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

A shell in Rust could be really cool

Posted Feb 17, 2025 13:42 UTC (Mon) by taladar (subscriber, #68407)
In reply to: A shell in Rust could be really cool by himi
Parent article: Rewriting essential Linux packages in Rust

You get exactly that error but if you e.g. write a script in e.g. March and test it only with dates occurring while you write it (and maybe 01 and 12 for over/underflow edge cases) you can easily end up with a script that breaks with that error in August or September (month 08 and 09).

The solution is easy once you know about it, you can simply prefix every variable in the arithmetic expression with 10# to force base 10 but you need to know about.

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A shell in Rust could be really cool

Posted Feb 18, 2025 21:46 UTC (Tue) by himi (subscriber, #340) [Link]

Ah, thanks for that explanation, it makes sense, and adds one more thing to the list of gotchas for me to keep in mind with shell code . . .

I try to use unix timestamps ($(date +%s)) whenever I'm dealing with times and dates of any sort in shell scripts, and then use $(date -d @...) to convert to something human readable - not particularly portable, but I'm fortunate enough to only really deal with Linux systems (aside from an occasional Mac, which has caused me serious headaches at times).

I do sometimes use sub-second precision (e.g. $(date +%s.%N)) for higher resolution timing, which then necessitates using bc -l or similar for any calculations. That recently bit me, in combination with scoping issues - I was mixing second and sub-second precision and the (perfectly logical) variable name 'now', and getting errors from arithmetic expansions when a sub-second precision value was still active where I thought it should be second precision . . . Fixing that just required fixing the scoping and naming issues ('local' is one of my favourite keywords), but it took *far* to long to spot the bug.

And to bring this back on topic, that's one monstrosity of a shell script that *absolutely* needs to be rewritten - though probably not in Rust, sadly, since I'm the only person in my team who'd have any hope of working on a Rust version . . .