Re: Inconsistent behavior of ERR_EXIT with conditionals

[Philippe Altherr <philippe.altherr@gmail.com>]

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>
> Neither of these is a situation where the developer should have been
> relying on errexit to save them.


My ultimate point with that example was to demonstrate that ERR_EXIT
doesn't achieve my goal.

My goal is to be able to run a Zsh script with the guarantee that if
anything goes wrong the script stops immediately where by "anything goes
wrong" I mean any command whose result is not otherwise checked returns a
non-zero exit status. If you don't agree that this would be a useful
feature, then we can stop the discussion.

If you think that ERR_EXIT achieves my goal, then it would be useful if you
could give me an example of a legitimate use of/reliance on ERR_EXIT. I
could then try to build a better example to demonstrate that ERR_EXIT is
not achieving my goal. If I fail to convince you that ERR_EXIT does not
achieve my goal, then too we can stop the discussion.

I would abstain from the decision and leave it to others, but I don't
> believe it can be done without some rather invasive changes.


Indeed, that remains an open question to me and I agree that the new option
shouldn't be added if it requires too much additional complexity.

Philippe


On Wed, Nov 9, 2022 at 7:00 AM Bart Schaefer <schaefer@brasslantern.com>
wrote:

> On Tue, Nov 8, 2022 at 8:11 PM Philippe Altherr
> <philippe.altherr@gmail.com> wrote:
> >>
> >> The first developer is wrong.  That's not what -e is for.  A script
> >> should be correct WITHOUT the use of -e ... the purpose of -e is to
> >> uncover cases where the developer made a mistake, not to be an
> >> integral part of the script function.
> >
> > I can agree with that but consider that the developer's mistake was to
> use a ";" instead of an "&&" in the "backup" function.
>
> No, that wasn't his mistake.  His mistake was to not explicitly call
> "exit" on failure of scp and instead rely on errexit to bail out of
> the backup function.
>
> The second developer's mistake was changing ; to && following the call
> to the backup function without actually understanding how the backup
> function (didn't) work.  *If* errexit worked the way you want, the &&
> test would be spurious anyway, because either the function would have
> returned the status of "echo" (always success) or would have died
> without getting that far.
>
> Neither of these is a situation where the developer should have been
> relying on errexit to save them.
>
> > My broader point was that the same error (or developer mistake) in a
> function "foo" triggers an exit if "foo" is called from a plain statement
> but not if it's called from within a condition. Wouldn't you agree that
> it's unfortunate that the same error/mistake may or may not trigger an exit
> depending on whether it's executed outside or inside a condition?
>
> I wouldn't necessarily agree that it's the same mistake.  What's
> unfortunate is that you're relying on a Deus ex machina to save your
> script from disaster.
>
> > Would you agree to add a new shell option if it allows to run Zsh
> scripts such that if any command unexpectedly fails the script immediately
> stops (and its implementation doesn't require too complex changes)?
>
> I would abstain from the decision and leave it to others, but I don't
> believe it can be done without some rather invasive changes.
>

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