Import difference in CSV to Azure sec group - powershell

Question

I want to compare all shared mailboxes in Exchange online with members in a Azure sec group and import the difference in the Azure sec group. I believe it fails somewhere in the last 3 rows. It is for a backup solution and I am not the creator of the code.
Get-EXORecipient -ResultSize unlimited -RecipientTypeDetails "SharedMailbox" | select PrimarySMTPAddress | Export-Csv "C:\Users\mnym\Downloads\Sharedmailboxes\sharedmailboxes.csv"
$GroupMembership = Get-AzureADGroupMember -ObjectId "group id" -top 10000 | Select-Object #{Name="PrimarySMTPAddress";Expression={$_.userprincipalname}} | Export-Csv "C:\Users\mnym\Downloads\Sharedmailboxes\Groupmembership.csv"
$File1 = Import-Csv -Path "C:\Users\mnym\Downloads\Sharedmailboxes\sharedmailboxes.csv"
$File2 = (Import-Csv -Path "C:\Users\mnym\Downloads\Sharedmailboxes\Groupmembership.csv").PrimarySMTPAddress
$File1 | where-object{$_.PrimarySMTPAddress -notin $File2} | Export-csv -path "C:\Users\mnym\Downloads\sharedmailboxes\difference.csv"
$Diff = Import-Csv -Path "C:\Users\mnym\Downloads\sharedmailboxes\difference.csv"
The file difference.csv is populated and formatted as
A
#TYPE Selected.System.Management.Automation.PSCustomObject
PrimarySmtpAddress
x#domain.com
$UserObjectId = Import-Csv -Path "C:\Users\mnym\Downloads\sharedmailboxes\difference.csv" | ForEach-Object {get-azureaduser -searchstring $_.PrimarySmtpAddress}
$Userobjectid | select objectid | export-csv -Path "C:\Users\mnym\Downloads\sharedmailboxes\userobjectid.csv"
The file userobjectid.csv is empty after above command :(
Import-Csv -Path "C:\Users\mnym\Downloads\sharedmailboxes\userobjectid.csv" | ForEach-Object {Add-AzureADGroupMember -ObjectId "group id" -Refobjectid $_.objectid}
I tried to import the difference.csv but I can't seam to get the Refobjectid to match the CSV, I get "Cannot bind argument to parameter 'RefObjectId' because it is null".

Answer 1

Don't use your file system as a variable registry - there's no need to write data to a CSV file only to read it straight back into memory :)
Your code could be as simple as:
# Define the target group id
$groupID = "group id"
# Start by creating a set of all email addresses that are already members of the security group
$securityGroupMembers = [System.Collections.Generic.HashSet[string]]::new([StringComparer]::OrdinalIgnoreCase)
Get-AzureADGroupMember -ObjectId $groupID -Top 10000 |ForEach-Object {
[void]$securityGroupMembers.Add($_.PrimarySMTPAddress)
}
# Then fetch the shared mailbox and check if they're already members of the group
Get-EXORecipient -ResultSize unlimited -RecipientTypeDetails "SharedMailbox" |ForEach-Object {
if(-not $securityGroupMembers.Contains($_.PrimarySMTPAddress)){
# Add shared mailbox to group
Add-AzureADGroupMember -ObjectId $groupID -Refobjectid $_.ObjectId
}
}