Quick and dirty bash script to create a pdf with mobius double sided printing

mobius.sh

#!/bin/bash

# https://byorgey.wordpress.com/how-to-print-things/#m%C3%B6bius-double-sided
# https://mathlesstraveled.com/2016/01/08/a-new-way-to-read-and-print-double-sided-paper/
# https://shreevatsa.net/mobius-print/

if [ $# -eq 0 ]; then
    echo $#
    echo "usage: $0 pdf_file"
    exit
fi

total=$(pdftk $1 dump_data | grep NumberOfPages | cut -d ':' -f 2)

half=$(echo "$total"/2 + "$total"%2 | bc)
half_p_1=$(echo $half + 1 | bc)

forward_pages=($(seq 1 1 $half))
reverse_pages=($(seq $half_p_1 1 $total))

pages=""
for i in "${!forward_pages[@]}"; do
    pages+="${forward_pages[i]} "
    pages+="${reverse_pages[i]} "
done

output_filename=$(basename $1 .pdf)

# now generate the pdf
pdftk $1 cat $pages output "$output_filename"_mobius.pdf