Pure shell IPv4 subnet calculations

addr.sh

#!/bin/sh

exit_error()
{
	echo "$1" >&2 && exit 1
}


valid_ip()
{
	local ip=$1
	local stat=0

	echo $ip | grep -qE '^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$' || stat=1

	if [ $stat -eq 0 ]; then
		OIFS=$IFS
		IFS='.'
		set -- $ip
		IFS=$OIFS
		[ $1 -le 255 ] && [ $2 -le 255 ] \
		    && [ $3 -le 255 ] && [ $4 -le 255 ] || stat=1
	fi
	return $stat
}



netmask2cidr ()
{
    # Assumes there's no "255." after a non-255 byte in the mask
    local x=${1##*255.}
    set -- 0^^^128^192^224^240^248^252^254^ $(( (${#1} - ${#x})*2 )) ${x%%.*}
    x=${1%%$3*}
    echo $(( $2 + (${#x}/4) ))
}


cidr2netmask ()
{
   # Number of args to shift, 255..255, first non-255 byte, zeroes
   set -- $(( 5 - ($1 / 8) )) 255 255 255 255 $(( (255 << (8 - ($1 % 8))) & 255 )) 0 0 0
   [ $1 -gt 1 ] && shift $1 || shift
   echo ${1-0}.${2-0}.${3-0}.${4-0}
}



_addr_helper ()
{
	local ip cidr mask gateway
	ip=${1%%/*}
	cidr=${1##*/}

	# Convert it to mask format
	mask=`cidr2netmask $cidr 2>/dev/null` || true
	mask=${mask:-$cidr}
	OLDIFS=$IFS
	IFS=.

	set -- $mask $ip
	local netid bcast gateway

	netid=$(( $1 & $5 )).$(( $2 & $6 )).$(( $3 & $7 )).$(( $4 & $8 ))

	set -- $mask $netid
	bcast=$(( $5 + 255 - $1 )).$(( $6 + 255 - $2 )).$(( $7 + 255 - $3 )).$(( $8 + 255 - $4 ))


	set -- $mask $netid $bcast
	
	IFS=$OLDIFS

	local min_host=$(( $8 + 1 ))
	if [ $min_host -lt ${12} ]; then
		gateway=$5.$6.$7.$min_host
	fi
		

	echo "$netid"
	echo "$bcast"
	echo "$gateway"
}


guess_default_gateway()
{
	set -- `_addr_helper $@`
	echo $3
}


broadcast_addr()
{
	set -- `_addr_helper $@`
	echo $2
}



network_addr()
{
	set -- `_addr_helper $@`
	echo $1
}



case $1 in
	valid_ip)
		valid_ip $2
		;;
	gateway)
		guess_default_gateway $2
		;;
	broadcast)
		broadcast_addr $2
		;;
	netmask)
		cidr2netmask $2
		;;
	network)
		network_addr $2
		;;
	cidr)
		netmask2cidr $2
		;;
	*)
		echo "Invalid command!" >&2 && exit 1
		;;
esac