The Windows PowerShell environment provider lets you access Windows environment variable too. To display the value of an environment variable we can use the following syntax:

     $env:<variable-name>

In this syntax, the dollar sign ($) indicates a variable and the drive name, "env:" indicates an environment variable.

These three variables will give us an info about current user, domain and computer:

$env:username

$env:userdomain

$env:computername

There is also another interesting .NET class that will give us "domain\user"  value:

[Security.Principal.WindowsIdentity]::GetCurrent().Name