#! -- reconsideration?

Dan Kegel dank at alumni.caltech.edu
Tue May 9 13:54:49 PDT 2000

Don Cragun wrote:
>         I also like the simplicity of /bin/posixsh, but until we can
> guarantee that no future amendment or revision of a POSIX standard will
> ever place any incompatible requirements on "standard" utilities, this
> just won't work.  Implementations have to have a way to provide
> applications with a way to access a stable "environment" that won't
> change even when a new version of the standard is published.  The
> Solaris 8 Operating Environment currently supports applications written
> to lots of different specifications and standards (including, but not
> limited to: 4.3BSD, SVID3, XPG3, XPG4, SCD 2.4.1, SUS, SUSv2, and
> various versions of POSIX ... This is all done by choosing appropriate compiler
> flags and settings for the PATH environment variable consistent with
> the environment the application wants to use.  


>         The POSIX standards and the Single UNIX Specifications have
> wisely chosen not to specify hard coded pathnames for the standard
> utilities.  Implementations need to give users a description of how to
> find the set of utilities specified by the standards they support, and
> the standards need to specify how to find the rest of the standard
> utilities once you get to that point (such as Austin Group revision
> draft 3 XCU's
>                 getconf -v specification PATH
> command.)  Then applications that want to use #! have to be configured
> to find the absolute pathname for the utility they want invoked as the
> interpreter by #! as part of their installation processing.

So you're proposing that a package that wants to be portable will
rewrite all of its shell scripts at install time and replace the thing
following #! with the absolute path to the POSIX-compliant shell
located in the first directory listed in `getconf PATH`?

That's reasonable, I suppose, but it's not something I've seen done
in practice yet.  Has anyone else observed this in the wild?

Now that you've explained your objection to /bin/posixsh, can you
comment on /usr/posix/bin/sh?
- Dan

You didn't really mean that -v was a useful flag for our
purposes here, right?  -v is used to select machine word sizes
and the like, not to select Posix vs. xpg3 etc., according to 

Entia non sunt multiplicanda praeter necessitatem.

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