Issue adding to a Substring if a dsquery finds the same sAMAccountName - windows

Question

I am editing a Powershell script that a colleague created before they left which I assume was created on an older version of Powershell/Activedirectoy. It is to create an AD account but I'm having an issue checking if a username already exists then carrying out an action if it does.
$UsernameInteger = 1
$sAMAccountName = $sn+$givenName.substring(0,$UsernameInteger)
# Check to see if the username is available in Active Directory
do
{
if (dsquery user -samid $sAMAccountName)
{
$CreateUser = $False
$UsernameInteger++
$Username = $sn+$givenName.substring(0,$UsernameInteger)
}
Else
{
$CreateUser = $True
}
}
Until ($CreateUser -eq $True)
When I run this code with an account with the same name I get the following error:
Exception calling "Substring" with "2" argument(s): "Index and length must refer to a location within the string.
Parameter name: length"
At C:\AD Account Creation.ps1:43 char:5
+ $Username = $sn+$givenName.substring(0,$UsernameInteger)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : ArgumentOutOfRangeException
What I want is when the $createuser = $false then it will add the next letter of their $givenName to the $username and keep doing this until an account with the same $sAMAccountName is not found and the account can be created.
How would I go about doing this?

Answer 1

You've incremented the counter to a value bigger than the length of the $givenName string. You need to change the increment logic to something like:
if ($UsernameInteger -le $givenName.length) {
$UsernameInteger++
}
This won't help if the username you pass in already exists in its entirety though, so you'll also need to handle that scenario