letter2a4

#!/usr/bin/env bash
set -e
# letter2a4 - Convert Letter-sized pdf to A4 with room for binding
# Usage: letter2a4 <letter.pdf>
# Required: poppler-utils(pdftocairo pdfunite) grep imagemagick(convert)
#  coreutils(file mktemp cd ls wc)

inp=$1
[[ -z $inp ]] && echo "Need Letter-sized pdf to convert to A4 for binding" && exit 1
[[ $inp = *^* ]] && echo "Need a filename that does not contain '^'" && exit 2
inp=$(readlink -e "$inp")
[[ -z $inp ]] && echo "File not found: $inp" && exit 3
[[ ${inp: -4} = .pdf ]] && in=${inp%.pdf} || in=$inp inp+=.pdf
i=${in##*/}

dir=$(mktemp -d)
cd "$dir"
pdftocairo "$inp" -png
p=$(ls "$dir/$i"-*.png |head -1)
m=$(ls "$dir/$i"-*.png |wc -l)
read w _ h <<<"$(file "$p" |grep -o '[0-9]* x [0-9]*')"

for p in "$i"-*[13579].png; do convert "$p" -resize 96%x100% -gravity east -extent ${w}x$h "$p.pdf"; done
((m>1)) && for p in "$i"-*[02468].png; do convert "$p" -resize 96%x100% -gravity west -extent ${w}x$h "$p.pdf"; done
pdfunite "$i"-*.png.pdf "$in".png.pdf
rm -r -- "$dir"