View source for Pro cidr2mask and mask2cidr scripts

taken from   http://forums.gentoo.org/viewtopic-p-6770850.html

function cidr2netmask() 
{ 
        local maskpat="255 255 255 255" 
        local maskdgt="254 252 248 240 224 192 128" 
        set -- ${maskpat:0:$(( ($1 / 8) * 4 ))}${maskdgt:$(( (7 - ($1 % 8)) * 4 )):3} 
        echo ${1-0}.${2-0}.${3-0}.${4-0} 
} 

function netmask2cidr() 
{ 
        # Phase 1: Count how many 255 prefixes 
        local mask="${1//255./xrandomx}" sfx=${1//255.} 
        mask="${mask%%[[:digit:]]*}" 
        set -- ${#mask} ${sfx//./ } 

        # Phase 2: Convert the first non-255 number, rest is supposed to be zeroes 
        mask="0--.128.192.224.240.248.252.254." 
        mask="${mask//$2*}" 
        echo $(( ${1} + ${#mask}/4 )) 
}



Here's the complete script to test these two functions and examples: 
cidrnetmask.sh:
#!/bin/sh 
# Script: cidrnetmask.sh 
# By Vince C <v_cadet AT yahoo.fr>. 
# Released under the WTFPL :D . 

function is_number() 
{ 
   [ -n "${1}" ] && [ -z "${1//[[:digit:]]}" ] 
} 

function cidr2netmask() 
{ 
        local maskpat="255 255 255 255" 
        local maskdgt="254 252 248 240 224 192 128" 
        set -- ${maskpat:0:$(( ($1 / 8) * 4 ))}${maskdgt:$(( (7 - ($1 % 8)) * 4 )):3} 
        echo ${1-0}.${2-0}.${3-0}.${4-0} 
} 

 function netmask2cidr() 
 { 
        # Phase 1: Count how many 255 prefixes 
        local mask="${1//255./xrandomx}" sfx=${1//255.} 
        mask="${mask%%[[:digit:]]*}" 
        set -- ${#mask} ${sfx//./ } 

        # Phase 2: Convert the first non-255 number, rest is supposed to be zeroes 
        mask="0--.128.192.224.240.248.252.254." 
        mask="${mask//$2*}" 
        echo $(( ${1} + ${#mask}/4 )) 
 } 
 # Parse and validate arguments 
 [ -z "$1" ] && exit 0 
 [ "${1%/*}" == "$1" ] && mask="$2" || mask="${1#*/}" 
 [ -z "$mask" ] && echo "No netmask." && exit 0 
 # Check and convert mask 
 ip=${1%/*} 
 # Convert CIDR to netmask and vice versa 
 echo -n "IP: ${ip}/${mask} --> ${ip}/" 
 is_number $mask && cidr2netmask $mask || netmask2cidr $mask

[[category:bash]]