Split PDF to multiple PDFs by a user-specifid page range

my_pdf_splitter.sh

#!/bin/bash

###############################################################################
# Split PDF to the preferred PDFs by the specified pages                      #
###############################################################################

# Benedek Danko

# Variables:
input_file="$1"
increment="$2"
max_page_num=$(pdftk "$1" dump_data | grep NumberOfPages | awk '{print $2}')
echo "Total number of pages:" $max_page_num
max_page_num=$(expr $max_page_num - $increment)


echo "Number of pages per output file(s):" $increment

for i in $(seq 1 $increment $max_page_num);
do
    num_first=$i
    num_second="$(expr $i + $increment - 1)"
    idx=$(expr $num_second / $increment)
    pdftk "$input_file" cat "$num_first"-"$num_second" output out$idx.pdf
done

echo "Done."

Example run:

./pdf_splitter.sh input.pdf 5