From owner-freebsd-questions@FreeBSD.ORG  Fri Dec 18 10:11:51 2009
Return-Path: <owner-freebsd-questions@FreeBSD.ORG>
Delivered-To: freebsd-questions@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 9F27110656A5;
	Fri, 18 Dec 2009 10:11:51 +0000 (UTC)
	(envelope-from perryh@pluto.rain.com)
Received: from agora.rdrop.com (unknown [IPv6:2607:f678:1010::34])
	by mx1.freebsd.org (Postfix) with ESMTP id 717678FC13;
	Fri, 18 Dec 2009 10:11:51 +0000 (UTC)
Received: from agora.rdrop.com (66@localhost [127.0.0.1])
	by agora.rdrop.com (8.13.1/8.12.7) with ESMTP id nBIABg09039269
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT);
	Fri, 18 Dec 2009 02:11:42 -0800 (PST)
	(envelope-from perryh@pluto.rain.com)
Received: (from uucp@localhost)
	by agora.rdrop.com (8.13.1/8.12.9/Submit) with UUCP id nBIABfGK039268; 
	Fri, 18 Dec 2009 02:11:41 -0800 (PST)
Received: from fbsd61 by pluto.rain.com (4.1/SMI-4.1-pluto-M2060407)
	id AA24581; Fri, 18 Dec 09 02:00:24 PST
Date: Fri, 18 Dec 2009 01:59:36 -0800
From: perryh@pluto.rain.com
To: wblock@wonkity.com, glarkin@freebsd.org
Message-Id: <4b2b5288.qFxIl6ScdS9yKkZj%perryh@pluto.rain.com>
References: <20091218005102.GA51064@mech-cluster241.men.bris.ac.uk>
	<alpine.BSF.2.00.0912171820130.53881@wonkity.com>
	<4B2ADE9E.6080707@FreeBSD.org>
In-Reply-To: <4B2ADE9E.6080707@FreeBSD.org>
User-Agent: nail 11.25 7/29/05
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Cc: mexas@bristol.ac.uk, freebsd-questions@freebsd.org
Subject: Re: editing a binary file
X-BeenThere: freebsd-questions@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: User questions <freebsd-questions.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-questions>, 
	<mailto:freebsd-questions-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-questions>
List-Post: <mailto:freebsd-questions@freebsd.org>
List-Help: <mailto:freebsd-questions-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-questions>, 
	<mailto:freebsd-questions-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 18 Dec 2009 10:11:51 -0000

Greg Larkin <glarkin@freebsd.org> wrote:
> ...
> > truncate -4 myfile should get rid of the last four bytes.  Maybe
> > there's a similar efficient way to truncate the start of a file.
>
> This should do it:
>
> dd if=oldfile of=newfile bs=1 skip=4

Or, perhaps marginally more efficient:

dd if=oldfile of=newfile bs=4 skip=1