Re: [Help-bash] difference of $? and ${PIPESTATUS[0]}

[Chet Ramey]

On 4/22/24 2:13 AM, felix wrote:

> I could explain that '$?' is result of bash's if...then...fi group command
> executed correctly and PIPESTATUS hold result of "most-recently-executed
> foreground pipeline", but man page say:
>
>      PIPESTATUS
>           An  array  variable (see Arrays below) containing a list of exit
>           status values from the processes in  the  most-recently-executed
>           foreground pipeline (which may contain only a single command).
>
>       ?   Expands  to  the exit status of the most recently executed fore‐
>           ground pipeline.

It's clumsy wording, no doubt, but the two aren't intended to be the same
or necessarily have the same value.

The language in the description of $? is very close to POSIX, since the
POSIX grammar basically makes any command a pipeline. It's formal so the
standard can relate it to the grammar, but very few people think of

if a; then echo b; else echo c; fi

as a `pipeline'.


> If so, "$?" have to be equivalent to "${PIPESTATUS[0]}", I think.

No, even if this were true, it would be the last member of PIPESTATUS,
modulo the `pipefail' setting.

> I suggest that man page should be modified to replace "foreground pipeline"
> by "command" under "?" paragraph.

Yeah, that's probably closer to the real meaning. The description of
PIPESTATUS refers to pipelines as described in Pipelines under SHELL
GRAMMAR (which can also be a Simple Command from the same section).

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

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