#PSTip Excluding WMI system properties

Whenever you use Windows Management Instrumentation (WMI), the result always comes back with a list of system properties. WMI system properties are associated with all classes and instances of classes, and begin with a double underscore.

PS> Get-WmiObject Win32_Processor
__GENUS                     : 2
__CLASS                     : Win32_Processor
__SUPERCLASS                : CIM_Processor
__DYNASTY                   : CIM_ManagedSystemElement
__RELPATH                   : Win32_Processor.DeviceID="CPU0"
__PROPERTY_COUNT            : 48
__DERIVATION                : {CIM_Processor, CIM_LogicalDevice, CIM_LogicalElement, CIM_ManagedSystemElement}
__SERVER                    : LOKI
__NAMESPACE                 : root\cimv2
__PATH                      : \\LOKI\root\cimv2:Win32_Processor.DeviceID="CPU0"
AddressWidth                : 64
Architecture                : 9
Availability                : 3
Caption                     : Intel64 Family 6 Model 44 Stepping 2
ConfigManagerErrorCode      :
ConfigManagerUserConfig     :
CpuStatus                   : 1
CreationClassName           : Win32_Processor
CurrentClockSpeed           : 2800
CurrentVoltage              : 33
DataWidth                   : 64
Description                 : Intel64 Family 6 Model 44 Stepping 2
(...)

Sometimes you’d want to remove system properties from the output, when constructing a report for example,  and you might attempt to do that with the ExcludeProperty parameter of the Select-Object cmdlet, but as you can see it doesn’t seem to work, all system properties are still in place.

PS> Get-WmiObject Win32_Processor | Select-Object -ExcludeProperty __*
__GENUS                     : 2
__CLASS                     : Win32_Processor
__SUPERCLASS                : CIM_Processor
__DYNASTY                   : CIM_ManagedSystemElement
__RELPATH                   : Win32_Processor.DeviceID="CPU0"
__PROPERTY_COUNT            : 48
__DERIVATION                : {CIM_Processor, CIM_LogicalDevice, CIM_LogicalElement, CIM_ManagedSystemElement}
__SERVER                    : LOKI
__NAMESPACE                 : root\cimv2
__PATH                      : \\LOKI\root\cimv2:Win32_Processor.DeviceID="CPU0"
AddressWidth                : 64
Architecture                : 9
(...)

In order to exclude them you must first include all properties. The ExcludeProperty parameter is effective only when the command also includes the Property parameter.

PS> Get-WmiObject Win32_Processor | Select-Object -Property * -ExcludeProperty __*

AddressWidth                : 64
Architecture                : 9
Availability                : 3
Caption                     : Intel64 Family 6 Model 44 Stepping 2
ConfigManagerErrorCode      :
ConfigManagerUserConfig     :
CpuStatus                   : 1
CreationClassName           : Win32_Processor
CurrentClockSpeed           : 2800
CurrentVoltage              : 33
DataWidth                   : 64
Description                 : Intel64 Family 6 Model 44 Stepping 2
(...)