A script that takes a .djvu file and generates another .djvu using the given page range. You can run this many times with https://gist.github.com/LouisRitchie/a797882ce9b934b2f08a649bf7261776 to a bunch of chapters out of a djvu.

get_chapter_from_djvu.sh

# USAGE: ./script.sh [input file] [start page] [end page] [output file]
# Using this script asynchronously would be extremely painful
# > you're a big guy
# for you

input_file=$1
output_file=$4
start_page=$2
end_page=$3

range=$(seq $start_page $end_page)
temp_files=$(echo $range | tr '\n' ' ' | sed -e "s/ /\.djvu /g") # 1.djvu 2.djvu 3.djvu

for i in $range
do
  djvused $input_file -e "select $i; save-page-with $i.djvu"
done

djvm -c $output_file $temp_files
rm $temp_files