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Re: ignoring current shell and always running posix shell? Re: Should th

From: Chet Ramey
Subject: Re: ignoring current shell and always running posix shell? Re: Should this be this way?
Date: Tue, 12 Mar 2013 10:36:17 -0400
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On 3/11/13 6:37 PM, Linda Walsh wrote:

>       It would make no sense for posix to take the stance that any
> unknown script without a shebang at the top, presented to any interpreter 
> shell
> be ignored by the interpreter and instead shall be run under /bin/sh.

The Posix shell specification only talks about the Posix shell.  Likewise,
Posix takes no position on whether or not shells offer extensions beyond
the Posix-specified functionality.

There are no other Posix interpreters (well, ok, there's awk).  The
likelihood of users attempting to run a script written in an arbitrary
non-shell language without a #! from the shell prompt is quite small, so
it's reasonable for the standard to contain what it does.  The standard
attempts to codify existing historical practice.

>       Posix used to claim they were "descriptive", not "prescriptive", though
> they are becoming more of the latter with each new update, I'd find it hard to
> think they'd try to enforce all script languages to default sources to 
> /bin/sh.

You're entitled to your opinion.  The fact remains, though, that this same
language, or something very similar, has been in the Posix standard since
1992.  As I said above, it attempts to standardize historical practice.

The default bash behavior and the SuSE modification are both conformant.

The more interesting question is why SuSE feels the need to do this.  The
original bug report from five years ago admits that it's not a solution to
the underlying SuSE-specific problem, just a workaround.  Subseqent
comments admit that the problem has been fixed for quite a while, but "may
reappear at any time."  I find this unconvincing, but it's not the first
time a vendor has changed bash, not documented the result, and declined to
revisit the decision.


``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/

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