Introduction to PowerShell’s [WMI] Type
The [WMI] Type technique is not for the beginner, for novices I suggest they concentrate on Get-WmiObject. Even for experienced PowerShell script writers I question the usefulness of the [WMI] Type construction. While it looks flashy, the syntax is picky, therefore I am not sure that it is better than the straightforward Get-WmiObject.
Topics for PowerShell [WMI] Type
- Get-WmiObject Refresher
- [WMI] Type – Simple Example
- [WMI] Type Get-Member
- [WMI] Type Picky Syntax
- Summary of WMI and PowerShell
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[WMI] Type – Simple Example
This example employs the called Win32_ComputerSystem. By introducing variables I highlight the WMI particular class, and also remind you to change the name of $Srv. Incidentally, neither LocalHost nor ‘.’ works for as a value for your computer name, see what I mean about [WMI] Type being picky?
# [WMI] Type example
Clear-Host
$Srv = "Longhorn"
$CimPlace = "Root\Cimv2:Win32_ComputerSystem"
[WMI]$LowDown = "$CimPlace.name=’$Srv’"
$LowDown
Note 1: The reason that the above example works is that luckily I have used the .name property, which is the correct primary key for the WMI class Win32_ComputerSystem.
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[WMI] Type Get-Member
As with other PowerShell cmdlets, once you have created the [WMI] Type object you can research its properties with Get-Member:
# PowerShell [WMI] Type Properties
Clear-Host
$Srv = "Longhorn"
[WMI]$LowDown = "Root\Cimv2:Win32_ComputerSystem.name=’$Srv’"
$LowDown | Get-Member -memberType Property [a-z]*
Note 2: With this example I have defined [WMI]$LowDown more directly.
Alternative Method [WMI] Root..
# PowerShell [WMI] Type Properties
Clear-Host
$Srv = "Longhorn"
$Stuff = [WMI]"Root\Cimv2:Win32_ComputerSystem.name=’$Srv’"
$Stuff | Get-Member -memberType Property [a-z]*
Note 3: This simply alters the position of the [WMI] Type from
[WMI]$LowDown = "Root\…
To
$Stuff = [WMI]"Root\..
Researching the Primary Key for a WMI Class
Here is an example which creates a function which extracts the primary key for any named or given WMI class.
# Function to Discover WMI Primary Keys
Clear-Host
Function Get-WmiKey
{
$Class = [WmiClass]$args[0]
$Class.Properties | `
Select @{Name="PName";Expression={$_.name}} -Expand Qualifiers | `
Where {$_.Name -eq "key"} | `
foreach {$_.Pname}
}
Get-WmiKey Win32_LogicalDisk
Note 4: The whole point of creating this function is that you can substitute any WMI class for Win32_LogicalDisk.
Note 5: Alternatively you can research WMI Classes with: WBEMTest.
Note 6: See more on PowerShell functions.
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[WMI] Type Picky Syntax (Or Silly Me?)
Clear-Host
$Hardy = ""
[WMI]$Hardy="Root\CimV2:Win32_LogicalDisk.DeviceID=’C:’"
$Hardy
Note 6: This example drove me mad. The reason was that I introduced white space in an attempt to make the command more readable. Introducing a space either side of the equals sign produced the "Invalid parameter " error. Wrong, silly me.
.DeviceID = ‘C:’" Just does not work.
Neither did introducing a space between the two sets of speech marks:
.DeviceID=’C:’ " – Wrong.
See more WMI tasks for PowerShell »
Summary of PowerShell [WMI] Type
PowerShell’s [WMI] Type technique is not for the beginner. Even for experienced PowerShell script writers I question the usefulness of the [WMI] Type construction. While it looks flashy, the syntax is picky, and I am not sure that it is better than the straightforward Get-WmiObject.
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See More Microsoft PowerShell WMI Examples:
• Home • PowerShell Get-WmiObject • Windows PowerShell • PowerShell 3.0 Network
• Win32_pingstatus • WMI Win32_NetworkAdapter • Win32_NetworkAdapterConfig
• Disable NIC • PowerShell -Filter • PowerShell -Query • PowerShell Select • Free WMI Monitor
Please email me if you have any example scripts. Also please report any factual mistakes, grammatical errors or broken links, I will be happy to correct the fault.
