From owner-freebsd-standards@FreeBSD.ORG  Fri Jul  7 19:24:02 2006
Return-Path: <owner-freebsd-standards@FreeBSD.ORG>
X-Original-To: freebsd-standards@freebsd.org
Delivered-To: freebsd-standards@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 1909C16A4DA
	for <freebsd-standards@freebsd.org>;
	Fri,  7 Jul 2006 19:24:02 +0000 (UTC)
	(envelope-from jan.grant@bristol.ac.uk)
Received: from dirg.bris.ac.uk (dirg.bris.ac.uk [137.222.10.102])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 9166E43D73
	for <freebsd-standards@freebsd.org>;
	Fri,  7 Jul 2006 19:24:01 +0000 (GMT)
	(envelope-from jan.grant@bristol.ac.uk)
Received: from mail.ilrt.bris.ac.uk ([137.222.16.62])
	by dirg.bris.ac.uk with esmtp (Exim 4.60)
	(envelope-from <jan.grant@bristol.ac.uk>) id 1Fyvvi-0004G3-2Y
	for freebsd-standards@freebsd.org; Fri, 07 Jul 2006 20:24:00 +0100
Received: from cse-jg.cse.bris.ac.uk ([137.222.12.37]:50767)
	by mail.ilrt.bris.ac.uk with esmtps (TLSv1:AES256-SHA:256)
	(Exim 4.50) id 1Fyvvb-0002NT-Cm; Fri, 07 Jul 2006 20:23:57 +0100
Date: Fri, 7 Jul 2006 20:23:50 +0100 (BST)
From: Jan Grant <jan.grant@bristol.ac.uk>
X-X-Sender: cmjg@tribble.ilrt.bris.ac.uk
To: freebsd-standards@freebsd.org
Message-ID: <20060707201402.T14116@tribble.ilrt.bris.ac.uk>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
X-Spamassassin: mail.ilrt.bris.ac.uk
X-Spam-Score: 0.0
X-Spam-Level: /
X-Spam-Score: -1.4
X-Spam-Level: -
Subject: stdio/sh behaviour guaranteed?
X-BeenThere: freebsd-standards@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Standards compliance <freebsd-standards.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-standards>, 
	<mailto:freebsd-standards-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-standards>
List-Post: <mailto:freebsd-standards@freebsd.org>
List-Help: <mailto:freebsd-standards-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-standards>, 
	<mailto:freebsd-standards-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 07 Jul 2006 19:24:02 -0000

Consider the following snippet.

[[[
#!/bin/sh

echo one > t
while read line
do
        echo $line
        case $line in
        one) echo two >> t
                ;;
        two) echo three >> t
                ;;
        esac
done <t
]]]

This produces three lines of output on FreeBSD: which is what I'd 
intuitively expect and it's certainly useful behaviour.

I'm just trying to determine if that behaviour is one that I can rely on 
- in other words, I guess, if stdio performs a "short read" that fails 
to fill a buffer, and the underlying file is then extended outside the 
process, will another attempt to read from the FILE* (or a test of feof, 
say) honour the new, longer file contents? And in particular, is the 
idiom above blessed by appropriate posix standards?

I'm having a hard time pinning down any appropriate standards that deal 
with this.

Cheers,
jan

PS. Would appreciate a CC: on any responses.

-- 
jan grant, ISYS, University of Bristol. http://www.bris.ac.uk/
Tel +44 (0)117 3317661   http://ioctl.org/jan/
Not as randy or clumsom as a blaster.