Get-UniqueSamAccountNames

Get-UniqueSamAccountNames.ps1

$Items = Import-Csv '.\data.csv'

$Items | ForEach-Object {
    #Init our flag for a unique username
    $Unique = $false
    #Init our target SamAccountName
    $Target_SamAccountName = $_.SamAccountName
    #Init Regex pattern
    $Pattern = "^$Target_SamAccountName\d*"
    #Get all existing accounts that have the same SamAccountName regardless of numeric suffix
    $ExistingItems = @(Get-ADUser -Filter "SamAccountName -like '$Target_SamAccountName*'" | Where-Object {$_.SamAccountName -match $Pattern} | Select-Object -ExpandProperty SamAccountName)
    
    if ($ExistingItems -notcontains $Target_SamAccountName) { #Found unique on first try
        $Unique = $true
    }
    else { #Have to search for next available unique numeric suffix
        #Init our numeric suffix
        $Numeric = 1
        while (-not $Unique) {
            if($ExistingItems -notcontains "$Target_SamAccountName$Numeric") { #Found next available numeric suffix
                $Unique = $true
                $Target_SamAccountName = "$Target_SamAccountName$Numeric"
            }
            else { #Try next
                $Numeric++
            }
        }
    }
    
    # Log the info/create an account, etc...
    Write-Host $Target_SamAccountName
}