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Top Forums Shell Programming and Scripting How to change ip addressing format from CIDR notation to netmask and vice versa? Post 302927657 by Corona688 on Thursday 4th of December 2014 10:48:12 AM
Old 12-04-2014
What's your shell? What's your system?

CIDR to netmask is straightforward if tedious -- just binary math. Shells aren't generally that good at it but modern BASH has large enough numbers to handle this.

Code:
#!/bin/bash

while IFS="/" read IP S
do
        M=$(( 0xffffffff ^ ((1 << (32-S)) -1) ))
        echo "$IP netmask $(( (M>>24) & 0xff )).$(( (M>>16) & 0xff )).$(( (M>>8) & 0xff )).$(( M & 0xff ))"
done

If you have an older bash, it may generate negative values due to overflowing its 32-bit integers.
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Paranoid::Network::IPv4(3pm)				User Contributed Perl Documentation			      Paranoid::Network::IPv4(3pm)

NAME
Paranoid::Network::IPv4 - IPv4-related functions VERSION
$Id: IPv4.pm,v 0.1 2012/05/29 21:37:44 acorliss Exp $ SYNOPSIS
use Paranoid::Network::IPv4; @net = ipv4NetConvert($netAddr); $rv = ipv4NetIntersect($net1, $net2); or use Paranoid::Network::IPv4 qw(:all); print "Valid IP address " if $netAddr =~ /^@{[ IPV4REGEX ]}$/; @net = ipv4NetConvert($netAddr); $broadcast = $net[IPV4BRDCST]; DESCRIPTION
This module contains a few convenience functions for working with IPv4 addresses. By default only the subroutines themselves are imported. Requesting :all will also import the constants as well. SUBROUTINES
/METHODS ipv4NetConvert @net = ipv4NetConvert($netAddr); This function takes an IPv4 network address in string format and converts it into an array containing the base network address, the broadcast address, and the netmask, in integer format. The network address can have the netmask in either CIDR format or dotted quads. In the case of a single IP address, the array with only have one element, that of the IP in integer format. Passing any argument to this function that is not a string representation of an IP address (including undef values) will cause this function to return an empty array. ipv4NetIntersect $rv = ipv4NetIntersect($net1, $net2); This function tests whether an IP or subnet intersects with another IP or subnet. The return value is essentially boolean, but the true value can vary to indicate which is a subset of the other: -1: destination range encompasses target range 0: both ranges do not intersect at all 1: target range encompasses destination range The function handles the same string formats as ipv4NetConvert, but will allow you to test single IPs in integer format as well. CONSTANTS
These are only imported if explicity requested or with the :all tag. MAXIPV4CIDR Simply put: 32. This is the largest CIDR notation supported in IPv4. IPV4REGEX Regular expression: qr/(?:d{1,3}.){3}d{1,3}/sm You can use this for validating IP addresses as such: $ip =~ m#^@{[ IPV4REGEX ]}$#; or to extract potential IPs from extraneous text: (@ips) = ( $string =~ m#(@{[ IPV4REGEX ]})#gsm); IPV4CIDRRGX Regular expression: qr#(@{[ IPV4REGEX ]})(?:/(d+|@{[ IPV4REGEX ]}))?#sm By default this will extract an IP or CIDR notation network address: ($net, $mask) = ( $ip =~ m#^@{[ IPV4CIDRRGX ]}$# ); In the case of a simple IP address $mask will be undefined. IPV4BASE This is the ordinal index of the base network address as returned by ipv4NetConvert. IPV4BRDCST This is the ordinal index of the broadcast address as returned by ipv4NetConvert. IPV4MASK This is the ordinal index of the network mask as returned by ipv4NetConvert. DEPENDENCIES
o Paranoid o Paranoid::Network::Socket BUGS AND LIMITATIONS
AUTHOR
Arthur Corliss (corliss@digitalmages.com) LICENSE AND COPYRIGHT
This software is licensed under the same terms as Perl, itself. Please see http://dev.perl.org/licenses/ for more information. (c) 2012, Arthur Corliss (corliss@digitalmages.com) perl v5.14.2 2012-05-29 Paranoid::Network::IPv4(3pm)
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