pts2mm.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

# Usage: pdfinfo input.pdf | ./pts2mm.rb

# This script converts "595.276 x 841.89 pts" to "210.00 x 297.00".
# 72pt = 1inch = 25.4 mm

print STDIN.read.scan(/(\S+) x (\S+)/).map { _1.map(&:to_f).map { |j| '%.2f' % (j / 72 * 25.4) }.join(' x ') + "\n" }.join

# Note:
#   I created this script to calculate the scale for converting
#   gimp-generated PDF to A4-sized PDF using pdfjam. However, I
#   noticed that pdfjam scales the input PDF automatically to fit the
#   output paper size. So the scale factor is relative to the
#   automatically fitted size, which means that the scale factor of
#   1.0 indicates a full-size fit. Note that the input content is
#   positioned at the center of the output PDF.
#
#   `pdfjam --suffix converted --paper a4paper --scale 1.0 input.pdf`