Exploring Get-EventSubscriber in PowerShell

Welcome back to Wahmans Powershell blog! Today we’re diving into a lesser-known but incredibly useful cmdlet: Get-EventSubscriber. This cmdlet might not be something you use every day, but it plays a vital role when working with event-driven programming in PowerShell. As defined by Microsoft, Get-EventSubscriber gets the event subscribers in the current session.

So what does that mean? In PowerShell, it’s possible to subscribe to events—like timers ticking, files changing, or WMI events firing. These subscriptions register something called an “event subscriber”. The Get-EventSubscriber cmdlet lets you inspect what events you’re currently subscribed to and manage them as needed.

Why Use Get-EventSubscriber?

• Debug event-based scripts
• List active event listeners
• Stop outdated or unwanted event subscriptions
• Monitor system or application triggers you’ve set up

Let’s Explore With Some Examples!

Example 1: List Current Event Subscribers (Beginner)

This is the simplest use—just list the current in-session event subscribers:

Get-EventSubscriber

If you have not created any subscriptions yet, this will return nothing.

Example 2: Create and View a Timer Subscription (Intermediate)

Let’s create a simple event subscription using a timer:

$timer = New-Object Timers.Timer
$timer.Interval = 1000
$timer.AutoReset = $true
Register-ObjectEvent -InputObject $timer -EventName Elapsed -SourceIdentifier TimerElapsed -Action { Write-Host "Timer elapsed!" }

# View the subscriber
Get-EventSubscriber

This code sets up a timer that triggers every second. Run Start-Sleep -Seconds 5 to let it run briefly and observe the events firing.

Example 3: Removing an Event Subscriber (Intermediate)

Now that we’re creating subscribers, let’s learn to remove them using their SourceIdentifier:

Unregister-Event -SourceIdentifier TimerElapsed
Get-EventSubscriber

After running this, you’ll see that your subscription has been removed.

Example 4: Subscribe to WMI Events (Advanced)

You can subscribe to more complex sources—like WMI events. Here’s an example that notifies you when a USB device is plugged in:

Register-WmiEvent -Query "SELECT * FROM Win32_DeviceChangeEvent WHERE EventType = 2" -SourceIdentifier USBInserted -Action {
    Write-Host "A USB device was inserted!"
}

# Check active subscribers
Get-EventSubscriber

This uses WMI to detect hardware changes. Be sure to test this on a system where you can safely insert/remove USB devices.

Wrap-Up

Get-EventSubscriber is a great diagnostic and management tool for your event-driven PowerShell scripts. Understanding how to monitor and manage your event subscriptions can help you write more robust and responsive tools.

Happy scripting, and I will see you in the next post!