A simple IPv4 calculator. Takes an IP and netmask and calculates some details about the network in ksh.

ips_in_range

#!/bin/ksh
set -o errexit -o pipefail -o nounset -o noclobber -o noglob
set +o monitor
export PATH=/usr/bin:/bin:/usr/sbin:/sbin

# Convert the IP to an integer so do calculations on it
dottedQuad2int() {
	local IFS=.
	local ip
	set -A ip $* 0 0 0 0
	echo $(( (${ip[0]}<<24) + (${ip[1]}<<16) + (${ip[2]}<<8) + ${ip[3]} ))
}

int2dottedQuad() {
	local int=$1

	local ip=""
	for b in 24 16 8 0; do
		ip="$ip.$(( int >> b & 0xff ))"
	done
	echo ${ip#.}
}

netmask2cidr() {
	local c m n=$( dottedQuad2int "$1" )
	typeset -i2 n
	typeset -i10 c=0

	m=${n#2#}
	while [[ $m = 1* ]]; do
		c=$((++c))
		m=${m#1}
	done

	if (( m != 0 )); then
		echo "Invalid netmask!" >&2
		exit 1
	fi

	echo "$c"
}

ip=$1
cidr=${2:-}

[ -z "$cidr" ] && [[ $ip = */* ]] && cidr=${ip#*/}
[[ $cidr = *.* ]] && cidr=$( netmask2cidr "$cidr" )

if (( cidr > 32 )); then
    echo "Invalid netmask!" >&2
    exit 1
fi

ip=${ip%/*}
ip=$(dottedQuad2int "$ip" )

integer ip
integer cidr

integer netmask=$(( 0xFFFFFFFF << (32 - cidr) ))
integer network="$((   ip &  netmask & 0xFFFFFFFF ))"
integer broadcast="$(( ip | ~netmask & 0xFFFFFFFF ))"

echo "IP: $( int2dottedQuad "$ip" )/$cidr"
echo "Netmask: $( int2dottedQuad "$netmask" )"
echo "Network: $( int2dottedQuad "$network" )"
echo "Broadcast: $( int2dottedQuad "$broadcast" )"

(( cidr > 30 )) && exit

integer i=$((   network & ~netmask ))
integer e=$(( broadcast & ~netmask ))

echo "IPs: ($(( e - i - 1 )))"
# start with the first IP after the network address
# end one before the broadcast address
while (( i < e -1 )); do
	i=$((i + 1))
	echo -n " "
	int2dottedQuad $(( network + i ))
done