Powershell function to add a user to a local group

addLocalUser.ps1

function Add-LocalUser{
     Param(
        $computer=$env:computername,
        $group='Guests',
        $userdomain=$env:userdomain,
        $username=$env:username
    )
        ([ADSI]"WinNT://$computer/$Group,group").psbase.Invoke("Add",([ADSI]"WinNT://$domain/$user").path)
}

#Non-powershell equiv:
#net localgroup administrators mydomain.local\user1 /add