[chef] knife data bag from file with --all

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I am trying to get the --all option to work:

knife data bag from file [bag_name] --all # all data bag items assuming that
data bags are in the ./data_bags/

Although I successfully used create to first define a data bag on the server
and I can use from file with a data bag and an item .json file to upload a
single item, I cannot figure out how to use the --all option to upload all
items for a specified data bag.  When I run it, a blank line is returned and
nothing is uploaded.

Does anyone have a working example of the --all option?

On a related topic, what is the difference inusing knife upload to upload data
bags or other content as compared to using the knife from file options?