From owner-freebsd-current  Sat Feb 20 12:16:38 1999
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Date: Sat, 20 Feb 1999 15:13:56 -0500 (EST)
From: Brian Feldman <green@unixhelp.org>
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To: Rahul Dhesi <dhesi@rahul.net>
Cc: current@FreeBSD.ORG
Subject: Re: sh(1) -- exec vs. fork 
In-Reply-To: <199902200258.AA26119@waltz.rahul.net>
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On Fri, 19 Feb 1999, Rahul Dhesi wrote:

> Many years ago I posted a shell script to Usenet in which I prepended a
> line with 'exec', in an attempt to avoid having a shell process hanging
> around doing a wait().  David Korn himself (of Korn shell fame)
> responded saying this was not necessary, as the shell would do exec()
> anyway.
> 
> I check with trace() on a Sun and he seemed to be right.  This was for
> the classic Bourne shell many years ago.
> 
> But I just checked /bin/sh on 3.1-RELEASE with ktrace and the above does
> not seem to be true.  I get drastically different traces for
> 
>    #! /bin/sh
>    exec /bin/pwd
> 
> and
> 
>    #! /bin/sh
>    /bin/pwd
> 
> Rahul

I know that the FreeBSD Bourne shell doesn't do this, nor does the PDKSH.
I checked and the copy of the AT&T Korn shell I have (for BSDi) does do what
David Korn says.

> 
> > Date:  Fri, 19 Feb 99 11:43:59 EST
> > From:  Mikhail Teterin <mi@misha.cisco.com>
> > To:    current@freebsd.org
> > Message-Id: <199902191644.LAA08791@misha.cisco.com>
> > Subject: sh(1) -- exec vs. fork
> > Reply-To: mi@aldan.algebra.com
> 
> > I just finished going through a couple of crontabs prepending the
> > command-lines with ``exec'', when it hit me.
> > 
> > Can shell itself recognize, there will be no more commands and just
> > proceed to exec without forking? What would this break?
> ...
> 
> 
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 Brian Feldman					  _ __  ___ ___ ___  
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