From owner-freebsd-questions  Thu Jun  6 22:43:32 2002
Delivered-To: freebsd-questions@freebsd.org
Received: from wonkity.com (wonkity.com [63.93.4.4])
	by hub.freebsd.org (Postfix) with ESMTP id 5659037B404
	for <freebsd-questions@FreeBSD.ORG>; Thu,  6 Jun 2002 22:43:27 -0700 (PDT)
Received: from wonkity.com (localhost.wonkity.com [127.0.0.1])
	by wonkity.com (8.12.1/8.11.6) with ESMTP id g575hQuF076856;
	Thu, 6 Jun 2002 23:43:26 -0600 (MDT)
	(envelope-from wblock@wonkity.com)
Received: from localhost (wblock@localhost)
	by wonkity.com (8.12.1/8.12.1/Submit) with ESMTP id g575hQuC076853;
	Thu, 6 Jun 2002 23:43:26 -0600 (MDT)?g
	(envelope-from wblock@wonkity.com)
Date: Thu, 6 Jun 2002 23:43:26 -0600 (MDT)
From: Warren Block <wblock@wonkity.com>
To: BSD Freak <bsd-freak@mbox.com.au>
Cc: FreeBSD Questions <freebsd-questions@FreeBSD.ORG>
Subject: Re: Converting decimal dotted subnet mask to CIDR in a script
In-Reply-To: <f9079af91739.f91739f9079a@mbox.com.au>
Message-ID: <Pine.BSF.4.21.0206062337160.76838-100000@wonkity.com>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: owner-freebsd-questions@FreeBSD.ORG
Precedence: bulk
List-ID: <freebsd-questions.FreeBSD.ORG>
List-Archive: <http://docs.freebsd.org/mail/> (Web Archive)
List-Help: <mailto:majordomo@FreeBSD.ORG?subject=help> (List Instructions)
List-Subscribe: <mailto:majordomo@FreeBSD.ORG?subject=subscribe%20freebsd-questions>
List-Unsubscribe: <mailto:majordomo@FreeBSD.ORG?subject=unsubscribe%20freebsd-questions>
X-Loop: FreeBSD.ORG

On Fri, 7 Jun 2002, BSD Freak wrote:

> I have a variable in a script we use
> 
> $MASK=255.255.255.0
> 
> Is there a utility or an easy way to process $MASK and get 
> 
> $MASKCIDR=24
> 
> the CIDR value of 255.255.255.0

Okay:

#!/usr/bin/perl -w
($byte1, $byte2, $byte3, $byte4) = split(/\./, $ARGV[0].".0.0.0.0");
$num = ($byte1 * 16777216) + ($byte2 * 65536) + ($byte3 * 256) + $byte4;
$bin = unpack("B*", pack("N", $num));
$count = ($bin =~ tr/1/1/);
print "$bin = $count bits\n";

The first line is fluff to allow command-line operation.  The second
line converts dotted quad to plain decimal.  The third line converts
decimal to a binary string.  Line four counts the set bits.

However, no test is made on the validity of the mask--the bits should be
contiguous from the left.  I'm pretty sure there's an easy regular
expression which would do that, but it's getting late.

-Warren Block * Rapid City, South Dakota USA




To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-questions" in the body of the message