Building PowerShell Applications: A Step-by-Step Guide

In a recent article, I discussed the process of making a RESTful API call from PowerShell and displaying the retrieved data (Getting Started With RESTful APIs in PowerShell). As useful as that technique might be, there is a big difference between making an API call and building an application.

With that in mind, I’d like to explore what it takes to build a full-blown application in PowerShell.

My primary goal in writing this article series is to teach advanced PowerShell coding techniques. I also wanted the app I developed to meet several criteria:

Needless to say, achieving these goals using PowerShell requires a lot of work, but it is indeed possible.

My Plan for This Series

In this article series, I plan to follow a structured approach:

Related:ChatGPT Integration in PowerShell (Scripting Demo)

Finally, I will provide my app’s full source code at the end of Part 3.

Data Sources

Most modern applications share a common characteristic: They rely on multiple data sources. While designing a PowerShell script capable of making API calls is nice, custom applications often require data from diverse origins. The odds are that you aren’t going to be able to find a single API that does everything you need.

As such, I aimed to build a script that uses multiple public data sources. Specifically, the script incorporates an API (requiring multiple API calls) and a local data repository.

Before delving into the specifics of the data sources, let me first explain what the script does. The script I have created serves as a weather forecast application.

Here’s an overview of what the script accomplishes:

Complex PowerShell 1-1

Figure 1. The script prompts you to enter your zip code.

Complex PowerShell 1-2

Figure 2. The script provides a graphical weather forecast for the location that you have specified.

As noted earlier, this script relies on multiple external data sources:

Strategies for Writing Complex PowerShell Scripts

As you begin to develop advanced PowerShell scripts, you may discover that the sheer complexity of the task becomes overwhelming. Fortunately, there are several strategies to make the process more manageable.

One commonly used technique for handling complex PowerShell development tasks is to break the script into modules. A module is essentially a standalone function or component of a script. Using modules makes it easier to focus on building and debugging one part of the script at a time. I didn’t use modules for the script I am presenting in this series, but I may revisit this topic in the future.

Even if you choose not to use modules, you can still develop a complex script by breaking it into separate parts and then merging them when complete. For example, when creating the script I am going to be discussing, I initially built a bare-bones version with no regard for aesthetics. My primary objective was to validate the API calls and establish the fundamental script logic.

I also developed a separate script that contained a user interface but with no logic or real-world data (although I created some placeholder data). This approach allowed me to concentrate on individual aspects of the script (interface and functionality) separately, without needlessly complicating the development process.

Additionally, it is also worth noting that I built the user interface before writing any functional code. This choice was deliberate. By creating the user interface first, I could make decisions as to exactly which data elements the script would expose (the API returns far more data than what the script uses). Knowing exactly what data would be displayed and which elements were present within the user interface made it much easier to write the functional portion of the script.

So, with that said, let’s begin dissecting the script’s logic. I will show you how the data portion of the script works in Part 2.