Powershell function to detect UPN for the currently logged user

Get-CurrentUPN.ps1

Function Get-CurrentUPN
{
	$UserPrincipalName = $NULL
	#
	$UPNList = @()
	$UPN = $Env:USERNAME
	if($UPN -eq $NULL){
		$UPN = (whoami)
		if($UPN -ne $NULL){
			$UPN = $UPN.split("\")[-1]
		}else{
			$Proc = Get-CimInstance Win32_Process -Filter "name = 'powershell.exe'"
			if($proc.GetType().BaseType.name -eq "Array"){
				foreach($process in $proc){
					$UPNList += Invoke-CimMethod -InputObject $process -MethodName GetOwner | select -ExpandProperty User
				}
				$UPN = $UPNList | select -first 1
			}else{
				$UPN = Invoke-CimMethod -InputObject $process -MethodName GetOwner | select -ExpandProperty User
			}
		}
	}
	
	#Find UPN
	$strFilter = "(&(objectCategory=User)(SAMAccountName=$($UPN)))"
	$objDomain = New-Object System.DirectoryServices.DirectoryEntry
	$objSearcher = New-Object System.DirectoryServices.DirectorySearcher
	$objSearcher.SearchRoot = $objDomain
	$objSearcher.PageSize = 1
	$objSearcher.Filter = $strFilter
	$objSearcher.SearchScope = "Subtree"
	$objSearcher.PropertiesToLoad.Add("userprincipalname") | Out-Null
	$colResults = $objSearcher.FindAll()
	[string]$UserPrincipalName = $colResults[0].Properties.userprincipalname
	Return $UserPrincipalName
}