Re: POSIXLY_CORRECT not correctly unset in getopt.m4?

[Eric Blake]

[adding bug-standards, regarding whether env is portable]

On 09/07/2010 12:11 PM, Dustin J. Mitchell wrote:
> There's no outer macro that does this, it's just the shell:
>
> bash$ echo $POSIXLY_CORRECT
>
> bash$ /bin/sh -c 'echo $POSIXLY_CORRECT'
> y
> bash$ /bin/sh -c '/usr/bin/env' | grep POSIXLY

Aha - bash itself is setting POSIXLY_CORRECT as a local variable upon 
'set -o posix'; and /bin/sh (as bash) runs with 'set -o posix' already 
specified.

$ bash -c 'set -o posix; echo ${POSIXLY_CORRECT:+set}'
set

> I like the approach in this patch, but sadly it doesn't work.
>
> This line:
> +       case ${POSIXLY_CORRECT:+x}`/bin/sh -c 'echo ${POSIXLY_CORRECT:+x}'` in
> does not do what you want, because the /bin/sh in the `` will re-set
> POSIXLY_CORRECT.

Oh, yeah (I did say minimally-tested ;)

> I've been using `env | grep POSIXLY_CORRECT` to check,

Hmm, env is required by POSIX, but it is not (yet) listed in the list of 
programs safe to use in GNU Coding Standards:

http://www.gnu.org/software/automake/manual/standards.html#Utilities-in-Makefiles

> locally, but I don't think 'env' is very portable -- and it's probably
> sometimes implemented as a shell builtin, which would defeat the
> purpose.

Nah - even if env is a shell builtin (any example of a shell that does 
that, by the way?), it would still have to obey POSIX rules.

> Also, your comment says "Some people", as if this were some oddball
> configuration this freaky Dustin guy is asking you to support.  This
> is not my doing.

Yeah, I agree that this is a more widespread issue - autoconf itself 
forces bash into POSIX mode (even when not invoked as /bin/sh), because 
it is just impossible to guarantee portability otherwise.  Which does 
indeed mean that POSIXLY_CORRECT will _always_ appear as set when 
running under bash, whether or not it is exported.

Any other ideas for portable ways of detecting whether a shell variable 
is currently local-only or exported?

--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org