Python surpasses Perl in popularity?

Andre Majorel cheney at halliburton.com
Mon Dec 1 11:16:36 CET 2008


On 2008-11-30, Stephane Chazelas <stephane.chazelas at unicyclist.com> wrote:
> 2008-11-30, 06:11(+00), Tam Ha:
>> Stephane CHAZELAS wrote:
>>> There's a common confusion in this in the nature of /bin/sh.
>>> There's no standard (neither POSIX nor Unix) that specifies that
>>> /bin/sh should be any variant of the Bourne shell.
>>
>> Sure there is, POSIX.
> [...]
>
> And on this. First, POSIX has no juridiction on defining the
> Bourne shell, let alone its location as the Bourne shell is
> completely outside POSIX, it's a legacy shell and as been for
> years. Then, POSIX makes it clear that the location of its sh
> utility (again, which the Bourne shell is not) is unspecified,
> only that the lookup of "sh" via $PATH in a conformant
> environment should resolve to a conformant "sh".
>
> And if you need some examples to be convinced, see the different
> choices of those 4 different POSIX conformant Unices:
>
> Solaris (7, 8, 9 at least):
>   /bin/sh: legacy Bourne/SVr4 shell
>   /usr/xpg4/bin/sh: a POSIX compliant shell (actually ksh88)
>   Solaris choice was to keep /bin/sh as the Bourne shell for
>   backward compatibility (as changing it for a POSIX shell
>   introduces a slight chance of breaking some existing scripts
>   as there are a few corner-case areas where the POSIX shells
>   are not backward compatible with the Bourne shell), and make
>   /bin a non standard place. How to get a conformant environment
>   (typically one where /usr/xpg4/bin/sh is before /bin) is
>   described in standards(5). The default one is not, which makes
>   Solaris a pain when porting scripts.
>
> HPUX (10.10 and newer at least):
>   /usr/bin/sh (and /bin/sh if there's a symlink /bin ->
>   usr/bin): a POSIX compliant shell (based on ksh88)
>
>   /usr/old/bin/sh: the Bourne shell (though I think nowadays,
>   it's part of an optional package).
>
> Tru64:
>   /bin/sh can behave either as a Bourne shell or a POSIX shell
>   (ksh88) depending on the environment

How does it decide ? argv[0] ? isatty (STDIN_FILENO) ?

> most Linux based systems and most other Unices:
>   /bin/sh is a POSIX compliant shell (bash generally for Linux)
>   and there's no Bourne shell (either there has never been or it
>   has been removed/replaced by a POSIX shell).

Two other Unixen I know of that have a non-POSIX sh are SCO Open
Server and UnixWare. I'm not sure they even provide a
POSIX-compliant alternative like Solaris does.

On the other hand, their utilities (awk, grep, sed et al.) seem
to be POSIX-compliant, at least to the extent that I've always
managed. Unlike Solaris where I've often had to use the ones in
/usr/xpg4/bin.

Many people assume "standard" equates "portable". As far as
shell programming is concerned, the safest way to get portability
is to ignore the standard and code for the Bourne shell.

-- 
André Majorel <URL:http://www.teaser.fr/~amajorel/>
"After 15 minutes, I wanted to marry her. After a half hour, I completely
gave up the idea of snatching her purse." -- _Take the Money and Run_



More information about the Python-list mailing list