Add 'Next Available AD Computer' to power-shell script - powershell

Question

Currently, I'm trying to add a function to my powershell script with the following goal:
On a computer that isn't added to the domain (yet), have it search a local AD server (Not azure) for the next available name based off the user's input.
I have tried and failed to use arrays in the past, and I want to use the Get-ADComputer cmdlet in this, but I'm not sure how to implement it.
$usrinput = Read-Host 'The current PC name is $pcname , would you like to rename it? (Y/N)'
if($usrinput -like "*Y*") {
Write-Output ""
$global:pcname = Read-Host "Please enter the desired PC Name"
Write-Output ""
$userinput = Read-Host "You've entered $pcname, is this correct? (Y/N)"
if($usrinput -like "*N*") {
GenName
#name of the parent function
}
Write-Output ""
The above code is part of a larger script that parses a computer name and assigns it to the correct OU in the end.
Our naming scheme works like this: BTS-ONE-LAP-000
So it is: Department - Location - Device Type - Device Count
The code will then take the first part "BTS-ONE" and parse it for the correct OU it should go to, and then assign it using the Add-Computer cmdlet. It will also rename the machine to whatever the user typed in ($pcname).
So, before it parses the name, I'd like it to search all current names in AD.
So, the user can type in: "BTS-ONE-LAP" and it will automatically find the next available Device Count, and add it to the name. So, it will automatically generate "BTS-ONE-LAP-041".
Added Note:
I've used Get-ADComputer -Filter 'Name -like "BTS-ONE-LAP-*"' | FT Name and the output is
Name
----
BTS-ONE-LAP-001
BTS-ONE-LAP-002
BTS-ONE-LAP-006
BTS-ONE-LAP-007
BTS-ONE-LAP-009
BTS-ONE-LAP-010
BTS-ONE-LAP-022
BTS-ONE-LAP-024
BTS-ONE-LAP-025
BTS-ONE-LAP-028
BTS-ONE-LAP-029
BTS-ONE-LAP-030
BTS-ONE-LAP-031
BTS-ONE-LAP-032
BTS-ONE-LAP-034
BTS-ONE-LAP-035
BTS-ONE-LAP-036
BTS-ONE-LAP-037
BTS-ONE-LAP-038
BTS-ONE-LAP-039
BTS-ONE-LAP-040
BTS-ONE-LAP-041
BTS-ONE-LAP-050
BTS-ONE-LAP-051
I don't know how to parse this so the code knows that BTS-ONE-LAP-003 is available (I'm terrible with arrays).

Answer 1

$list = (Get-ADComputer -Filter 'Name -like "BTS-ONE-LAP-*"' | Sort-Object Name[-1])
$i = 1
$found = $false
Foreach($Name in $list.Name)
{
while($i -eq [int]$Name.Split("-")[3].Split("-")[0])
{
$i++
}
}
$i
The above code will go through each name in the list, and will stop when it discovers say the 3rd computer in the set is NOT computer #3.
Example:
BTS-ONE-LAP-001 | $i = 1
BTS-ONE-LAP-002 | $i = 2
BTS-ONE-LAP-006 | $i = 3
It split BTS-ONE-LAP-006 to be 006, and convert it to an integer, making it 6.
Since 6 does not equal 3, we know that BTS-ONE-LAP-003 is available.

Answer 2

Another way could be to create a reusable function like below:
function Find-FirstAvailableNumber ([int[]]$Numbers, [int]$Start = 1) {
$Numbers | Sort-Object -Unique | ForEach-Object {
if ($Start -ne $_) { return $Start }
$Start++
}
# no gap found, return the next highest value
return $Start
}
# create an array of integer values taken from the computer names
# and use the helper function to find the first available number
$numbers = (Get-ADComputer -Filter 'Name -like "BTS-ONE-LAP-*"') |
ForEach-Object { [int](([regex]'(\d+$)').Match($_.Name).Groups[1].Value) }
# find the first available number or the next highest if there was no gap
$newNumber = Find-FirstAvailableNumber $numbers
# create the new computername using that number, formatted with leading zero's
$newComputerName = 'BTS-ONE-LAP-{0:000}' -f $newNumber
Using your example list, $newComputerName would become BTS-ONE-LAP-003
Note that not everything a user might type in with Read-Host is a valid computer name. You should add some checks to see if the proposed name is acceptable or skip the proposed name alltogehter, since all your machines are named 'BTS-ONE-LAP-XXX'.
See Naming conventions in Active Directory for computers, domains, sites, and OUs