ratio.rb

#!/usr/bin/env ruby

# If you have a ratio of two numbers that you want to scale up or down you can 
# use this command line tool to provide the three known parts and it will 
# calculate the fourth.
#
# Usage
#
#   ratio a/b x/y
#
# Where a, b and y are known numbers and x is the one you want to calculate
# for. For example lets say you are buying a new HDTV. The ratio of a widescreen
# TV is 16:9. You have a home entertainment center that will only allow a TV
# a maximum of 50" wide. How tall will that TV be?
#
#   ratio 16/9 50/x
#   => 28.125
#
# So a TV screen that is 50" wide would be 28 1/8" tall.

if !ARGV.size == 2 || !ARGV.first.match('/') || !ARGV.last.match('/')
  puts "\nInvalid Ratio\n  ratio 16/9 33/x\n\n"
else
  top1, bottom1 = ARGV.first.split('/')
  top2, bottom2 = ARGV.last.split('/')
  if top1 == 'x'
    puts (top2.to_f * bottom1.to_f / bottom2.to_f).to_s
  elsif top2 == 'x'
    puts (top1.to_f * bottom2.to_f / bottom1.to_f).to_s
  elsif bottom1 == 'x'
    puts (top1.to_f * bottom2.to_f / top2.to_f).to_s
  elsif bottom2 == 'x'
    puts (top2.to_f * bottom1.to_f / top1.to_f).to_s
  end
end