The Nexus Data Import tool is used to push files on your local disk into a running Nexus server and create data items from the file contents.
The option -data_categories [categoryA [categoryB ...]] was added as a part of ACLs. It is optional. You may use it to specify a list of space-separated categories to assign the item to. The default is empty (no item categories). You can only set categories that the authenticating user has 'own' permissions on, through any of the user's groups. The superuser has no restrictions.