Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Subscribe: <mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive: <http://sources.redhat.com/ml/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-help AT cygwin DOT com>, <http://sources.redhat.com/ml/#faqs>
Sender: cygwin-owner AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
Delivered-To: mailing list cygwin AT cygwin DOT com
X-envelope-info: <rschulz AT sonic DOT net>
Message-Id: <5.2.1.1.2.20030528062212.01f54ff8@pop.sonic.net>
X-Sender: rschulz AT pop DOT sonic DOT net
Date: Wed, 28 May 2003 06:30:47 -0700
To: cygwin AT cygwin DOT com
From: Randall R Schulz <rschulz AT sonic DOT net>
Subject: Re: behaviour of "for (( exp1; exp2; exp3 )); do COMMANDS;
  done"
In-Reply-To: <eq29dvgfdunpptfj4ak084g2lfa22as6m1@4ax.com>
References: <20030527120718 DOT GA22030 AT convex DOT org DOT uk>
 <002901c32427$2e1553e0$78d96f83 AT pomello>
 <PHENJGDFMJPEBOBLGEMOKENMCBAA DOT peter DOT oosterlynck AT oracle DOT com>
 <ocj6dvc16hc7e702hhe1dktohpm1306oi6 AT 4ax DOT com>
 <20030527120718 DOT GA22030 AT convex DOT org DOT uk>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"; format=flowed

Sam,

At 03:17 2003-05-28, Sam Edge wrote:
>Stuart Brady <stuart AT convex DOT org DOT uk> wrote in
><20030527120718 DOT GA22030 AT convex DOT org DOT uk>
>in gmane.os.cygwin on Tue, 27 May 2003 13:07:18 +0100:
>
> > On Tue, May 27, 2003 at 12:42:21PM +0100, Sam Edge wrote:
> > > Make sure that if your script uses Bash-specific features, it starts
> > > with #!/bin/bash and not with #!/bin/sh. That way it'll work anywhere.
> >
> > You've made the assumption that bash is always in /bin. I've seen it
> > in /bin, /usr/bin, /usr/local/bin, /usr/contrib/bin, and /opt/bash/bin.
> > ~/bin would be another likely place for it.
>
>I just _knew_ I shouldn't have said "anywhere." ;-)
>
>Unfortunately this is a general weakness in the "#!/xxxx" syntax.
>
>(OT) Does anyone know if any of the common shells, when they see
>"#!/bin/xxxx" at the front of a script, try a $PATH search for an
>"xxxx" executable if they can't find "/bin/xxxx"? This would seem like
>a good idea to me.

The interpretation of #! lines is in the kernel (or, hereabout, 
Cygwin1.dll, a kernel by any other name), just as the kernel would how 
to handle a binary executable by examining its header.

However, shells usually fall back to interpreting script if the kernel 
reports particular errors on the exec(2) system call (ENOEXEC, i.e.). 
When this happens, the shell knows that the file exists, that the 
permissions allow execution but the kernel could not execute the file 
because its format was not suitable. Then the shell will try to 
interpret the script as one of its own. (That, by the way, causes some 
odd errors when foreign executables are brought to Cygwin and executed. 
Cygwin1.dll and / or Windows cannot execute these so the shell starts 
interpreting a binary file as commands. Shell syntax errors ensue.)

So the shells could be modified to do what you suggest, but if there 
are any that do it now, I don't know of them, but I really only know 
much about BASH these days.

I seem to recall some discussion way back when as Berkeley Unix 
introduced this feature about PATH searching for #! executions being a 
possible security hole. To my knowledge, no Unix does this, but again, 
I claim no extensive knowledge of the current state of affairs.

Randall Schulz


>Regards,
>--
>Sam Edge


--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Problem reports:       http://cygwin.com/problems.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/