Question

I have a test Windows XP SP3 clean install with power shell. It’s a very strange difference if i access WMI from PowerShell and from VBScript. From powershell:

Get-WmiObject 'Win32_OperatingSystem" | select Caption

This correctly displays “Windows XP Professional”. And same code written as VBScript:

WScript.Echo( GetObject( "winmgmts:Win32_OperatingSystem" ).Caption )

Displays “null” O_O. Why this happens?

Answer 1

Here is the VBScript equivalent:

Set wmi = GetObject("winmgmts:")
Set objSet = wmi.InstancesOf("Win32_OperatingSystem")

For Each obj in objSet
    WScript.Echo obj.Caption
    Exit For
Next

Although there is only one Operating System, a WMI query always returns a list.

Ok, now, the difference – Using the Get-WmiObject cmdlet, since there is only one operation system, you get the object directly rather than a list when you do Get-WmiObject "Win32_OperatingSystem" ( use GetType to see that this is actually of type System.Management.ManagementObject )

Since there will be multiple processes, get-wmiobject win32_process would give a array. ( use GetType to see that this is of type System.Object[]

The following would not give any output:

(get-wmiobject win32_process).Caption

Whereas the below would:

(get-wmiobject win32_process)[0].Caption