describe_subnets.sh

#!/bin/bash
#
# AWS - Describe subnets
#
export AWS_DEFAULT_REGION=us-east-1
echo "AWS_DEFAULT_REGION= " $AWS_DEFAULT_REGION
#
# Is there a VPC with CIDR 172.16.0.0/16?
default_cidr="172.16.0.0/16"
read -p "CIDR? (default: $default_cidr)  " cidr
#
# if $cidr value that's input has regex pattern ^$, it's empty, so use default
if [[ "$cidr" =~ ^$ ]]; then
    cidr=$default_cidr
    echo "using default CIDR $default_cidr";
fi
# Describe VPCs
# Describe VPC results fields
# 1- "VPCS"
# 2- CidrBlock
# 3- DhcpOptionsId
# 4- InstanceTenancy
# 5- IsDefault
# 6- State
# 7- VpcId
#
# get VpcId from field 7
vpc=$(aws ec2 describe-vpcs --output text --filters Name=cidr,Values=$cidr | cut -f 7)
# if $vpc = regex ^$, then no VPC with specified CIDR
if [[ "$vpc" =~ ^$ ]]; then
    echo "No VPC with CIDR $cidr"
    exit
#lse
#   aws ec2 describe-vpcs --output table   --filters Name=cidr,Values=$cidr
fi
#
# Describe subnets
# Describe subnet fields
# 1- "SUBNETS"
# 2- AvailabilityZone
# 3- AvailableIpAddressCount
# 4- CidrBlock
# 5- DefaultForAz
# 6- MapPublicIpOnLaunch
# 7- State
# 8- SubnetId
# 9- VpcId
echo "VPC " $vpc
if [ "$vpc" ]; then
    echo ""
    aws ec2 describe-subnets --output text  --filters Name=vpc-id,Values=$vpc
else
    echo ""
    echo "No VPC subnets for CIDR $cidr"
fi