Prof. Powershell

Practical PowerShell Part 2: Property Value

This week Prof. PowerShell shows you how to retrieve dynamic property values.

• By Jeffery Hicks
• 07/15/2014

More on this topic:

• Practical PowerShell Part 1: 1-Line Commands
• Practical PowerShell Part 3: Create Custom Objects Quickly
• Practical PowerShell Part 4: Output Formatting
• Practical PowerShell Part 5: Remoting

In last week's lesson we started exploring a PowerShell command and identifying ways to use it. If you want to follow along, open a command prompt and run through the command line examples from the last article to get caught up.

I need to verify that I can retrieve the value from each dynamic property. Here's a quick recap of where we're at:

PS C:\> $regentry = Get-ItemProperty -Path HKLM:\SOFTWARE\RegisteredApplications | Select -Property * -ExcludeProperty $exclude
PS C:\> $props = $regentry.psobject.properties.name

The $props variable contains an array of property names for things in $regentry.

PS C:\> $props[0]
Paint

How about a quick test?

PS C:\> $regentry.$($props[0])
SOFTWARE\Microsoft\Windows\CurrentVersion\Applets\Paint\Capabilities

Excellent. Remember, my goal is to also get some information from the corresponding value. I am assuming this path is relative to HKLM so I will use Join-Path to construct a valid path which I can use with Get-Item.

PS C:\> Join-Path HKLM: $regentry.$($props[0]) | Get-Item

Or if I just want the properties:

PS C:\> Join-Path HKLM: $regentry.$($props[0]) | Get-ItemProperty | Select App*

Now that I've proved how to do something for one item in my list of registered applications I can do it for all using ForEach-Object.

foreach ($entry in $props) {
$valuepath = Join-Path -path "HKLM:" -child $regentry.$entry
Get-ItemProperty -Path $valuePath | Select App*
}

As you can see in Figure 3, it is possible some applications may not have anything at the specified location. I will have to handle that error when it comes time to build a reusable script. I always prefer writing objects to the pipeline. I could take what I have discovered so far and use Select-Object to create a custom object for each registered application.

$props | Select @{Name="Application";Expression={$_}},
@{Name="Entry";Expression={$regentry.$_}},
@{Name="Name";Expression={
(Join-Path -path "HKLM:" -child $regentry.$_ | Get-ItemProperty).ApplicationName}},
@{Name="Description";Expression={
(Join-Path -path "HKLM:" -child $regentry.$_ | Get-ItemProperty).ApplicationDescription}}

As you can see in Figure 4 this works, although perhaps it isn't that easy to follow. The $_ place holder is the name of each registered application which is used as a dynamic property of the previously created $regentry variable. Of course I could add and delete properties at will. Although personally, I have a goal to write or use a command only once and in this instance I am creating the same path and getting the same registry property twice. Yes, the performance hit is negligible, but I prefer something a bit more efficient. That is what we will look at next time.