Richard Siddaway's Blog

WMI is installed as a series of providers. The information on creating the classes comes from MOF files. I was recently asked about a problem with a specific class & could it be restored – in this case it was easier to rebuild WMI as the provider created a large part of the root\cimv2 namespace (namespaces can require multiple namespaces to complete their creation).

That got me thinking about how you discover the mof file associated with a class. Which leads to

$ns = "root\cimv2"            
$class = "Win32_Logicaldisk"            
            
            
$p = Get-WmiObject -Namespace $ns -Class $class |             
select -f 1 |             
select -ExpandProperty qualifiers |             
where {$_.Name -eq 'provider'}            
            
$class            
$p            
            
Get-ChildItem -Path C:\Windows\System32\wbem -Filter "*$($p.Value)*"

Get the first instance of a class, expand the qualifiers and select the qualifier with a name of provider.

Then perform a dir on the wbem folder to find the appropriate files. This isn’t infallible due to files names not necessarily being consistent but its a good starting point for the standard classes

There are many people who don’t like to see the WMI system properties

PS> Get-WmiObject -Class Win32_OperatingSystem | select __*

__GENUS          : 2
__CLASS          : Win32_OperatingSystem
__SUPERCLASS     : CIM_OperatingSystem
__DYNASTY        : CIM_ManagedSystemElement
__RELPATH        : Win32_OperatingSystem=@
__PROPERTY_COUNT : 63
__DERIVATION     : {CIM_OperatingSystem, CIM_LogicalElement, CIM_ManagedSystemElement}
__SERVER         : RSLAPTOP01
__NAMESPACE      : root\cimv2
__PATH           : \\RSLAPTOP01\root\cimv2:Win32_OperatingSystem=@

Now one day we may get a version of Get-WmiObject that allows us to block their display but in the mean time we can create a proxy function.

Using the metaprogramming module from

http://blogs.msdn.com/powershell/archive/2009/01/04/extending-and-or-modifing-commands-with-proxies.aspx

I created a proxy function

New-ProxyCommand Get-WmiObject -CommandType All
-AddParameter NoSystemProperties > Get-WmiObject.ps1

This adds a parameter NoSystemProperties and outputs everything to a .ps1 file.

The details need to be added:

1. turn the script into a function
2. add the [switch] type to the property
3. add the code to deal with the new parameter

if ($NoSystemProperties) {
[Void]$PSBoundParameters.Remove("NoSystemProperties")
$scriptCmd = {& $wrappedCmd @PSBoundParameters |
Select-Object -ExcludeProperty __*  -Property *|
Select-Object -ExcludeProperty Scope, Path, Options, ClassPath,
Properties, SystemProperties, Qualifiers, Site, Container -Property * }
}
else {
$scriptCmd = {& $wrappedCmd @PSBoundParameters }
}

If the NoSystemProperties parameter is given then remove it from the bound parameters and then run get-wmiobject, exclude the system properties and then exclude the other related properties

If the NoSystemProperties isn’t set then run as normal

function Get-WmiObject {            
            
[CmdletBinding(DefaultParameterSetName='query')]            
param(            
    [Parameter(ParameterSetName='query', Mandatory=$true, Position=0)]            
    [Parameter(ParameterSetName='list', Position=1)]            
    [System.String]            
    ${Class},            
            
    [Parameter(ParameterSetName='list')]            
    [Switch]            
    ${Recurse},            
            
    [Parameter(ParameterSetName='query', Position=1)]            
    [System.String[]]            
    ${Property},            
            
    [Parameter(ParameterSetName='query')]            
    [System.String]            
    ${Filter},            
            
    [Switch]            
    ${Amended},            
            
    [Parameter(ParameterSetName='query')]            
    [Parameter(ParameterSetName='WQLQuery')]            
    [Switch]            
    ${DirectRead},            
            
    [Parameter(ParameterSetName='list')]            
    [Switch]            
    ${List},            
            
    [Parameter(ParameterSetName='WQLQuery', Mandatory=$true)]            
    [System.String]            
    ${Query},            
            
    [Switch]            
    ${AsJob},            
            
    [Parameter(ParameterSetName='class')]            
    [Parameter(ParameterSetName='WQLQuery')]            
    [Parameter(ParameterSetName='query')]            
    [Parameter(ParameterSetName='list')]            
    [Parameter(ParameterSetName='path')]            
    [System.Management.ImpersonationLevel]            
    ${Impersonation},            
            
