A shell in Rust could be really cool [LWN.net]

A shell in Rust could be really cool

Posted Feb 13, 2025 6:01 UTC (Thu) by marcH (subscriber, #57642)
In reply to: A shell in Rust could be really cool by dskoll
Parent article: Rewriting essential Linux packages in Rust

No shell script should be longer than some number of lines and that threshold is... "it depends" but it's always longer than 15 lines....

Error handling is a real pain in shell (just like in... C) but "set -e" and "trap EXIT" mitigate a bit.

The truth is: the shell ability to "glue" processes, files and pipes is still unmatched. Why? Simply because that's exactly why it was designed for. Everyone who has ever used Python's "subprocess" knows that. Also, "shellcheck" is incredibly good; saved me hours and hours of code reviews thanks to: "please run shellcheck, it will tell you what's wrong with this line". Last but not least: the shell is a decent... functional language! You can put a function in a variable which is amazing and very useful for a language that limited otherwise.

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A shell in Rust could be really cool

Posted Feb 13, 2025 7:13 UTC (Thu) by himi (subscriber, #340) [Link] (7 responses)

> Also, "shellcheck" is incredibly good; saved me hours and hours of code reviews thanks to: "please run shellcheck, it will tell you what's wrong with this line".

I would like to second, third and fourth this (and then some) - shellcheck is amazing, it makes creating maintainable code in shell massively more practical.

The biggest issue I have with shellcheck is actually that it's /too/ good - it dramatically raises the threshold where my gut starts screaming at me that it's essential to rewrite this thing (some random hack grown into a monstrosity) in a "real" language, leaving me with constant cost/benefit anxiety. I've caught myself more times than I'd like to admit thinking "This really needs to be redone in Python . . . . but the incremental cost of adding X feature to the shell code is less than the cost of completely rewriting 1000+ lines of shell code from scratch, so . . . "

Without shellcheck making such a massive improvement in the quality, consistency and coherence of my shell code that would never have become a thing for me - it truly is both a blessing and a curse.

A shell in Rust could be really cool

Posted Feb 13, 2025 9:11 UTC (Thu) by taladar (subscriber, #68407) [Link] (6 responses)

I will never understand why people even consider Python when rewriting a shell script considering shell runs basically everywhere and any given Python version runs basically nowhere in terms of distros over time.

A shell in Rust could be really cool

Posted Feb 13, 2025 10:01 UTC (Thu) by NYKevin (subscriber, #129325) [Link] (1 responses)

Because I don't need my quick and dirty script to run everywhere. I need it to run on the one system that is sitting right in front of me. That system has a reasonably recent Python, and Python is far less painful to program in than bash or other shells, so I will write scripts in Python.

A shell in Rust could be really cool

Posted Feb 13, 2025 12:48 UTC (Thu) by pizza (subscriber, #46) [Link]

> Because I don't need my quick and dirty script to run everywhere.

"It's only temporary if it doesn't work"

A shell in Rust could be really cool

Posted Feb 13, 2025 12:48 UTC (Thu) by pizza (subscriber, #46) [Link]

> I will never understand why people even consider Python when rewriting a shell script considering shell runs basically everywhere and any given Python version runs basically nowhere in terms of distros over time.

...And given how perl goes through great pains to be "bugward" compatible indefinitely.

(I have literally decades-old perl scripts that still JustWork(tm). During the python2->python3 migration debacle I decided to just rewrite a lot of p2 (and early p3) into perl instead, and it's not needed to be touched since then. Ran faster, too)

A shell in Rust could be really cool

Posted Feb 13, 2025 18:43 UTC (Thu) by Cyberax (✭ supporter ✭, #52523) [Link]

If you just stick to the built-in Python library (subprocess and the general IO), then you can get reasonable coverage across modern distros.

A shell in Rust could be really cool

Posted Feb 13, 2025 22:53 UTC (Thu) by himi (subscriber, #340) [Link] (1 responses)

Because my quick and dirty hack that grew into a thousand line monstrosity isn't portable? Either in the sense of the tooling and configuration it uses, or in applicability.

It may have been moderately portable when it really was a quick hack, but even then it was probably only used in exactly one location and probably wasn't very useful anywhere else. The growth pattern that turned it into a monstrosity certainly didn't increase portability - it made it into something with even more detailed ties to the environment it's used in.

Shell /is/ good for quick and dirty hacks that are moderately portable, far better than Python. But quick and dirty hacks tend to keep getting hacked on, and the point of the whole thread here is where you stop hacking on the shell code and rewrite it in something that's a bit more amenable to proper software engineering practises . . .

A shell in Rust could be really cool

Posted Feb 14, 2025 2:05 UTC (Fri) by marcH (subscriber, #57642) [Link]

> But quick and dirty hacks tend to keep getting hacked on, and the point of the whole thread here is where you stop hacking on the shell code and rewrite it in something that's a bit more amenable to proper software engineering practises . . .

Note this is not so specific to shell. How many times have we looked at some piece of code and thought "This has grown organically, it should really be rewritten". Of course the bar tends to be much higher when a language switch is required, notably because the _incremental_ change possibilities are much more limited. But at a very high level it's the same https://wiki.c2.com/?PlanToThrowOneAway logic.