You can save them to a csv with the calibredb list_categories command, see ==>>
Command Line Interface
But there's no easy way to add them into library because of calibre's "a category will only be retained if its attached to a book' rule.
Because it only uses standard features of calibre and your email accounts (or similar) I'd call my method a process, rather than a
patch.
- Add an empty book with a 'blank' epub to the library.
- Apply all the tags to that book with the Tags Editor
- Polish the Book with the update metadata option checked
- Save the Book (ePub only) to Desktop
- Email the ePub to your friend,
- Friend saves the ePub attachment to his/her desktop
- Friend drag-drops the ePub from their desktop into their library
See screen shots and attached epub
I'd call having to retain placeholder books with category lists a
kludge. I've been wishing for a controlled vocabulary option on categories since I started using calibre in 2011. But I assume its not easy to do, otherwise someone would have done it.
BR