How should we deal with actual hush odd behavior?

[Francis Laniel]

Hi.


I hope you are fine and the same for your family and friends.

In July, a proposal to add a new shell for U-Boot was posted on the mailing 
list [1].
The community discussed a lot about this changes, some people did not agree 
with it because the new shell is not compatible with the actual one (hush) 
[2].
So, a proposal to update U-Boot actual hush to follow what they currently have 
in Busybox was made [3].

Porting 2021 Busybox hush to U-Boot seems, for me, to be a good idea as we 
would benefit from Busybox bug fixes as well as being compatible with actual 
hush (in theory).
We could also add new features to U-Boot hush, like functions, as they were 
added to Busybox.

Nonetheless, the idea of this port is to be compatible.
In practice, I noted some cases when this is actually not the case.
The first one can be related to how && and || operators were handled in hush.
So, the following: false && false || true
Returns 0 on Busybox 2021 hush and 1 on U-Boot.
The behavior of 2021 is coherent with the definition of these operators [4]:
>    The return status of AND and OR lists is the exit 
>    status of the last command executed in the list.
An other example concerns variable expansion, where foo='bar "quux" is 
expanded to bar quux in U-Boot and bar "quux in Busybox.

I do not have a real opinion on the second one, as I think local variable set 
in U-Boot scripts are quite simple as people do not try to do: foo="bar \"quux 
'quuz' \"\"\"corge".
The first one is maybe more problematic.
Grepping "if test" shows me that the more complex if condition seems to be 
under the form:
if first_test_ AND/OR second_test
Here also, people seems to no try to write complex expression like: foo || 
bar; echo quux && quuz.

So, porting Busybox 2021 hush can solve bugs we have currently in U-Boot, but 
what if fixing these bugs lead to a board script failing and so a device not 
booting...
I would like to have the opinion of the community on this question.


Best regards.

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[1] https://lists.denx.de/pipermail/u-boot/2021-July/453347.html
[2] https://lists.denx.de/pipermail/u-boot/2021-July/453790.html
[3] https://lists.denx.de/pipermail/u-boot/2021-July/453848.html
[4] https://linux.die.net/man/1/bash