List S3 bucket sizes and object counts via CloudWatch

s3-sizes.sh

#!/bin/bash -eu
set -o pipefail

START=$(date -u -d "3 days ago" +%FT%TZ)
END=$(date -u +%FT%TZ)

get_metric() {
  local bucket="${1}"
  local region="${2}"
  local metric="${3}"
  local storage="${4}"

  aws cloudwatch get-metric-statistics \
    --namespace AWS/S3 \
    --metric-name "${metric}" \
    --dimensions Name=BucketName,Value="${bucket}" Name=StorageType,Value="${storage}" \
    --statistics Average \
    --start-time "${START}" \
    --end-time "${END}" \
    --period 86400 \
    --region "${region}" \
    --query 'sort_by(Datapoints, &Timestamp)[-1].Average' \
    --output text 2> /dev/null || echo "None"
}

printf "%-63s %-12s %20s %15s\n" "BUCKET" "REGION" "SIZE" "OBJECTS"

while read -r bucket; do
  [ -z "${bucket}" ] && continue

  region=$(aws s3api get-bucket-location \
    --bucket "${bucket}" \
    --query LocationConstraint \
    --output text)

  [[ "${region}" == "None" || "${region}" == "null" ]] && region="us-east-1"

  size=$(get_metric "${bucket}" "${region}" BucketSizeBytes StandardStorage)
  count=$(get_metric "${bucket}" "${region}" NumberOfObjects AllStorageTypes)

  [[ "${size}" != "None" ]] && size=$(printf "%.0f" "${size}")
  [[ "${count}" != "None" ]] && count=$(printf "%.0f" "${count}")

  if [[ "${size}" != "None" ]]; then
    hr=$(numfmt --to=iec --suffix=B "${size}" 2> /dev/null || echo "${size}")
  else
    hr="N/A"
  fi

  printf "%-63s %-12s %20s %15s\n" \
    "${bucket}" "${region}" "${hr}" "${count:-0}"

done