The long-standing convention here, particularly for command line usage, is that:

- String literals should be in lowercase (because by convention commands, argument names, etc should always be in all-lowercase, eg. "git cherry-pick" not "git cherryPick" or "git CHERRY-PICK")

- Metavariables (stuff the user should fill in) should be in ALL-CAPS.

- Not as strictly adhered to but still useful, [optional part] and {repeatable part}.

So eg. your example might look like:

    $ bin/rails generate scaffold --user=NAME --email=LOGIN

and an example usage would then be:

    $ bin/rails generate scaffold --user=ekimekim --email=ekimekim@example.com

As far as I'm concerned, for documenting command usage, there is no excuse not to use this scheme.