Subject: Re: [PATCH v2] CodingGuidelines: document a shell that "fails" "VAR=VAL shell_func"

From: Junio C Hamano <[email-masked]>
Date: Tue, 23 Jul 2024 08:28:27 -0700

Jeff King <[email-masked]> writes:

> On Mon, Jul 22, 2024 at 04:10:41PM -0700, Junio C Hamano wrote:
>
>> Over the years, we accumulated the community wisdom to avoid the
>> common "one-short export" construct for shell functions, but seem to
>> have lost on which exact platform it is known to fail.  Now during
>> an investigation on a breakage for a recent topic, we found one
>> example of failing shell.  Let's document that.
>
> My recollection was that FreeBSD's /bin/sh was the culprit, but I
> couldn't find any mention digging in the archive. However, I just
> checked on a FreeBSD 13 VM, and it does have the same problem (that the
> one-shot variable is not exported). I don't think that changes anything
> for your patch, but just reinforces this part:
>
>> This does *not* mean that we can freely start using the construct
>> once Ubuntu 20.04 is retired.  But it does mean that we cannot use
>> the construct until Ubuntu 20.04 is fully retired from the machines
>> that matter.
>
> since now we have one other instance.
>
> I thought it also had the issue that the variable would remain set in
> the caller after the function returned, but it does not seem to do so
> now (if it ever did).

Yeah, that one is also what POSIX leaves to the implementation, if I
recall what I read there.

So here is how the part looks like in my tree right now.  

Thanks.

diff --git c/Documentation/CodingGuidelines w/Documentation/CodingGuidelines
index 2151ec51b8..52afb2725f 100644
--- c/Documentation/CodingGuidelines
+++ w/Documentation/CodingGuidelines
@@ -212,11 +212,11 @@ For shell scripts specifically (not exhaustive):
    "command args" is running is handy, but this triggers an
    unspecified behaviour according to POSIX when used for a command
    that is not an external command (like shell functions).  Indeed,
-   some versions of dash (like 0.5.10.2-6 found on Ubuntu 20.04) and
-   AT&T ksh do make a temporary assignment without exporting the
-   variable, in such a case.  Do not use it for shell functions.  A
-   common workaround is to do an explicit export in a subshell, like
-   so:
+   dash 0.5.10.2-6 on Ubuntu 20.04, /bin/sh on FreeBSD 13, and AT&T
+   ksh all make a temporary assignment without exporting the variable,
+   in such a case.  As it does not work portably across shells, do not
+   use this syntax for shell functions.  A common workaround is to do
+   an explicit export in a subshell, like so:
 
 	(incorrect)
 	VAR=VAL func args