Working with WMI Events (2)

re: Working with WMI Events (2)

Oisin Grehan — Mon, 16 Jul 2007 19:28:04 GMT

The only caveat here is WaitForNextEvent blocks all keyboard input you receieve an event, this includes Ctrl+C. So if you screw up, you have to kill your powershell session.

If you're more familiar with traditional .net events, the Wmi Watcher class exposes a EventArrived event. Powershell v1 doesn't have any solid support for handling sync or async events, so enter my shameless plug for my free, open-source eventing library: http://www.codeplex.com/pseventing

This library allows you to subscribe to standard events and collect them in the background while you get on with scripting:

1 PS> $watch = gwe -Class "Win32_ProcessStartTrace"

2 PS> Connect-EventListener watch eventarrived,disposed -Verbose

VERBOSE: Target is a ManagementEventWatcher

VERBOSE: Now listening for 'eventarrived' events from $watch

VERBOSE: Target is a ManagementEventWatcher

VERBOSE: Now listening for 'disposed' events from $watch

3 PS> $watch.Start()

Now, if you really want to block and wait, use:

4 PS> get-event -wait

except this time you can break out with ctrl+c at any time.

alternatively, continue scripting away and check for events with get-event:

4 PS> $events = get-event

5 PS> $events | ft -auto

Occurred Source Name Args

-------- ------ ---- ----

07/16/2007 12:24 PM System.Management.Automation.PSVariable EventArrived System.Management.EventArrivedEventArgs

Btw, the Source property is a reference to the $watch variable. I believe powershell v2 has some kind of event handling, and I'd be interested to hear more about it from you guys. You've been suspiciously quiet about it all ;-)

Thanks guys for a great product!

- Oisin / x0n

re: Working with WMI Events (2)

kmathur — Tue, 17 Jul 2007 09:03:56 GMT

Nice! A plugin to support async eventing for powershell. Interesting project.

Working with WMI Events in powershell

kapslock — Tue, 17 Jul 2007 10:13:42 GMT

I posted the following on Powershell team's blog - Powershell V1 does not give a cmdlet to support WMI

Working with WMI Events in powershell

Noticias externas — Tue, 17 Jul 2007 10:19:23 GMT

I posted the following on Powershell team's blog - Powershell V1 does not give a cmdlet to support

re: Working with WMI Events (2)

Wolfmandragon — Mon, 23 Jul 2007 19:36:55 GMT

When I run this script I get an error message of for the line of

$result = $watch.WaitForNextEvent()

exception calling "WaitForNextEvent()" with "0" argument(s): "Unparsable query. "

if I take out "()" then I get no error message but there is also no event logs raised. Could someone explain this please.