ACCOUNT_ID=(委任先のAWSアカウントID 12桁)

#カンマ区切りで定義して
REGION=ap-northeast-1,us-east-1,ap-northeast-3

#カンマを改行に置き換えて[while read]以降はそのまま
echo ${REGION} | tr ',' '\n' \
| while read region; do
  echo "##### list organization admin account in ${region}"
  aws --region ${region} guardduty list-organization-admin-accounts
done