# Look up the versions of a bag in the storage service

This guide explains how to look up a bag which has been stored in the storage service.

You need to know:

* The space and external identifier of the bag
* The API URL for your storage service instance
* The token URL for your storage service instance
* A client ID and secret for the storage service
* An upload bucket for the storage service

To look up a bag in the storage service:

1. Fetch an access token for the OAuth2 credentials grant:

   ```
   curl -X POST "$TOKEN_URL" \
     --data grant_type=client_credentials \
     --data client_id="$CLIENT_ID" \
     --data client_secret="$CLIENT_SECRET"
   ```

   This will return a response like:

   ```
   {"access_token":"eyJraWQi...","expires_in":3600,"token_type":"Bearer"}
   ```

   Remember the `access_token`.
2. Make a GET request to the /bags API, passing the space and external identiifer in the path:

   ```
   curl "$API_URL/bags/$SPACE/$EXTERNAL_IDENTIFIER/versions" \
     --header "Authorization: $ACCESS_TOKEN"
   ```

   This will return a list of versions, or a 404 error if there are no versions.