Is it possible to terminate or stop a PowerShell pipeline from within a filter

Question

I have written a simple PowerShell filter that pushes the current object down the pipeline if its date is between the specified begin and end date. The objects coming down

Answer 1

If you're willing to use non-public members here is a way to stop the pipeline. It mimics what select-object does. invoke-method (alias im) is a function to invoke non-public methods. select-property (alias selp) is a function to select (similar to select-object) non-public properties - however it automatically acts like -ExpandProperty if only one matching property is found. (I wrote select-property and invoke-method at work, so can't share the source code of those).

# Get the system.management.automation assembly
$script:smaa=[appdomain]::currentdomain.getassemblies()|
         ? location -like "*system.management.automation*"
# Get the StopUpstreamCommandsException class 
$script:upcet=$smaa.gettypes()| ? name -like "*StopUpstreamCommandsException *"

function stop-pipeline {
    # Create a StopUpstreamCommandsException
    $upce = [activator]::CreateInstance($upcet,@($pscmdlet))

    $PipelineProcessor=$pscmdlet.CommandRuntime|select-property PipelineProcessor
    $commands = $PipelineProcessor|select-property commands
    $commandProcessor= $commands[0]

    $ci = $commandProcessor|select-property commandinfo
    $upce.RequestingCommandProcessor | im set_commandinfo @($ci)

    $cr = $commandProcessor|select-property commandruntime
    $upce.RequestingCommandProcessor| im set_commandruntime @($cr)

    $null = $PipelineProcessor|
        invoke-method recordfailure @($upce, $commandProcessor.command)

    if ($commands.count -gt 1) {
      $doCompletes = @()
      1..($commands.count-1) | % {
        write-debug "Stop-pipeline: added DoComplete for $($commands[$_])"
        $doCompletes += $commands[$_] | invoke-method DoComplete -returnClosure
      }
      foreach ($DoComplete in $doCompletes) {
        $null = & $DoComplete
      }
    }

    throw $upce
}

---

EDIT: per mklement0's comment:

Here is a link to the Nivot ink blog on a script on the "poke" module which similarly gives access to non-public members.

As far as additional comments, I don't have meaningful ones at this point. This code just mimics what a decompilation of select-object reveals. The original MS comments (if any) are of course not in the decompilation. Frankly I don't know the purpose of the various types the function uses. Getting that level of understanding would likely require a considerable amount of effort.

My suggestion: get Oisin's poke module. Tweak the code to use that module. And then try it out. If you like the way it works, then use it and don't worry how it works (that's what I did).

Note: I haven't studied "poke" in any depth, but my guess is that it doesn't have anything like -returnClosure. However adding that should be easy as this:

if (-not $returnClosure) {
  $methodInfo.Invoke($arguments)
} else {
  {$methodInfo.Invoke($arguments)}.GetNewClosure()
}

Answer 2

You can throw an exception when ending the pipeline.

gc demo.txt -ReadCount 1 | %{$num=0}{$num++; if($num -eq 5){throw "terminated pipeline!"}else{write-host $_}}

or

Look at this post about how to terminate a pipeline: https://web.archive.org/web/20160829015320/http://powershell.com/cs/blogs/tobias/archive/2010/01/01/cancelling-a-pipeline.aspx