Messing Around With PowerShell 6

Starting with PowerShell 6, the whole language is open source. You’ve probably heard about that already. But if you don’t think of yourself as a “developer”, then it’s possible that the most you’ve ever taken advantage of that fact is creating a GitHub issue or commenting on a PR. Today, follow along with me, and we’ll change that.

If you’re at all comfortable writing PowerShell, you’ll be able to pick up C# with relative convenience. To be fair, dabbling with editing PowerShell is pretty far removed from a “Hello world” exercise, but maybe it’ll be fun enough to motivate you to learn more. The deeper you get into PowerShell, the more learning some C# might help you.

So, let’s get at it. First, clone the repository with git clone or fork it and clone your fork. Check out the contribution guide for information on how to prep your environment and build your own pwsh.exe from the source.

Then, open the PowerShell.sln file in Visual Studio, or open up the project in VS Code. I tend to prefer “full blown” Visual Studio for writing C#, because it’s what I’m used to, but VS Code is perfectly fine, with a couple extensions added on (which are recommended as soon as you start looking at C# stuff).

So, now, what do you want to do? I like to start simple. When you first launch pwsh.exe there’s a banner message that is displayed, which at the time of this writing reads something like:

PowerShell 6.1.0
Copyright (c) Microsoft Corporation. All rights reserved.
Type 'help' to get help.

Let’s make that more interesting. Probably, there’s a string somewhere that we can just edit and make it say whatever we want.

If you expand powershell-win-core, you’ll see Program.cs which is probably what gets run when you fire up pwsh.exe in Windows. At least, when I started poking around, that was my guess. It seems pretty simple. It returns an UnmanagedPSEntry.

Look at the definition of the UnmanagedPSEntry class (by right clicking on it and selecting “Go to definition”), and you can read the code for the Start() method that is called in Program.cs. Eventually, you’ll get to around line 70 in the file that defines UnmanagedPSEntry (at the time of this writing) where a variable named banner, and another one named formattedBanner are assigned a value. The banner value seems to come from another class called ManagedEntranceStrings so maybe let’s take a look at that. That name alone sort of sounds like the type of thing we want to mess with right now.

The ManagedEntranceStrings class which, as the comment in the file suggests, returns the cached ResourceManager instance used by the class. It looks like it’s located at "Microsoft.PowerShell.ConsoleHost.resources.ManagedEntranceStrings". So… let’s go peek in there. It’s a resx file.

Aha! Looks like maybe we found it. There’s a ShellBannerNonWindowsPowerShell item that looks like we can fudge around with. I’m just going to make it a little more casual.

Save everything, follow the above linked directions to build PowerShell, and launch the pwsh.exe that it created. You should see your new message. Mine looks like this.

Welcome to PowerShell 6.1.0. If you're stuck, type 'help', otherwise, check out the docs.

It’s the little things that add the most joy to life. In all honesty though, explore a bit and you’ll start to learn about how PowerShell really works, and next time you see something that doesn’t work like you think it should, you’ll have more power to do something about it.

Written on November 21, 2018