Re: Q on Bash's self-documented POSIX compliance...

[Clark WANG]

On Sat, Jan 26, 2013 at 1:27 PM, Linda Walsh <bash@tlinx.org> wrote:

> I noted on the bash man page that it says it will start in posix
> compliance mode when started as 'sh' (/bin/sh).
>
> What does that mean about bash extensions like arrays and
> use of [[]]?
>
> Those are currently not-POSIX (but due to both Bash and Ksh having
> them, some think that such features are part of POSIX now)...
>
> If you operate in POSIX compliance mode, what guarantee is there that
> you can take a script developed with bash, in POSIX compliance mode,
> and run it under another POSIX compliant shell?
>
> Is it such that Bash can run POSIX compliant scripts, BUT, cannot be
> (easily) used to develop such, as there is no way to tell it to
> only use POSIX?
>
> If someone runs in POSIX mode, should bash keep arbitrary bash-specific
> extensions enabled?
>
> I am wondering about the rational, but also note that some people believe
> they are running a POSIX compatible shell when they use /bin/sh, but would
> get rudely surprised is another less feature-full shell were dropped in
> as a replacement.
>

I think every POSIX compatible shell has its own extensions so there's no
guarantee that a script which works fine in shell A would still work in
shell B even if both A and B are POSIX compatible unless the script writer
only uses POSIX compatible features. Is there a pure POSIX shell without
adding any extensions?