Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!usenet.ins.cwru.edu!ncoast!allbery
From: allbery@NCoast.ORG (Brandon S. Allbery KB8JRR)
Newsgroups: comp.unix.shell
Subject: Re: the #! notation
Message-ID: <1991Jan23.044019.4807@NCoast.ORG>
Date: 23 Jan 91 04:40:19 GMT
References: <1991Jan21.174803.6661@mp.cs.niu.edu> <16209@burdvax.PRC.Unisys.COM> <587@fciva.FRANKCAP.COM>
Reply-To: allbery@ncoast.ORG (Brandon S. Allbery KB8JRR)
Followup-To: comp.unix.shell
Distribution: na
Organization: North Coast Computer Resources (ncoast)
Lines: 25

As quoted from <587@fciva.FRANKCAP.COM> by dag@fciva.FRANKCAP.COM (Daniel A. Graifer):
+---------------
| Perhaps I've missed something here, but none of this #! stuff works on my
| machine (running Sys V/386 3.1).  Is this something that only works in 
| BSD-derived unixes?  What about V3.2 or V4?
+---------------

It's a BSD-ism (and requires some kernel hacks to implement).  It also
includes the seeds of a security hole --- if you've ever read any messages on
the net about "disabling setuid shell scripts", the #! mechanism is both what
makes setuid shell scripts possible and what makes them insecure.

Note that some shells can emulate this mechanism when the kernel doesn't
support it --- I think bash does, for instance, and I have posted my "bexec"
mechanism for making any System V csh do so many times.  (I will *not* repost
it here yet again; if anyone wants it, send me mail.  But considering the
number of times I've posted it in the past, it ought to be archived all over
the net by now.)

++Brandon
-- 
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