get Current user context
You could use the WindowsIdentity class to get the current thread user:
[Security.Principal.WindowsIdentity]::GetCurrent()
If you need to know the actual user:
[reflection.assembly]::LoadWithPartialName("System.DirectoryServices.AccountManagement")[System.DirectoryServices.AccountManagement.UserPrincipal]::Current
Use:
[System.DirectoryServices.AccountManagement.UserPrincipal]::Current | gm
to know available properties/methods of UserPrincipal
.