changed exit code for 'dc' in Ubuntu Bionic

same is reproduced when you run 'dc', enter into it some expression ending with 'p q', and examining its exit code with 'echo $?' afterwards

Hi Wladimir,

Wladimir Mutel wrote:
> in Ubuntu Xenial :
> $ lsb_release -rdc ; echo 1 1 + p q | dc ; echo $?
> Description: Ubuntu 16.04.4 LTS
> Release: 16.04
> Codename: xenial
> 2
> 0
>
> in Ubuntu Bionic :
> $ lsb_release -rdc ; echo 1 1 + p q | dc ; echo $?
> Description: Ubuntu 18.04.1 LTS
> Release: 18.04
> Codename: bionic
> 2
> 1
>
> This change causes some scripts using 'dc' to fail, most importantly,
> 'dphys-swapfile'

Thanks for that bug report. This might be the cause for
https://bugs.debian.org/906767 which I'm currently trying to fix.

> which for some ironic reason uses 'dc' instead of 'echo
> $((...))' for its calculations.

That's upstream's decision. And since I know that upstream also runs
rather old Unices, I assume it's because $(( ... )) might not be
available in all shells. According to
https://en.wikipedia.org/wiki/Comparison_of_command_shells#cite_ref-57
it should though be available in all relevant shells since 1992.

The relevant change in dc seems to be from 1.3 to 1.4:

    Detects and reports on any output errors; exits non-success.

The fix seems simple: Drop the "q":

~ → echo 1 1 + p q | dc ; echo $?
2
1
~ → echo 1 1 + p | dc ; echo $?
2
0

Will have to check if that's indeed the cause for
https://bugs.debian.org/906767, but will do a new upload to Debian
Unstable in either case.

Someone else will need to take care of a regression fix for bionic
though.

  Regards, Axel
--
 ,''`. | Axel Beckert <email address hidden>, https://people.debian.org/~abe/
: :' : | Debian Developer, ftp.ch.debian.org Admin
`. `' | 4096R: 2517 B724 C5F6 CA99 5329 6E61 2FF9 CD59 6126 16B5
  `- | 1024D: F067 EA27 26B9 C3FC 1486 202E C09E 1D89 9593 0EDE

This bug was fixed in the package dphys-swapfile - 20100506-5

---------------
dphys-swapfile (20100506-5) unstable; urgency=high

  * Add patch to fix the setup subcommand exiting prematurely with more
    recent dc versions. (Closes: #906767, LP: #1788681) Also update
    check-diskspace-first.patch which uses the same syntax. Thanks to
    eHenry Berg for the initial bug report, Davide Prina for additional
    debugging help, and Wladimir Mutel for finding the actual culprit.

 -- Axel Beckert <email address hidden> Thu, 23 Aug 2018 23:29:41 +0200

Status changed to 'Confirmed' because the bug affects multiple users.

Fix has only been released for Cosmic. Given the package is basically non-functional on Bionic, is there a plan to backport the fix? There doesn't seem much point in keeping it in the repository otherwise.

4 years passed, no movements detected in Bionic ...

Holy necromancy! Is this still a bug? Is this affecting latest LTS 22.04?

$ lsb_release -rdc ; echo 1 1 + p q | dc ; echo $?
Description: Ubuntu 22.04.1 LTS
Release: 22.04
Codename: jammy
2
1

The bug is not in bc/dc (which documented their change of behavior).
It is in dphys-swapfile script which used to exit 'dc' by 'q' command.
The proper fix, in my view, would still be to use arithmetic substitution $((...)) provided by most modern shells, and make dphys-swapfile independent from 'dc' at all.