Re: PIPESTATUS differs from $? for compound command

[Dale R. Worley]

My opinions on this subject:

It's probably not worth changing the behavior, particularly since there
is likely to be some small amount of code out there that depends on it.

The behavior in regard to ! is correct (as has been noted) because
PIPESTATUS records the values of the commands in the pipeline, not of
the pipeline as a whole.

Someone noted that "! true | ! true" is a syntax error, which matches
the documentation.

Chet Ramey <chet.ramey@case.edu> writes:
> Compound commands don't generally set PIPESTATUS. Multi-element pipelines
> (the original purpose, because otherwise why bother), simple commands
> (single-element pipelines) including shell builtins, and compound commands
> that resemble simple commands (`[[', `((') set it.
>
> Yes, you can make the case that compound commands are pipelines, and,
> according to the grammar, they are, but their status is always available
> in $?, and they never have more than one status value.

The documentation is (as of 5.1):

       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).

This needs to be modified to note that compound commands that are not
one component of a multi-command pipeline do not cound as pipelines
for setting PIPESTATUS.  Exactly which compounds commands don't set
PIPESTATUS is not obvious.  E.g. "{...}" does not but "(...)" does.

"processes" should probably be changed to "commands" as that's what
they're called in the documentation.

"most-recently-executed foreground pipeline" should be clarified as
"most-recently-completed foreground pipeline".

Dale