Checking if PC exists in AD, and if not creating it

Question

Need to write a script to take an input file (text) list of names, check if it exists in AD, and create new computers.

The requirements are as follows -

Computer names are based on the users name (input from file)
Names must be 15 characters (for name resolution)
if the truncated name doesnt exist, create a computer object in specific OU with the truncated name.
If the truncated name does exist, append -# and test to see if it exists until it finds one that doesnt, then create new computer object with that name.

At the end I will need to output the results to an array but I haven't started adding that yet since this doesn't work.

So I finally got the "else" part but the if part at the beginning does not work.

$users = get-content C:\scriptdata\VMS.txt
$OU = ************
foreach ($user in $users) 
{
    $cleanname = if ($user.Length -gt 15) { $user.Substring(0, 15) } else { $user }
    $exist = (get-adcomputer $cleanname) -eq $null
    if ((get-adcomputer $cleanname) -like "get-adcomputer : Cannot find an object with identity")
        {
            New-ADComputer -Name $cleanname -Path "$OU" -SAMAccountName $cleanname -confirm
        }
    else
        {
            $count=0
            DO{
            $count++
            $cleanname13 = if ($user.Length -gt 13) { $user.Substring(0, 13) } else { $cleanname }
            $cleannamedash = $cleanname13 + '-' + "$count"
        }
            UNTIL ((get-adcomputer $cleannamedash | out-null) -eq $null)
            New-ADComputer -Name $cleannamedash -Path "$OU" -SAMAccountName $cleannamedash -confirm
        }
}

currently works for -# but not for those that dont exist at all.

Theo · Accepted Answer · 2019-08-17 08:30:02Z

Have a look at Naming conventions in Active Directory for computers, domains, sites, and OUs.
You'll find that there is more to a valid computer name than just the length.

Mind that the New-ADComputer cmdlet creates a new computer object, but does not join a computer to a domain.

Something like this should work (untested)

$computers = Get-Content C:\scriptdata\VMS.txt | Where-Object { $_ -match '\S'}
$OU = ************

foreach ($name in $computers) {
    $newName = ($name -creplace '[\\/:*?"<>|.]','').Substring(0, 15)
    try {
        $computer = Get-ADComputer -Filter "Name -eq '$newName'" -PassThru -ErrorAction Stop
    }
    catch {
        $computer = $null
    }
    if ($computer) {
        # a computer with that name already exists, create a new name by adding a dash and two digit number
        $count = 0
        $name12 = $newName.Substring(0, 12)   # we're going to add three characters
        # get an array of computernames that are like the one you want to create
        $existingComputers = Get-ADComputer -Filter "Name -like '$name12-*'" | Select-Object -ExpandProperty Name
        do {
            $newName = '{0}-{1:00}' -f $name12, ++$count
        }
        until ($existingComputers -notcontains $newName -or $count -gt 99)

        if ($count -gt 99) {
            $newName = '{0}-XX' -f $name12
            throw "Cannot create computer $newName because all index numbers 00..99 are taken.."
        }
    }


    # use splatting, because New-ADComputer has MANY parameters
    $props = @{
        'Name'           = $newName
        'Path'           = $OU
        'SamAccountName' = $newName
        'Enabled'        = $true
        'Confirm'        = $true
    }

    Write-Host "Creating computer '$newName'"
    New-ADComputer @props
}

Gabriel Luci · Accepted Answer · 2019-08-16 15:11:04Z

I assume you mean that this is the line that's not working:

if ((get-adcomputer $cleanname) -like "get-adcomputer : Cannot find an object with identity")

And even this doesn't work:

$exist = (get-adcomputer $cleanname) -eq $null

The reason is the same in both cases: If the computer doesn't exist, then Get-ADComputer throws an exception and the comparison is never done.

There is a good article about this here, but in short, the solution is to catch the exception. For you, it would look something like this:

try {
    $computer = Get-ADComputer $cleanname
    # If we get here, we know it exists
    # You can put your loop here and just keep looping until Get-ADComputer throws an exception
}
catch [Microsoft.ActiveDirectory.Management.ADIdentityNotFoundException]
{
    # Whatever you last tried doesn't exist. Create it here.
}

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