On 9/1/21 4:59 PM, (Joerg Schilling) wrote:
"Chet Ramey via austin-group-l at The Open Group" 
<austin-group-l@opengroup.org> wrote:

Given the following:

(exit 42)
a=$? b=`false` b=$?

echo $? $a $b

Bash prints 1 42 1.

The original (v7) bourne shell and the rest of the research line through v9
prints 1 1 (b is set to the empty string). That implies that it executes
the assignment statements in reverse order, in addition to carrying $?
through the sequence of assignments.

You are right, the original Bourne Shell for unknown reasons did evaluate a
series of shell variable assignments in reverse order. That was changed in
ksh88 and in bosh.
The SVR4.2 shell prints 1 42 1. I imagine the rest of the SVR4 line sh is
the same.

Something called SVR4.2 does not really exist. It was a minor change compared
to SvR4 announced by Novell short before they sold the Copyright to SCO. >
I know of no customers for SVR4.2... even SCO seems to only used it internally
in their project Monterey that was abandoned by IBM.

And yet it existed as a product. Univel probably had Unixware customers
they didn't tell you about.

You can find it for download if you look for it, I suspect.

There have been major changes in the Bourne Shell for SvR4, but the $? was not
touched. So you are mistaken.

Sure, I didn't have SVR4 to test against when I wrote that.

The important thing to know here is that the Bourne Shell has some
checkpoints that update the intermediate value of $?. Since that changed in
ksh88 and since POSIX requires a different behavior compared to the Bourne
Shell, I modified one checkpoint in bosh to let it match POSIX.

Interesting, since ksh88 (Solaris 10 11/16/88i) and ksh93 (93u+ 2012-08-01)
both print

1 42 1

Odd that POSIX would specify something different, isn't it?


(exit 42); a=$? b=`false` b=$?; echo $? $a $b

prints

1 42 42

in bosh and

1 1

in the SvR4 Bourne Shell.

It echoes 255 255 with the Solaris 10 /bin/sh (b is again null). It looks
like /bin/false exits with status 255, the Solaris 10 sh still performs
the assignments in reverse order, and the Solaris 10 version of the SVR4 sh
sets $? from the result of each command substitution.

In any case, kre's point stands: the original Bourne shell (and, for that
matter, the POSIX base implementation) set $? as each command substitution
finishes.

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

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