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Register-EngineEvent

  • Reference
Module:
Microsoft.PowerShell.Utility

Subscribes to events that are generated by the PowerShell engine and by the New-Event cmdlet.

Syntax

Register-EngineEvent
        [-SourceIdentifier] <String>
        [[-Action] <ScriptBlock>]
        [-MessageData <PSObject>]
        [-SupportEvent]
        [-Forward]
        [-MaxTriggerCount <Int32>]
        [<CommonParameters>]

Description

The Register-EngineEvent cmdlet subscribes to events that are generated by the PowerShell engine and the New-Event cmdlet. Use the SourceIdentifier parameter to specify the event.

You can use this cmdlet to subscribe to the OnIdle or Exiting engine events and events generated by the New-Event cmdlet. These events are automatically added to the event queue in your session without subscribing. However, subscribing lets you forward the events, specify an action to respond to the events, and cancel the subscription.

When you subscribe to an event, an event subscriber is added to your session. To get the event subscribers in the session, use the Get-EventSubscriber cmdlet. To cancel the subscription, use the Unregister-Event cmdlet, which deletes the event subscriber from the session.

When the subscribed event is raised, it is added to the event queue in your session. To get events in the event queue, use the Get-Event cmdlet.

Examples

Example 1: Register a PowerShell engine event on remote computers

This example registers for a PowerShell engine event on two remote computers.

$S = New-PSSession -ComputerName "Server01, Server02"
Invoke-Command -Session $S {
  Register-EngineEvent -SourceIdentifier ([System.Management.Automation.PsEngineEvent]::Exiting) -Forward
}

New-PSSession creates a user-managed session (PSSession) on each of the remote computers.The Invoke-Command cmdlet runs the Register-EngineEvent command in the remote sessions. Register-EngineEvent uses the SourceIdentifier parameter to identify the event. The Forward parameter tell the engine to forward the events from the remote session to the local session.

Example 2: Take a specified action when the Exiting event occurs

This example shows how to run Register-EngineEvent to take a specific action when the PowerShell.Exiting event occurs.

Register-EngineEvent -SourceIdentifier PowerShell.Exiting -SupportEvent -Action {
    Get-History | Export-Clixml $HOME\history.clixml
}

The SupportEvent parameter is added to hide the event subscription. When PowerShell exits, in this case, the command history from the exiting session is exported an XML file in the user's $HOME directory.

Example 3: Create and subscribe to a user-defined event

This example creates a subscription for events from the source MyEventSource. This is an arbitrary source that we are going to use to monitor the progress of a job. Register-EngineEvent is used to create the subscription. The script block for the Action parameter logs the event data to a text file.

Register-EngineEvent -SourceIdentifier MyEventSource -Action {
    "Event: {0}" -f $event.messagedata | Out-File c:\temp\MyEvents.txt -Append
}

Start-Job -Name TestJob -ScriptBlock {
    While ($True) {
        Register-EngineEvent -SourceIdentifier MyEventSource -Forward
        Start-Sleep -seconds 2
        "Doing some work..."
        New-Event -SourceIdentifier MyEventSource -Message ("{0} -  Work done..." -f (Get-Date))
    }
}
Start-Sleep -seconds 4
Get-EventSubscriber
Get-Job

SubscriptionId   : 12
SourceObject     :
EventName        :
SourceIdentifier : MyEventSource
Action           : System.Management.Automation.PSEventJob
HandlerDelegate  :
SupportEvent     : False
ForwardEvent     : False

Id     Name            PSJobTypeName   State         HasMoreData     Location             Command
--     ----            -------------   -----         -----------     --------             -------
18     MyEventSource                   Running       True                                 …
19     TestJob         BackgroundJob   Running       True            localhost            …

Register-EngineEvent created Job Id 18. Start-Job created Job Id 19. In Example #4, we remove the event subscription and the jobs, then inspect the log file.

Example 4: Unregister events and clean up jobs

This is a continuation of Example 3. In this example we wait for 10 seconds to let several events occur. Then we unregister the event subscription.

