bash script to lock/unlock resources by using an S3 bucket with file versioning

try-acquire-lock-s3.sh

#!/usr/bin/env bash
set -eu

log () {
  echo >&2 "[lock] $@"
}

putLock () {
  aws s3api put-object --region $REGION --bucket $BUCKET --key $LOCK_KEY --output text --query 'VersionId'
}
removeLock () {
  aws s3api delete-object --region $REGION --bucket $BUCKET --key $LOCK_KEY --version-id $LOCK_VERSION --output text
}
listLockVersions () {
  aws s3api list-object-versions --region $REGION --bucket $BUCKET --prefix $LOCK_KEY \
    --page-size=3 --max-items=3 \
    --query '{deleted:DeleteMarkers[*].{date:LastModified,version:VersionId},versions:Versions[*].{date:LastModified,version:VersionId}}'
}

REGION=${REGION:-us-west-2}
LOCK_URL="${1-}"

if ! echo $LOCK_URL | grep -q '^s3:\/\/[^\/]*\/..*'; then
  log "Usage: $0 "'s3://${some-bucket}/${some-lock-file-name}'
  exit 1
fi

BUCKET=$(echo $LOCK_URL | sed 's/^s3:\/\///' | sed 's/\/.*//')
LOCK_KEY=$(echo $LOCK_URL | sed 's/^s3:\/\/[^\/]*\///')

log "trying to acquire lock ${LOCK_URL} at ${REGION}..."
LOCK_VERSION=$(putLock)

log "verifying lock handle '${LOCK_VERSION}'..."
VERSIONS=$(listLockVersions)
MOST_RECENT_VERSION=$(echo $VERSIONS | jq '.versions[0].version' --raw-output)
DATE_PREVIOUS=$(echo $VERSIONS | jq '.versions[1].date' --raw-output | sed 's/^null/1970-01-01T00:00:00.000Z/')
DATE_DELETED=$(echo $VERSIONS | jq '.deleted[0].date' --raw-output | sed 's/^null/1970-01-01T00:00:00.000Z/')

if [ "$MOST_RECENT_VERSION" != "$LOCK_VERSION" ]; then
  log 'failed. Newer lock found. Cleaning up...'
  removeLock >&2
  exit 1
elif [ "$DATE_PREVIOUS" \> "$DATE_DELETED" ]; then
  log 'failed. Existing lock still valid. Cleaning up...'
  removeLock >&2
  exit 1
else
  log 'acquired. Generating command to unlock it...'
  UNLOCK_CMD="aws s3api delete-object --region $REGION --bucket $BUCKET --key $LOCK_KEY --version-id $LOCK_VERSION --output text"
  log $UNLOCK_CMD
  echo $UNLOCK_CMD
fi