Re: PIPESTATUS differs from $? for compound command

[Ulrich Müller]

>>>>> On Tue, 10 Dec 2024, Greg Wooledge wrote:

> My own testing:

> hobbit:~$ if true; then (exit 11) | cat; fi
> hobbit:~$ echo "$? ${PIPESTATUS[*]}"
> 0 11 0

> hobbit:~$ if true; then (exit 11) | cat; fi | false
> hobbit:~$ echo "$? ${PIPESTATUS[*]}"
> 1 0 1

> hobbit:~$ while (exit 12); do :; done
> hobbit:~$ echo "$? ${PIPESTATUS[*]}"
> 0 12

> hobbit:~$ true | while (exit 12); do :; done
> hobbit:~$ echo "$? ${PIPESTATUS[*]}"
> 0 0 0


> Given all that we've tried here, all I can determine is:

> 1) If an "if", "case" or "while" (and probably "until" too) is executed
>    by itself as the sole command in a pipeline, the compound command sets
>    the value of $? but not the value of PIPESTATUS.  It doesn't matter
>    whether the "body" is entered.

> 2) If the same command appears as part of a pipeline with other commands
>    in it, then the compound command's exit status does become part of
>    PIPESTATUS.

Yes, this seems to be a reasonable conclusion.

> It's hard to see how this is anything other than a bug.  But it's an
> incredibly long-standing behavior -- all the way back to 2.05b or
> earlier.  Given that PIPESTATUS is a bash extension, not part of POSIX,
> it's up to Chet to decide what to do about it.

Maybe looking at another shell is also useful?

With mksh 59c and your above examples, I get:

mksh $ if true; then (exit 11) | cat; fi
mksh $ echo "$? ${PIPESTATUS[*]}"
0 11 0

mksh $ if true; then (exit 11) | cat; fi | false
mksh $ echo "$? ${PIPESTATUS[*]}"
1 0 1

mksh $ while (exit 12); do :; done
mksh $ echo "$? ${PIPESTATUS[*]}"
0 0

mksh $ true | while (exit 12); do :; done
mksh $ echo "$? ${PIPESTATUS[*]}"
0 0 0

Also, for my previously reported test cases:

mksh $ if false; then :; fi
mksh $ echo "ret = $?, status = ${PIPESTATUS[*]}"
ret = 0, status = 0

mksh $ true; case a in esac
mksh $ echo "ret = $?, status = ${PIPESTATUS[*]}"
ret = 0, status = 0

mksh $ false; case a in esac
mksh $ echo "ret = $?, status = ${PIPESTATUS[*]}"
ret = 0, status = 0

All these results are what I would (naively?) expect them to be.