PS> Start-Sleep -seconds 10
PS> Get-EventSubscriber | Unregister-Event
PS> Get-Job

Id     Name            PSJobTypeName   State         HasMoreData     Location             Command
--     ----            -------------   -----         -----------     --------             -------
18     MyEventSource                   Stopped       False                                …
19     TestJob         BackgroundJob   Running       True            localhost            …

PS> Stop-Job -Id 19
PS> Get-Job | Remove-Job
PS> Get-Content C:\temp\MyEvents.txt
Event: 2/18/2020 2:36:19 PM -  Work done...
Event: 2/18/2020 2:36:21 PM -  Work done...
Event: 2/18/2020 2:36:23 PM -  Work done...
Event: 2/18/2020 2:36:25 PM -  Work done...
Event: 2/18/2020 2:36:27 PM -  Work done...
Event: 2/18/2020 2:36:29 PM -  Work done...
Event: 2/18/2020 2:36:31 PM -  Work done...

The Unregister-Event cmdlet stops the job associated with the event subscription (Job Id 18). Job Id 19 is still running and creating new events. We use the Job cmdlets stop the job and remove the unneeded job objects. Get-Content displays the contents of the log file.

Parameters

-Action

Specifies commands to handle the events. The commands in the Action run when an event is raised, instead of sending the event to the event queue. Enclose the commands in braces ({}) to create a script block.

The value of the Action parameter can include the $Event, $EventSubscriber, $Sender, $EventArgs, and $Args automatic variables, which provide information about the event to the Action script block. For more information, see about_Automatic_Variables.

When you specify an action, Register-EngineEvent returns an event job object that represents that action. You can use the Job cmdlets to manage the event job.

Type:ScriptBlock
Position:101
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:False

-Forward

Indicates that the cmdlet sends events for this subscription to the session on the local computer. Use this parameter when you are registering for events on a remote computer or in a remote session.

Type:SwitchParameter
Position:Named
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:False

-MaxTriggerCount

Specifies the maximum number of times that the action is executed for the event subscription.

Type:Int32
Position:Named
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:False

-MessageData

Specifies additional data associated with the event. The value of this parameter appears in the MessageData property of the event object.

Type:PSObject
Position:Named
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:False

-SourceIdentifier

Specifies the source identifier of the event to which you are subscribing. The source identifier must be unique in the current session. This parameter is required.

The value of this parameter appears in the value of the SourceIdentifier property of the subscriber object and of all event objects associated with this subscription.

The value is specific to the source of the event. This can be an arbitrary value you created to use with the New-Event cmdlet. The PowerShell engine supports the PSEngineEvent values PowerShell.Exiting and PowerShell.OnIdle.

Type:String
Position:100
Default value:None
Required:True
Accept pipeline input:False
Accept wildcard characters:False

-SupportEvent

Indicates that the cmdlet hides the event subscription. Add this parameter when the current subscription is part of a more complex event registration mechanism and it should not be discovered independently.

To view or cancel a subscription that was created with the SupportEvent parameter, add the Force parameter to the Get-EventSubscriber or Unregister-Event cmdlets.

Type:SwitchParameter
Position:Named
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:False

Inputs

None

You can't pipe objects to this cmdlet.

Outputs

None

By default, this cmdlet returns no output.

PSEventJob

When you use the Action parameter, this cmdlet returns a PSEventJob object.

Notes

Events, event subscriptions, and the event queue exist only in the current session. If you close the current session, the event queue is discarded and the event subscription is canceled.

When subscribing to the Exiting event, the cmdlets that can be executed by the Action parameter are limited to the cmdlets in the Microsoft.PowerShell.Core and Microsoft.PowerShell.Utility modules. The Exiting event is only fired when the session is exited under the control of PowerShell. The event is not fired when the host application or terminal window is closed.

The engine is considered to be idle if it is not running a pipeline. The OnIdle event is fired when PowerShell has been idle for 300 milliseconds (ms).

Note

When PSReadLine is in use, the OnIdle event is fired when ReadKey() times out (no typing in 300ms). The event could be signaled while the user is in the middle of editing a command line, for example, the user is reading help to decide which parameter to use. Beginning in PSReadLine 2.2.0-beta4, OnIdle behavior changed to signal the event only if there is a ReadKey() timeout and the current editing buffer is empty.