    [Parameter(ParameterSetName='WQLQuery')]            
    [Parameter(ParameterSetName='class')]            
    [Parameter(ParameterSetName='path')]            
    [Parameter(ParameterSetName='query')]            
    [Parameter(ParameterSetName='list')]            
    [System.Management.AuthenticationLevel]            
    ${Authentication},            
            
    [Parameter(ParameterSetName='class')]            
    [Parameter(ParameterSetName='list')]            
    [Parameter(ParameterSetName='path')]            
    [Parameter(ParameterSetName='WQLQuery')]            
    [Parameter(ParameterSetName='query')]            
    [System.String]            
    ${Locale},            
            
    [Parameter(ParameterSetName='query')]            
    [Parameter(ParameterSetName='WQLQuery')]            
    [Parameter(ParameterSetName='list')]            
    [Parameter(ParameterSetName='path')]            
    [Parameter(ParameterSetName='class')]            
    [Switch]            
    ${EnableAllPrivileges},            
            
    [Parameter(ParameterSetName='list')]            
    [Parameter(ParameterSetName='class')]            
    [Parameter(ParameterSetName='WQLQuery')]            
    [Parameter(ParameterSetName='path')]            
    [Parameter(ParameterSetName='query')]            
    [System.String]            
    ${Authority},            
            
    [Parameter(ParameterSetName='WQLQuery')]            
    [Parameter(ParameterSetName='path')]            
    [Parameter(ParameterSetName='class')]            
    [Parameter(ParameterSetName='query')]            
    [Parameter(ParameterSetName='list')]            
    [System.Management.Automation.PSCredential]            
    ${Credential},            
            
    [System.Int32]            
    ${ThrottleLimit},            
            
    [Parameter(ParameterSetName='list')]            
    [Parameter(ParameterSetName='WQLQuery')]            
    [Parameter(ParameterSetName='path')]            
    [Parameter(ParameterSetName='class')]            
    [Parameter(ParameterSetName='query')]            
    [Alias('Cn')]            
    [ValidateNotNullOrEmpty()]            
    [System.String[]]            
    ${ComputerName},            
            
    [Parameter(ParameterSetName='list')]            
    [Parameter(ParameterSetName='path')]            
    [Parameter(ParameterSetName='class')]            
    [Parameter(ParameterSetName='WQLQuery')]            
    [Parameter(ParameterSetName='query')]            
    [Alias('NS')]            
    [System.String]            
    ${Namespace},            
                
    [Switch]            
    ${NoSystemProperties})            
            
begin            
{            
    try {            
        $outBuffer = $null            
        if ($PSBoundParameters.TryGetValue('OutBuffer', [ref]$outBuffer))            
        {            
            $PSBoundParameters['OutBuffer'] = 1            
        }            
        $wrappedCmd = $ExecutionContext.InvokeCommand.GetCommand('Get-WmiObject', [System.Management.Automation.CommandTypes]::Cmdlet)            
        if ($NoSystemProperties) {            
          [Void]$PSBoundParameters.Remove("NoSystemProperties")            
          $scriptCmd = {& $wrappedCmd @PSBoundParameters |             
             Select-Object -ExcludeProperty __*  -Property *|             
             Select-Object -ExcludeProperty Scope, Path, Options, ClassPath, Properties, SystemProperties, Qualifiers, Site, Container -Property * }            
        }            
        else {            
          $scriptCmd = {& $wrappedCmd @PSBoundParameters }            
        }              
        $steppablePipeline = $scriptCmd.GetSteppablePipeline($myInvocation.CommandOrigin)            
        $steppablePipeline.Begin($PSCmdlet)            
    } catch {            
        throw            
    }            
}            
            
process            
{            
    try {            
        $steppablePipeline.Process($_)            
    } catch {            
        throw            
    }            
}            
            
end            
{            
    try {            
        $steppablePipeline.End()            
    } catch {            
        throw            
    }            
}            
            
<#

.ForwardHelpTargetName Get-WmiObject
.ForwardHelpCategory Cmdlet

#>            
            
}

The new function can be dot sourced or loaded from a module and because PowerShell runs functions before cmdlets it intercepts the cmdlet.

Get-WmiObject -Class Win32_OperatingSystem

Get-WmiObject -Class Win32_OperatingSystem –NoSystemProperties

then give us what we want.

The drawback is that using –NoSystemProperties we lose the methods but if you want them then you are either putting the results into an object or onto the pipeline in which case the system properties won’t be displayed.

Until we get a change to the cmdlet this will work.

Enjoy.