alt Hacker NewsEPUB got specific structure/components, which includes metadata files, and isn't just `zip book.epub book.html book.css *.jpg`. Of course can set-up from start to have expected structure, write xhtml files as expected, write metadata files manually, and create epub with just `zip book.epub -r *` but is more convenient via script/app.
I think you can make the metadata files with roughly a five-line Perl script.