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

From: Pierre Gaston
Subject: Re: Q on Bash's self-documented POSIX compliance...
Date: Sun, 27 Jan 2013 10:22:35 +0200

On Sun, Jan 27, 2013 at 5:52 AM, John Kearney <address@hidden> wrote:
> Am 27.01.2013 01:37, schrieb Clark WANG:
>> On Sat, Jan 26, 2013 at 1:27 PM, Linda Walsh <address@hidden> 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?
> dash is normally a better gauge of how portable your script is, than
> bash in posix mode.

It is, but it still has a couple of extensions over the standard
There's also posh around.

As for the rationale, making it strictly compatible in order to test
scripts probably requires quite some more work and I bet Chet would
not be against a --lint option or something like that but it may not
be his primary objective.

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