Page order to make (or pdfjam command to turn a pdf file into) 4-up double-sided brochure ordered pages (to make two A6 folia per A4 page)

pdfbook4.rb

#!/usr/bin/env ruby

n = ARGV.shift.to_i
m = n
m = ((m / 8) + 1) * 8 if m % 8 != 0

p = (1..n).map(&:to_s) + ["{}"] * (m - n)
o = []

until p.empty? do
  t1 = []
  t2 = []

  t1.push(p.pop)
  t1.push(p.shift)
  t2.push(p.shift)
  t2.push(p.pop)

  t1.push(p.pop)
  t1.push(p.shift)
  t2.push(p.shift)
  t2.push(p.pop)

  o += t1
  o += t2
end

f = ARGV.shift

if f.nil?
  puts o.join(?,)
else
  puts "pdfjam --nup 2x2 -o #{File.basename(f, ".*")}-book.pdf #{f} #{o.join(?,)}"
end