Recursively add all e-books under a directory to the library

Tool to manipulate the your e-book database.
Part of the Calibre e-book library.
More information: <https://manual.calibre-ebook.com/generated/en/calibredb.html>.
Trick copyright: tl;dr; <https://github.com/tldr-pages/tldr>

calibredb add -r {{path/to/directory}}

click the source code to copy install calibredb on any operating system with command-not-found.com