epubcat book.epub 1 3
# outputs plain text of pages 1 through 3
I don’t know if epubs have the concept of “pages.” If not, perhaps we can say each 400 chars are a page? A general solution that works for other ebook formats is better (mobi, azw3, etc).
My own thoughts are currently on first converting the book to text via ebook-convert or pandoc and then extracting the needed amount, but this seems awfully inefficient as I intend to only get a little of the beginning of the content.
You can download an example file that can be used for testing here.