ebook-formats

#!/bin/sh
#
# NAME
#
#   ebook-formats - convert ebooks to useful formats
#
# SYNOPSIS
#
#   ebook-formats [-d] <dir>
#
# DESCRIPTION
#
#   This script recursively searches for all EPUB and MOBI files in the
#   given directory and converts EPUB to MOBI if the MOBI version of an
#   EPUB file does not exist (and vice versa).  It also converts the
#   EPUB version to a plain-text file for easy grepping.
#
# OPTIONS
#
#     -d, --dry     dry run (i.e., print commands)
#
# BUGS
#
#   Since the conversion commands are piped to sh(1), it will fail if
#   the filenames contain certain characters, e.g., a single quote.
#   Fixing it will introduce unnecessary complexity and it is better and
#   easier to detox the filenames by first running goop(1).
#
# DEPENDENCIES
#
#   ebook-convert(1) and parallel(1)
#

parallel="/usr/bin/parallel --eta --keep-order"
case "$1" in
    --dry|-d)
        parallel="/bin/cat"
        shift ;;
    *)
        [ -d "$1" ] || {
            echo >&2 "${0##*/}: '$1' is an invalid directory"
            echo >&2 "usage: ${0##*/} [-d] <dir>"
            exit 1
        }
esac

echo >&2 "${0##*/}: converting epub <-> mobi"
{
    find "$1" -type f -name '*.epub' |
        while IFS= read -r epub
        do
            mobi="${epub%.*}.mobi"
            [ -f "$mobi" ] || echo ebook-convert "'$epub'" "'$mobi'"
        done

    find "$1" -type f -name '*.mobi' |
        while IFS= read -r mobi
        do
            epub="${mobi%.*}.epub"
            [ -f "$epub" ] || echo ebook-convert "'$mobi'" "'$epub'"
        done
} | $parallel

# I do this after EPUB <-> MOBI to ensure that an EPUB version exists.
echo >&2 "${0##*/}: converting epub -> text"
{
    find "$1" -type f -name '*.epub' |
        while IFS= read -r epub; do
            txt="${epub%.*}.txt"
            [ -f "$txt" ] || echo ebook-convert "'$epub'" "'$txt'"
        done
} | $parallel