A shell script that uses pdftk to break a PDF file into smaller files, each with an equal number of pages

extract_pages.sh

#!/bin/zsh

if (($# != 2)); then
    echo
    echo "This script breaks the given PDF file into a set of PDf files,"
    echo "each with block_size pages."
    echo
    echo "Usage:"
    echo "  extract_pages.sh filename block_size"
    echo
    exit 1
fi

filename=$1
block_size=$2

page_count=$(pdftk $filename dump_data &>/dev/null | grep NumberOfPages | awk '{print $2}')
echo; echo "Detected $page_count pages in the PDF file"; echo

num_blocks=$(($page_count / $block_size))

for i ({1..$num_blocks}); do
    start_page=$((($i - 1) * $block_size + 1))
    end_page=$(($i * $block_size))
    echo "Running command:"
    echo "  pdftk $filename cat ${start_page}-${end_page} output ${i}.pdf"
    pdftk $filename cat ${start_page}-${end_page} output ${i}.pdf
    echo
done