Author Posts

June 20, 2015 at 1:55 pm

What is the suggested best practice for writing a cmdlet that receives input by the pipeline with regards to the type of the parameter that receives values? For example, if the cmdlet I want to write needs a path, you expect the user to adjust the syntax used by GCI to only return System.IO.FileInfo, however if they dont and I get System.IO.DirectoryInfo objects, from the Powershell users perspective, should this raise and be left to the configured erroraction?


June 21, 2015 at 6:08 am

I'm not a programmer myself, but Tobias Weltner wrote about writing your own Cmdlets in his PowerShell book. Maybe it helps you answering your question: Your Own Cmdlets and Extensions

I can also recommend Doug Finke's book for you: PowerShell for Developers

June 22, 2015 at 5:43 pm

Hi Richard,
I managed to catch a session on Pluralsight by Jimmy Skowronski titled 'Extending Powershell' where I noticed his pattern and learnt the simple nature of this task.

namespace PowerShellCourse
  [Cmdlet(VerbsDiagnostic.Test, "Parameters")]
  public class TestParametersCommand : PSCmdlet
    [Parameter(ValueFromPipelineByPropertyName = true)]
    public string FullName { get; set; }

    [Parameter(Position = 1, ValueFromPipeline = true)]
    public FileInfo File { get; set; }

    [Parameter(ValueFromPipeline = true)]
    public DirectoryInfo Folder { get; set; }

    protected override void ProcessRecord()
      WriteObject(new { Folder = Folder, File = File, FullPath = FullName });

So pretty much all options and the basic string parameter can be made available.

June 23, 2015 at 12:00 am

Great you found out! Out of curiosity, what type of Cmdlet are you going to write? Or is this to train yourself into doing it?

June 27, 2015 at 5:41 am

Sorry Richard, I am not getting subscribed notifications?

Anyway, the cmdlet receives output from Get-ChildItem where filtered content are XML files. For a specified type (several are supported) it deserializes the XML files and searches based on a quantity of type specific criteria. For example, if you choose type A and search by first and last name matching some string, it returns all the matching XML files to the pipeline. If you switch types, the cmdlet alters the actual criteria used by that deserialized type. So all you need to know is the type and your criteria abstracted to a common parameter, like "FirstName".