Kind of off topic, but why in the world in 2026 do POSIX utilities still rely on global variables to pass around state? Is it too complicated to pass around a struct address in C or something?
You may also notice that some of these utilities will allocate memory, then never free it. They just let the OS handle that on program shutdown. That is also generally not recommended in arbitrary code. But again, it's fine for a one-and-done sort of program.
For these cases, the whole program is essentially one function call, and the global namespace is essentially the "body" of that function (hand waving a bit).
It's all a bit subjective, of course (:
Sure, in anything larger, or anything that needs to be reentrant, global variables are going to hurt. But this is not that.
The main issue with this is that the programs are usually still single-threaded. For some key utilities like find and grep, this has allowed more modern alternatives to leapfrog them in performance. (To be fair, it’s hard to add parallelism without breaking compatibility somewhat.)
But in most other respects, there’s nothing wrong with being a little old-fashioned. Using global variables is an example of that. It’s a problem in larger programs but at this scale it’s fine.
We'd prefer Rust versions with great forethought, but it's irrelevant to the testing.
There is no current version of Linux [uswrland] that maintains certified POSIX compliance. Only Apple, IBM, HP, and SCO are current?
It's a good rule of thumb to avoid them both, especially when you're inexperienced yet, but they still have their uses - as implied by it being a "rule of thumb".