How and When to Create and Use PowerShell Modules

What is a PowerShell module?

A PowerShell module is a grouping of functions and code around a central theme. Modules are created for applications such as Microsoft Exchange, Active Directory, and VMware. You can even manage IIS application pools using PowerShell. 

Beyond applications, modules can be used for print management, network adapter configurations, and more. Modules are always created to manage a central theme or object.

There are four different PowerShell modules:

• Script modules are PSM1 files that typically contain functions, but they can contain any valid PowerShell code.
• Binary modules are compiled DLL files typically not created by IT pros. That task is usually left to developers.
• Manifest modules are script modules that contain a manifest.
• Dynamic modules are never written to disk and are available only in memory.

Module types serve specific purposes, but you’re most likely to create script modules. Script modules don’t require knowledge of C# or the compilation process. They’re the most common module type, especially among IT pros.

William Mabotja, an Azure-certified senior software developer at Atlas Finance, emphasized the importance of PowerShell modules for automation and script management. “They offer numerous benefits that enhance coders’ productivity,” Mabotja said. “At their core, modules bundle related functions, cmdlets, and scripts together so they’re more efficiently organized and allow for better management of PowerShell code.”

Mabotja noted that this modularity simplifies the development process while improving code reliability and enhancing workplace collaboration.

When should you create a PowerShell module?

You can easily decide whether to create a module by answering the following questions while writing a script:

• Will the code I’m writing need to be used more than once?
• Does this code essentially manage a single object or entity?
• As I write this code, do I find that I’m breaking it apart into functions because it’s getting too complex to be in a single script?
• Do I need to share the code with others?

If you answered yes to at least three of these questions, you should probably write a module instead of a PS1 script.

Mabotja stressed that specialized functionality is one of PowerShell’s primary advantages. “Whether you need to manage email, handle cloud storage, or oversee identity management, there will almost certainly be a module available already to meet your needs,” he said. “This extensive library acts like a massive toolbox for developers to handle various different coding challenges, particularly around automation.”

How do I create a PowerShell module?

Open Notepad. Save the file with a PSM1 extension. Done.

No, really, that’s it. That’s all it takes to create a script module. Granted, it won’t be a very functional module, but, technically, it’s a script module. Let’s concentrate on something more useful though. 

Examples are always a great way to demonstrate a concept, so let’s create a module to manage houses in a subdivision. This isn’t a practical example (at least not until the PowerShell team figures out how to integrate PowerShell into the physical world), but it will demonstrate a little of what a module is capable of. (In more practical situations, you could use PowerShell to create a web-scraping tool, for example.)

Every function is there, including the ability to:

• Create new houses
• Find all the houses created
• Modify the houses
• Remove houses

The houses managed with this module happen to be in the fancy subdivision neighborhood, so it’s good practice to set that as a module variable at the top. That way, you can reference that variable in any of the PowerShell functions, making it easier to improve your code’s readability and maintenance.

If you want to share the module with your contractors but don’t want them to build any new houses or remove any houses without your permission, you should allow them only the Get-* functions and Set-* functions. Similarly, you can use PowerShell to manage user profiles and control users’ permissions.

But because you want your contractors to be able to tell what neighborhood they’ll be working in, you allow them to see the value of $Neighborhood in their PowerShell console.

When creating modules, Mabotja recommends coders follow best practices for naming conventions, documentation, and structuring their code to ensure others can easily understand and maintain existing modules.

How do you use a PowerShell module?

Now you have the house module created; let’s call it House.psm1. If you want your contractors to use it, place it in a shared folder called HOMESERVERfileshare on your network (try syncing folders with PowerShell so all contractors have the latest module version). 

Next, tell each contractor to open their PowerShell console and import it.

Importing the module brings all the functions and variables into each contractor’s PowerShell session.

You can see that they can run Get-House and Set-House, but the moment they try to run Remove-House, PowerShell throws an error. That’s because PowerShell doesn’t recognize the function. You didn’t allow it to load into the current session. 

At this point, they can still use the module without a problem. If they close the console and open it again, however, the Remove-House function will not be available.

Whenever you run Import-Module (or use PowerShell’s auto-loading feature), it loads only the module in the current session. It will not load it again. The contractor must either load the module again or, preferably, place the module into the PsModulePath so it auto-loads the next time a House function is needed.

That should get you started using modules.

Best practices for working with PowerShell modules 

Mabotja offered the following advice to people who are new to creating and using PowerShell modules. 

• Pay attention to version compatibility. As you begin working with modules, Mabotja advised, keep version compatibility in mind. “Version compatibility is a frequent issue,” Mabotja said. “Some modules work only with PowerShell 7, while others may not support it at all. Always check the PowerShell version required for the modules you use.” 
• Explore the PowerShell Gallery. Newbies should start by exploring the PowerShell Gallery, which offers a vast collection of reliable and well-documented prebuilt modules. “Begin with official modules to build a solid foundation, then gradually experiment with custom modules,” Mabotja said. “Tutorials, forums, and interactive lessons can also provide valuable support as you learn. Remember, practice is key!”

Mark Fairlie contributed to this article.