaccountname)'"
+ CategoryInfo : NotSpecified: (:) [Get-ADUser], ADException
+ FullyQualifiedErrorId : Der Suchfilter wurde nicht erkannt,Microsoft.ActiveDirectory.Management.Commands.GetADUser
Does anyone have an idea?

Answer 1

I would not recommend setting the UPN to the SamAccountName. That's not how it's supposed to be.
If you must do it anyway, you can't use subexpressions in a filter. Assign the value to a variable and use that in the filter expression. You also need to pipe the user object into Set-ADUser to give the cmdlet something to work with:
foreach ($user in $users) {
$acct = $user.SamAccountName
Get-ADUser -Filter "sAMAccountName -eq '$acct'" |
Set-ADUser -userPrincipalName $acct
}