Simple script to get unused database parameter groups

db_parameter_queries.sh

#!/bin/bash

# NOTE you'll want to prefix this with any account assumption/shell prefix/saml/etc or redirect as needed :) 
# TODO Cluster groups?

# Get all parameter groups
all_groups=$(aws rds describe-db-parameter-groups --query 'DBParameterGroups[].DBParameterGroupName' --output text)

# Get parameter groups used by DB instances
used_groups=$(aws rds describe-db-instances --query 'DBInstances[].DBParameterGroups[].DBParameterGroupName' --output text)

# Compare the lists to find unused groups
for group in $all_groups; do
  if [[ $used_groups != *$group* ]]; then
    echo "Unused parameter group: $group"
  fi
done