PowerShell Standard Library: Build single module that works across Windows PowerShell and PowerShell Core

This is the first of a series of blog posts that will help you take advantage of a new NuGet package PowerShellStandard Library 5.1.0. This package allows developers to create modules that are portable between Windows PowerShell 5.1 and PowerShell Core 6.0. This means that you can create PowerShell modules that run on Windows, Linux, and macOS with a single binary!

The version of PowerShell Standard Library indicates the lowest version of PowerShell that it is compatible with. The community promise is that it is always forward compatible. So a module built against PowerShell Standard Library v3 is compatible with Windows PowerShell v3, v4, v5.1, PowerShell Core 6, and the upcoming PowerShell Core 6.1. Compatibility is achieved by providing a subset of the APIs common across all those versions of PowerShell. This reference assembly is the equivalent to a header file for C/C++ where it has the APIs defined, but no implementation. During runtime, the module would use the version of System.Management.Automation.dll that is used by the PowerShell host.

Creating a PowerShell Module

In this post, I’ll walk through the steps for creating a simple C# module with a single cmdlet. I will also be using the DotNet CLI tools for creating everything I need.

Installing the PowerShell Standard Module Template

First, we can leverage a new template that we published for DotNet CLI, but we need to install it first:

A new template called psmodule is now available making it easy to start a new C# based PowerShell module. Any issues, feedback, or suggestions for this template should be opened in the PowerShell Standard repo.

Creating a new project

We need to create a location for our new project and then use the template to create the project:

You can see that the dotnet cli has created a source file and .csproj file for my project:

The sample from the template demonstrates a simple cmdlet with two parameters that outputs results with a custom class.

Building the module

Building the sample is code is easy with DotNet CLI:

Testing the built module

To test this sample module, we just need to import it. We can check to see what it supports and try running it:

This sample is pretty simple as it’s intended to just show how to get started on writing a PowerShell module from scratch. The important point is that using PowerShell Standard Library, this assembly can be used in both PowerShell Core 6 as well as Windows PowerShell. This sample will even work on Windows, Linux, or macOS without any changes.

In the next part of this series, I’ll cover other aspects of PowerShell module authoring such as module manifests and writing Pester tests.

James Truher
Senior Software Engineer
PowerShell Team