From owner-freebsd-questions@FreeBSD.ORG  Fri Jul 15 03:23:20 2005
Return-Path: <owner-freebsd-questions@FreeBSD.ORG>
X-Original-To: freebsd-questions@freebsd.org
Delivered-To: freebsd-questions@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id E680C16A41C
	for <freebsd-questions@freebsd.org>;
	Fri, 15 Jul 2005 03:23:20 +0000 (GMT)
	(envelope-from dan@dan.emsphone.com)
Received: from dan.emsphone.com (dan.emsphone.com [199.67.51.101])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 98AB743D46
	for <freebsd-questions@freebsd.org>;
	Fri, 15 Jul 2005 03:23:20 +0000 (GMT)
	(envelope-from dan@dan.emsphone.com)
Received: (from dan@localhost)
	by dan.emsphone.com (8.13.1/8.13.3) id j6F3NK6v017826;
	Thu, 14 Jul 2005 22:23:20 -0500 (CDT) (envelope-from dan)
Date: Thu, 14 Jul 2005 22:23:20 -0500
From: Dan Nelson <dnelson@allantgroup.com>
To: hzs202@nyu.edu
Message-ID: <20050715032319.GA98600@dan.emsphone.com>
References: <42D7236A.6010803@gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <42D7236A.6010803@gmail.com>
X-OS: FreeBSD 5.4-STABLE
X-message-flag: Outlook Error
User-Agent: Mutt/1.5.9i
Cc: freebsd-questions@freebsd.org
Subject: Re: Problem Piping iostat -c to awk!
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, 15 Jul 2005 03:23:21 -0000

In the last episode (Jul 14), Hakim Singhji said:
> I am having problems with a shell script that I am writing. I am
> looking to pipe the output of iostat to awk however the shell is
> hanging... even at the command line it hangs. The code looks like
> this:
> 
> 	# iostat -c 300 2 | egrep -v '[a-zA-Z]|^$' | awk '{print $1}'
> 
> This code hangs for me... now when I just pipe iostat through the
> egreped patter it is fine. It's when it is passed to awk that I have
> problems... now of course if I simplify the output to:
> 
> 	# iostat | egrep -v '[a-zA-Z]|^$' | awk '{print $1}'
> 
> it works just fine... so it has to be the awk. What is the problem?

Actually grep is the culprit.  It buffers its output when piped to
another program for efficiency.  Try adding --line-buffering, or just
let awk handle your regular expression:

iostat -c 300 1 | awk '!/[a-zA-Z]|^$/ {print $1}'


-- 
	Dan Nelson
	dnelson@allantgroup.com