Unable to fetch user from sharepoint site using powershell

Question

$user = Get-SPuser -Web $web -Identity $UserID

Get-SPUser : You must specify a valid user object or user identity.
At line:11 char:31
+             $user = get-SPuser <<<<  -Web $web -Identity $UserID
    + CategoryInfo          : InvalidArgument: (Microsoft.Share....SPUserPipeBind:SPUserPipeBind) [Get-SPUser], PSArgumentException
    + FullyQualifiedErrorId : Microsoft.SharePoint.PowerShell.SPCmdletGetUser

$user = $web.EnsureUser($username)
Exception calling "EnsureUser" with "1" argument(s): "The specified user Krishna could not be found."

How can I verify User exists in a site or not?
How can I fetch users without any exceptions?
If user doesn't exists, add user in site and fetch user.

Answer 1

You have to ensure your user first to validate the user identity.

$web = Get-SPWeb -identity $siteCollUrl
foreach ($User in $Users) { 
    $web.EnsureUser($User)  
    Set-SPUser -Identity $User -Web $siteCollUrl -Group $group  
} 

Everything which you require is in the below link,

http://www.manasbhardwaj.net/add-users-sharepoint-group-using-powershell/