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Re: Bug when using pipefail and lastpipe together in bash-4.4


From: Chet Ramey
Subject: Re: Bug when using pipefail and lastpipe together in bash-4.4
Date: Fri, 11 Oct 2019 11:48:36 -0400
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.9.0

On 10/8/19 9:43 AM, Webstrand wrote:
> When running the following script under bash-4.4.0 to bash-4.4.23 it
> seems to fail erroneously on read.
> 
>   set -x
>   set -o pipefail
>   shopt -s lastpipe
> 
>   main() {
>     # Any input piped into while such that the condition
>     # succeeds at least once.
>     echo "x" | while read; do
>       echo | read # anything piped to read
>       sleep 0     # any non-builtin
>     done
>   }
> 
>   main || echo "main failed"
> 
> This produces the xtrace:
> 
>   + set -o pipefail
>   + shopt -s lastpipe
>   + main
>   + read
>   + echo x
>   + read
>   + echo
>   + sleep 0
>   + read
>   + echo 'main failed'
>   main failed
> 
> Under bash-4.3 and bash-5.0 the script does not output "main failed",
> as expected.
> 
> I'm not sure if this is a known bug. One user on IRC reported finding
> the same issue on debian stretch, but another could not reproduce the
> issue for bash-4.4.12.
> 
> I have bisected the history of the devel git branch and found that the commit:
>   85ec0778f9d778e1820fb8c0e3e996f2d1103b45 commit bash-20150417 snapshot
> introduces the issue.
> 
> Applying the attached patch to a bash-4.4.23 source tree produces an
> interpreter which does not output "main failed" when running the
> aforementioned script.

It's pretty clear that that patch is not the determining factor, since that
code exists in bash-5.0 and the problem doesn't occur.

The actual fix probably came in in the bash-20180817 snapshot, as a result
of

https://savannah.gnu.org/support/index.php?109541


-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    address@hidden    http://tiswww.cwru.edu/~chet/



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