So, if I were trying to write my own implementation of a fully bash-compatible UNIX shell, what standards and/or functionalities should I be aware of, and where would I look for the best information?

Also, would there be any perceived downside to using a language other than C? Perhaps Go or Rust?
I have no problem with C. In fact, I'm most familiar with it. But I'm curious about the implications of the use of other languages in building such system utilities, and how it might affect development as well as the end-user's experience.

Recommend you look at the standard and/or functionalities in existing shell languages to begin your list of requirements, and then add/remove things where you determine there can be enhancements/benefits.I don't know Go or Rust really well. Rust is focused on safety, or that was it's intent, it is C++ derived. Go was invented at Google, I don't care to necessarily eschew something because it came from a certain place.

But like you:However I'm less this:Primarily because I've used C#, Objective-C, meaning various platform languages for specific things like Apple or Microsoft.

A language is a language. Add it to the pile.

I decided to use those native languages in their native environments because I tried programming for Windows using other libraries and there were technology gaps that I was endlessly working through. While there were numerous quirks using their native tools, they only stood in my way, by way of obscurity versus stood in my way because they didn't have support for something. Sorry I don't know if that makes much sense, but in all honesty Qt was great, but when I tried to access the user's root drive and home location or seek what types and how many serial ports there were on a system, it was jumping through a flaming hoop, doing a back flip. Not that MSVC was all that big of a picnic, but there's (exaggerating) 80 ways to access a serial port in there, so that's the over-problem sometimes with their native tools. Which way is right?

if you want to implement a bash compatible shell you need to check its source code (and documentation).

I'm just curious is there are any specific standards used by bash (Perhaps there are some POSIX standards or something used by UNIX shells that I should be aware of).
I don't intend to remove any bash functionality. Thinking more of a drop in replacement for bash with added functionality.

As far as I'm aware Go also puts emphasis on safety while also including functionality intended to make parallelization much easier, which I imagine might come in handy when writing something like a shell. It's goal seems to be safe and easy parallel processing while keeping things as fast as possible.
Rust seems to focus more on trying to act as a replacement for C/C++ with the advantage of added safety. So, as fast as possible, with all the low-level functionality you might need.

I've been meaning to learn more languages. Seems no one in Denver cares about C programmers, and knowing more languages is just generally useful. Having an excuse would be a good incentive.

I'm not really aiming for a source clone. I really just need to copy it's functionality.
I'm fine with checking the code for ideas on implementing functionality if I'm stuck, but for the most part, I just need a detailed look at how it acts under given circumstances.
Copying the functionality isn't too hard. I just want to know that I'm not overlooking anything (Both in syntax, and in how the shell interacts with the OS).

I guess I'm just looking for anything specifically giving a standard for the bash style syntax, or for the behaviour of the shell in a POSIX environment? Even some generally accepted rules for shell implementation would be nice.

Probably best to start with the POSIX XCU and Korn Shell documentation. Most shells are derived from them, including bash.

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Dual answer (1) none that I'm aware of, (2) bash uses the benefits of regex, but I believe python does the same.Then stick with bash.I can agree that "being capable of contending with other languages" has helped me, but I've been using C for 30+ years and currently use exactly that. I work with a great deal of developers in Boulder who program in C. I think really it boils down to the market where you work and seek work. For me it has always been embedded development.

If you want to understand how does bash work you may need to check the source code. I don't meant to copy it. Just to understand. Bash itself it relatively complex.
From the other hand you may try the tests written for bash and you can test your own shell (if it passes too).

FWIW, Microsoft says that the source code for the original Bourne shell is particularly bad.

A rant against flow control macros

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Here are a few tutorials that came up in a web search:

• Tutorial - Write a Shell in C
• Writing a Unix Shell - Part I
• Making your own Linux Shell in C
• Writing a simple shell in Go
• EnthusiastiCon - Stefanie Schirmer “OMG building a shell in 10 minutes”
• Build Your Own Shell using Rust
• Building a Shell - Part 1

As for the language: you're probably going to to use readline to take input and fork/exec to launch programs. You can use any language that gives you access to those. There are no real technical considerations (to the language choice) apart from that.

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That example is indeed truly horrid, so I'll let the irony of someone at Microsoft complaining about bad code, slide.

I hate MACROS with a passion.

Mind you, Raymond Chen is not equals to Microsoft: the former is a person, the latter is a company.

The XCU is exactly the sort of thing I was looking for!
I knew there had to be something in the POSIX specification. I just wasn't sure where to look.
Actually the entire XCU looks like it would be generally useful to have.

And after only 650 pages my printer now sounds like some dying animal begging for someone to end its suffering.

I wonder if it would be possible to write a shell in a high level scripting language like, say, bash?
I guess one would have to take care to actually re-implement every bit of it, not just pass it through...

There's a shell written in Python...

https://www.oilshell.org/

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