To determine the free and used disk space of a PostgreSQL RDS instance using the AWS CLI, you can use the describe-db-instances command and filter the output to show the FreeStorageSpace and AllocatedStorage fields:
aws rds describe-db-instances --query 'DBInstances[*].{ID:DBInstanceIdentifier, Free:FreeStorageSpace, Allocated:AllocatedStorage}' --output table
This will give you a table with the ID of the RDS instance, the Free disk space in GB, and the Allocated disk space in GB. You can use these values to calculate the used disk space by subtracting the free disk space from the allocated disk space.
