PowerShell for Windows Admins

Jun 27 2013   3:44PM GMT

Writable properties for a WMI class

Richard Siddaway Richard Siddaway Profile: Richard Siddaway

Do you know how to discover which properties on a WMI class, and therefore a WMI instance, can be modified?

Get-CimClass from the PowerShell 3.0 CIM cmdlets is the answer:

$class = Get-CimClass -ClassName win32_volume
$class.CimClassProperties

The last command returns all of the properties in this format

Name : Description
Value :
CimType : String
Flags : Property, ReadOnly, NullValue
Qualifiers : {read}
ReferenceClassName :

Name : DriveLetter
Value :
CimType : String
Flags : Property, NullValue
Qualifiers : {read, write}
ReferenceClassName :

Notice the first one has a Flag of ReadOnly and the second one has a Qualifier of write. So the question becomes how can you filter on those two items?

If you run something like this:

$class = Get-CimClass -ClassName Win32_Volume
$class.CimClassProperties |
foreach {
if ($psitem | select -ExpandProperty Qualifiers | where Name -eq ‘write’){$psitem}
if (($psitem.Flags -split ‘, ‘) -notcontains ‘Readonly’) {$psitem}
}

You will see that some properties may not be Readonly but also aren’t writable such as:

Name : NumberOfBlocks
Value :
CimType : UInt64
Flags : Property, NullValue
Qualifiers : {MappingStrings}
ReferenceClassName :

In that case we need just the writable properties

Get-CimClass -ClassName Win32_Volume |
select -ExpandProperty CimClassProperties |
foreach {
if ($psitem | select -ExpandProperty Qualifiers | where Name -eq ‘write’){$psitem}
}

This brings the results down to three properties DriveLetter, IndexingEnabled, Label

The first and last I expected – IndexEnabled was new to me

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