A useless script to calculate the network address with the CIDR /xx notation in pure bash.

from_ifconfig_to_network_addr.sh

#!/bin/bash
#
# A useless script to calculate the network address with the CIDR /xx notation
# in pure bash.
# 
# (c) 2019 - thesp0nge - paolo@armoredcode.com
# 
# I started from this gist I found on Github:
# https://gist.github.com/hmmbug/e386274e299ab4d00a9f. The hostname -i command
# doesn't work for a machine resolvng as localhost, i.e. a virtualbox machine. 
# We must consider also hosts with more than a network card... so the interface
# must be a variable parameter.
#
# Then I used this IPprefix_by_netmask implementation in bash I found on
# StackOverflow:
# https://stackoverflow.com/questions/50413579/bash-convert-netmask-in-cidr-notation

IPprefix_by_netmask () { 
   c=0 x=0$( printf '%o' ${1//./ } )
   while [ $x -gt 0 ]; do
       let c+=$((x%2)) 'x>>=1'
   done
   echo /$c ; }
IPconfig_to_netaddr () {
	line=`ifconfig -a $net_i | grep netmask | tr -s " "`
	ip=`echo $line | cut -f 2 -d " "`
	mask=`echo $line | cut -f 4 -d " "`

	IFS=. read -r io1 io2 io3 io4 <<< $ip
	IFS=. read -r mo1 mo2 mo3 mo4 <<< $mask
	NET_ADDR="$((io1 & mo1)).$(($io2 & mo2)).$((io3 & mo3)).$((io4 & mo4))"

	echo $NET_ADDR`IPprefix_by_netmask $mask` ; }

if [ "$#" -ne 1 ]; then
	echo "usage: $0 network interface"
	exit 2
fi
net_i=$1
found=`ifconfig -a $net_i 2> /dev/null`
if [ $? -eq 1 ]; then
	echo $0: $net_i interface not found
	exit 1
fi
IPconfig_to_netaddr $net_i

LICENSE

Copyright (c) 2019 - Paolo Perego - paolo@armoredcode.com

Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation
files (the "Software"), to deal in the Software without
restriction, including without limitation the rights to use,
copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following
conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.