Discovers available IPs in AWS Subnets. Relies on default aws config

find-free-ips.sh

#!/bin/bash

while [[ $# -gt 1 ]]
do
key="$1"

case $key in
    -s|--subnet)
    SUBNETS="$2"
    shift # past argument
    ;;
esac
shift # past argument or value
done

if [ -z "${SUBNETS}" ]; then
     echo -n "Please provide subnet Ids [Comma Separated] : "
     read ID_VAL < /dev/tty
else
   ID_VAL="$SUBNETS"
fi

IFS=',' read -ra my_subnets <<< "$ID_VAL"

for subn in "${my_subnets[@]}" 
do

   cidr=$(aws ec2 describe-subnets --subnet-ids  ${subn} | jq '.Subnets[].CidrBlock' | cut -d"\"" -f2) 

   echo " " 
   echo "Analyzing Subnet ${subn} with CIDR ${cidr}..."
   echo "-------------------------------------------------------------"
   
   all_ips=$(nmap -v -sn ${cidr} | grep "host down" | cut -d' ' -f5)
   
   used_ips=$(aws ec2 describe-instances --filter Name="subnet-id",Values=\"${subn}\" | jq '.Reservations[].Instances[].PrivateIpAddress' | cut -d"\"" -f2)
   
   echo "Used IPs:  "
   echo "---------"
   printf '%s\n ' "${used_ips[@]}"
   
   echo " "
   
   echo "Available IPs:"
   echo "--------------"
   for del in ${used_ips[@]}
   do
     all_ips=(${all_ips[@]/$del})
   done
 
   printf '%s\n' "${all_ips[@]}"
   
   used_ips=()
   all_ips=()   
done