Construct a Project Gutenberg url
gutenberg_url(gutenberg_id, mirror, verbose)A named character vector of urls
A vector of Project Gutenberg IDs, or a data frame
containing a gutenberg_id column, such as from the results of
gutenberg_works().
A mirror URL to retrieve the books from. By default uses the
mirror from gutenberg_get_mirror().
Whether to show messages about the Project Gutenberg mirror that was chosen