Bash script to calculate a set of subnets off a network address

ipcalcandplan.sh

#!/usr/bin/env bash

# ip_to_decmial takes a dotted-quad IPv4 address and returns the decimal form
# on stdout.
ip_to_decmial() {
  local ip_bytes=(${1//./ })
  local ip_decimal=0

  for n in 0 1 2 3; do
    ip_decimal=$(( ip_decimal | ip_bytes[n] << 8 * 3 - 8 * n ))
  done

  echo $ip_decimal
}

# decimal_to_ip takes a decimal IPv4 address and returns the dotted-quad form
# on stdout.
decimal_to_ip() {
  local ip_decimal=$1
  local ip_bytes=()

  for n in 0 1 2 3; do
    ip_bytes+=($(( (ip_decimal >> 8 * 3 - 8 * n) & 255 )))
  done
  echo "${ip_bytes[0]}.${ip_bytes[1]}.${ip_bytes[2]}.${ip_bytes[3]}"
}

dec=$(ip_to_decmial "$1")
shift
while (( "$#" )); do
  params=(${1/\*/ })
  shift
  n=1
  while [ "${n}" -le "${params[0]}" ]; do
    echo "$(decimal_to_ip "${dec}")/${params[1]}"
    dec=$((dec + 2 ** (32-params[1])))
    ((n++))
  done
done

Run this script like so:

./ipcalcandplan.sh 10.0.0.0 4*24 8*25

This would calculate the first 4 /24s, and then the next 8 /25s, starting from 10.0.0.0.

Output:

10.0.0.0/24
10.0.1.0/24
10.0.2.0/24
10.0.3.0/24
10.0.4.0/25
10.0.4.128/25
10.0.5.0/25
10.0.5.128/25
10.0.6.0/25
10.0.6.128/25
10.0.7.0/25
10.0.7.128/25