[Bash] Convert document pdf with A4 format as a booklet with A5 format

pdf-to-booklet.bash

#!/usr/bin/env bash
#
# pdf-to-booklet.bash
#
# Convert document pdf with A4 format as a booklet with A5 format.
# A output/ folder will be created in the current directory containing:
# - input.pdf  : original modified pdf document (with blank pages, to have a
#                number of pages which is a multiple of 4).
# - output.pdf : booklet
#
# usage: bash pdf-to-booklet.bash <pdfname>

get_n_pages() {
  local pdfname="$1"
  pdfinfo "${pdfname}" | grep Pages | sed 's/[^0-9]*//'
}

add_blank_pages() {
  local pdfname="$1"
  local n_pages=$2
  convert xc:none -page A4 blank.pdf
  for _ in $(seq 1 $[n_pages % 4]); do
    pdfunite "${pdfname}" blank.pdf "${pdfname}.bak"
    mv "${pdfname}.bak" "${pdfname}"
  done
}

get_num_pages() {
  local n=$1
  local i=$2
  echo "$n,$i,$[$i+1],$[$n-1],"
}

get_all_num_pages() {
  local n=$1
  local i=1
  local num_pages=''
  while [[ $[$n - $i] -gt 1 ]]; do
    num_pages=${num_pages}$(get_num_pages $n $i)
    n=$[n-2]
    i=$[i+2]
  done
  echo "${num_pages:0:${#num_pages}-1}"
}


if [[ ${FUNCNAME[0]} = "main" ]]; then

  echo "Creating booklet..."

  pdfname="$1"

  mkdir -pv output/
  cp -v "${pdfname}" output/input.pdf
  cd output/

  n_pages=$(get_n_pages input.pdf)
  add_blank_pages input.pdf ${n_pages}
  mod_4=$[${n_pages} % 4]
  [[ ${mod_4} -eq 0 ]] && n_pages_4=${n_pages} \
                       || n_pages_4=$[${n_pages} + 4 - ${mod_4}]
  num_pages=$(get_all_num_pages ${n_pages_4})
  pdfjam --landscape --nup 2 input.pdf "${num_pages}" -o output.pdf

  echo "...OK"
  
  fi