Using PowerShell to generate a unique username in AD - powershell

Question

I'm writing a script to be used by help desk staff to quickly (and accurately) create AD user accounts by inputting basic employee information. We use portions of a persons name in order to create the samAccountName. Which I've achieve by the following.
$GivenName = "Joe"
$Surname = "Smith"
$SamAccountName = $Surname.substring(0, [System.Math]::Min(5, $Surname.Length)) + $GivenName.Substring(0,1)
This works great as long as there isn't already a "Joe Smith" (or John or Jennifer Smithers, etc). The solution would be to add a number to the end. When manually creating accounts the help desk would search AD look at what number suffix to use if necessary. I'm trying to figure out how PowerShell can do that for us. I've gone through several ideas with help from what I've found online but so far I've been unsuccessful.
My first thought was to do something like this.
$SamSuffix = 2
If ((Get-ADUser -LDAPFilter "(SamAccountName=$samAccountName)")-eq $Null)
{
"$SamAccountName does not exist in AD" #out result for testing.
}
Else{
do
{
Get-ADUser -LDAPFilter "(SamAccountName=$SamAccountName + $SamSuffix++)"
}
until (Get-ADUser -LDAPFilter "(SamAccountName=$SamAccountName + $SamSuffix)")-eq $Null)
}
This obviously doesn't work. Even if it did I don't know how I'd get to the 'next step' to create the account.
I also tried pulling the existing names into a list
$SamExist = (Get-ADUser -LDAPFilter "(SamAccountName=$SamAccountName*)" | Select SamAccountName)
do {$SamAccountName + $SamSuffix++}
until ($SamExist -notcontains $SamAccountName -or $SamAccountName + $SamSuffix)
This also doesn't work but if it did I can see that it would automatically add the suffix even if it wasn't needed.

Answer 1

You approach where you get all the existing matches first would be where I would start. Lets assume $SamAccountName is smithj
$existingAccounts = Get-ADUser -Filter "samaccountname -like '$SamAccountName*'" -ErrorAction SilentlyContinue | Select-Object -ExpandProperty samaccountname
So $existingaccounts that have a samaccountname's starting with smithj. If there are not any then $existingAccounts would be null and we can test for that.
if($existingAccounts){
# Figure out what the suffix will be
$highestValue = $existingAccounts -replace "^$SamAccountName" |
ForEach-Object{[int]$_} |
Measure-Object -Maximum |
Select-Object -ExpandProperty Maximum
} else {
# Create the user as normal.
}
Pretending there are some accounts that exist we trim the leading characters from the samaccountname, convert the remaining to an integer and select the highest from that. So $highestValue is the last number used in a conflicting account.
Add one to that and you have a guaranteed username you can create assuming nothing changes in those moments i.e. two users making to smithj accounts.
If you are looking to fill gaps where a user might have left and you want to use the next available after 1 then you could do this.
$existingAccounts = "smithj1", "smithj5", "smithj10", "smithj2", "smithj3"
# Figure out what the next unused suffix will be
$existingSuffixes = $existingAccounts -replace "^$SamAccountName" | ForEach-Object{[int]$_}
# Once again determine the maximum one in use
$highestValue = $existingSuffixes | Measure-Object -Maximum | Select-Object -ExpandProperty Maximum
# Find the first gap between 1 and the max suffix
$nextAvailableSuffix = 1..($highestValue + 1) | Where-Object{$existingSuffixes -notcontains $_} | Sort-Object desc | Select -First 1
$nextAvailableSuffix would contain 4 using the above example. We add 1 to highest value in case the only other one is 2 so that way there will only be an answer to $nextAvailableSuffix