Group S3 keys with a delimiter

Part 39 of AWS from Zero. This lesson keeps the scope to one S3 behavior you can verify from the terminal.

What we are learning

A delimiter groups keys between the prefix and the next delimiter occurrence. With /, S3 can return folder-like CommonPrefixes.

Before you run it

aws sts get-caller-identity
REGION="ap-south-1"
BUCKET="replace-with-your-private-demo-bucket"

Use a private general purpose bucket that you own. Replace every placeholder before running a write or delete command.

The command

aws s3api list-objects-v2 \
  --bucket "$BUCKET" \
  --prefix "reports/" \
  --delimiter "/"

A successful configuration command may return no output. Treat inspection as a separate required step.

Inspect the result

aws s3api list-objects-v2 \
  --bucket "$BUCKET" \
  --prefix "reports/" \
  --delimiter "/" \
  --query "{Files:Contents[].Key,Groups:CommonPrefixes[].Prefix}"

Read the returned fields rather than assuming the write succeeded exactly as intended.

One tiny variation

aws s3api list-objects-v2 \
  --bucket "$BUCKET" \
  --prefix "reports/2026/" \
  --delimiter "/" \
  --query "CommonPrefixes[].Prefix" \
  --output text

Move the prefix one level deeper to explore the next group.

Common mistake

CommonPrefixes are calculated from key names; they are not directory resources you can permission or delete independently.

Cleanup

# This lesson does not require an additional persistent resource.
aws s3api head-bucket --bucket "$BUCKET"

Keep the shared demo bucket for the next lesson, or remove only the configuration and objects created here.

Next, we will learn Control S3 listing pagination.

Official AWS CLI reference