PowerShell script to count members of multiple groups without duplicates - powershell

Question

I need to write a PowerShell script that will count the users in 4 groups:
group1
group2
group3
group4
The script needs to skip duplicates if a user is in multiple groups.
Previously I was using the following script to count users in each group separately, but it is including duplicates and I need the accurate count of users from all groups.
$ADInfo = Get-ADGroup -Identity '<groupname>' -Properties Members
$ADInfo.Members |Where-Object {(Get-ADUser $_ -Properties extensionAttribute4).extensionAttribute4 -eq 'o365_facstaff'} |Select -Unique | Measure-Object

Answer 1

You could adjust this to send a collection down the pipeline. Something like the below should work:
$Groups = 'Group1','Group2','Group3','Group4'
$Groups |
Get-ADGroup -Properties Member |
Where-Object {(Get-ADUser $_ -Properties extensionAttribute4).extensionAttribute4 -eq 'o365_facstaff'} |
Select-Object -Unique |
Measure-Object
However, I would probably go about it a little different:
$Groups = 'Group1','Group2','Group3','Group4'
$Groups |
Get-ADGroupMember |
Where-Object{ $_.objectCLass -eq 'user'} |
Get-ADUser -Properties extensionAttribute4 |
Where-Object{ $_.extensionAttribute4 -eq 'o365_facstaff' } |
Select-Object -Unique |
Measure-Object
Note: In your original code the Get-ADUser command might error if you send it a group since groups can be members of other groups. That's why there's an extra Where{} clause in the above example to only looking for objectClass 'user'.
If you care to mess with the group Distinguished Names you could also try using an LDAP filter:
$Groups = #(
'Group1_DN'
'Group2_DN'
'Group3_DN'
'Group4_DN'
)
$LDAPFilter = "(&(extensionAttribute4=o365_facstaff)(|(memberOf={0})(memberOf={1})(memberOf={2})(memberOf={3})))" -f $Groups
Get-ADUser -LDAPFilter $LDAPFilter |
Select-Object -Unique |
Measure-Object
This will return all users where extensionAttribute4 is 'o365_facstaff' that are members of any 4 groups. Then it will run through Select -Unique & Measure-Object as before.
Note: Performance probably isn't a big factor in this case. However, it's always a best practice to move filtering left in the command as opposed to post filtering with a Where{} clause or other secondary processing. In this case, leveraging the cmdlet's built-in filtering parameters.