List notification configurations for a bucket.
gcs_list_pubsub(bucket = gcs_get_global_bucket())The bucket for notifications
Cloud Pub/Sub notifications allow you to track changes to your Cloud Storage objects.
As a minimum you wil need: the Cloud Pub/Sub API activated for the project;
sufficient permissions on the bucket you wish to monitor;
sufficient permissions on the project to receive notifications;
an existing pub/sub topic; have given your service account at least pubsub.publisher permission.
https://cloud.google.com/storage/docs/reporting-changes
Other pubsub functions:
gcs_create_pubsub(),
gcs_delete_pubsub(),
gcs_get_service_email()