Finally a conformable way to navigate my library.
Type bookshelf followed by a grep expression inside the directory
with to book you are looking for. Then type the index of the correct
book and it will be opened.
This is very useful if you want do not know the exact name of the book or looking for an author, or if the filename starts with the author, but you do not know who that is; and you have a lot of books in some categories.
By default xpdf used for opening the document, if $TERM=linux, then jfbview is used. If you want another viewer, export that command to PDFVIEWER.