Shell Programming and Scripting

#!/bin/bash

# Convert IP to int
function ip_to_int() {
    SaveIFS=$IFS
    IFS=.
    typeset -a IParr=($1)
    IFS=$SaveIFS

    result=0
    for ((i=0;i<4;i+=1)); do
        result=$(($result * 256))
        result=$((${IParr[$i]} + $result))
    done

    echo $result
}

# Convert IP from int
function int_to_ip() {
    result=$1
    byte=""
    for ((i=0;i<3;i+=1)); do
        byte=.$(($result % 256))$byte
        result=$(($result / 256))
    done
    echo $result$byte
}

# Calculate number of addresses in subnet 
function cidr_to_netsize() {
    echo $((1 << 32 - $1))
}

# Calculate bitmask for the 'host' part
function cidr_to_hostmask() {
    echo $(($(($((1 << $1)) - 1)) << $((32 - $1))))
}

# Get the Network destination from the IP & Subnet mask
function get_network_address() {
    SaveIFS=$IFS
    IFS=.
    typeset -a IParr=($1)
    typeset -a NMarr=($2)
    IFS=$SaveIFS

    echo $((${IParr[0]} & ${NMarr[0]})).$((${IParr[1]} & ${NMarr[1]})).$((${IParr[2]} & ${NMarr[2]})).$((${IParr[3]} & ${NMarr[3]}))
}

# Get the broadcast address from the IP & Subnet mask
function get_broadcast_address() {
    SaveIFS=$IFS
    IFS=.
    typeset -a IParr=($1)
    typeset -a NMarr=($2)
    IFS=$SaveIFS

    echo $((${IParr[0]} | (255 ^ ${NMarr[0]}))).$((${IParr[1]} | (255 ^ ${NMarr[1]}))).$((${IParr[2]} | (255 ^ ${NMarr[2]}))).$((${IParr[3]} | (255 ^ ${NMarr[3]})))
}

[[ $# != 2 ]] && {
   echo "Usage: $0 CIDR IP-Address"
   exit 1
}

# Given values
cidr=$1
ip=$2

# Calculations
netsize=$(cidr_to_netsize $cidr)
hostmask=$(cidr_to_hostmask $cidr)
subnet=$(int_to_ip $hostmask)
int_ip=$(ip_to_int $2)
ip_from_int=$(int_to_ip $int_ip)
netaddr=$(get_network_address $ip $subnet)
broadcast=$(get_broadcast_address $ip $subnet)

# Output
echo "Given CIDR: $cidr"
echo "    CIDR to NETWORK SIZE: $netsize"
echo "    CIDR to HOST MASK: $hostmask"
echo "    HOST MASK to SUBNET MASK: $subnet"
echo 
echo "Given IP: $ip"
echo "    IP to INT: $int_ip"
echo "    INT to IP: $ip_from_int"
echo
echo "Given IP & SUBNET MASK: $ip & $subnet"
echo "    IP & SUBNET MASK to NETWORK ADDRESS: $netaddr"
echo "    IP & SUBNET MASK to BROADCAST ADDRESS: $broadcast"
exit 0

$ ./ip2int 16 192.168.10.15
Given CIDR: 16
        CIDR to NETWORK SIZE: 65536
        CIDR to HOST MASK: 4294901760
        HOST MASK to SUBNET MASK: 255.255.0.0

Given IP: 192.168.10.15
        IP to INT: 3232238095
        INT to IP: 192.168.10.15

Given IP & SUBNET MASK: 192.168.10.15 & 255.255.0.0
        IP & SUBNET MASK to NETWORK ADDRESS: 192.168.0.0
        IP & SUBNET MASK to BROADCAST ADDRESS: 192.168.255.255