Function parameter always empty why?

Question

Can someone tell me, why this function call does not work and why the argument is always empty ?

function check([string]$input){
  Write-Host $input                             #empty line
  $count = $input.Length                        #always 0
  $test = ([ADSI]::Exists('WinNT://./'+$input)) #exception (empty string) 
  return $test
}

check 'test'

Trying to get the info if an user or usergroup exists..

Best regards

Answer 1

$input is an automatic variable.

https://technet.microsoft.com/ru-ru/library/hh847768.aspx

$Input

Contains an enumerator that enumerates all input that is passed to a function. The $input variable is available only to functions and script blocks (which are unnamed functions). In the Process block of a function, the $input variable enumerates the object that is currently in the pipeline. When the Process block completes, there are no objects left in the pipeline, so the $input variable enumerates an empty collection. If the function does not have a Process block, then in the End block, the $input variable enumerates the collection of all input to the function.