dnd_dmg_calculator.rb

#!/usr/bin/env ruby
# USAGE: dnd.rb +0 0d0[+0] [0]
# e.g. dnd.rb +0 2d6
# or dnd.rb +5 2d6+6 2 (for 2 attacks per round e.g. flurry)

if ARGV.length < 2
  puts "ARGS = attk dmg"
  puts "e.g. +5 2d6+2"
  exit
end

atk = ARGV[0]
dmg = ARGV[1]
apr = ARGV[2].to_i # attacks per round
apr = 1 if apr == 0

unless atk =~ /[+-][0-9]+/
  puts "Cannot understand atk mod. Try something like +5 or -2"
  exit
end

unless dmg =~ /[0-9]+d[0-9]+([+-][0-9]+)*/
  puts "Cannot understand dmg mod. Try something like 2d6 or 3d4+6"
  exit
end

hitdie = 10.5 + atk.to_f

acs = [12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25]
print "AC  |"
acs.each do |ac|
  print "#{ac.to_s.rjust(6)} |"
end
puts

def hit_prob(atk, ac)
  (21 + atk.to_f - ac) / 20
end

print "HIT |"
acs.each do |ac|
  hitprob = hit_prob(atk, ac)
  if hitprob > 0
    print "#{sprintf('%.2f', hitprob).rjust(6)} |"
  end
end
puts


dien = dmg[/[0-9]+/].to_f
dice = dmg[/d[0-9]+/][1..-1].to_f
dmod = dmg[/[+-][0-9]+/].to_f

dmg = (dien * (dice.to_i / 2 + 0.5) + dmod) * apr

print "D/R |"
acs.each do |ac|
  hitprob = hit_prob(atk, ac)
  if hitprob > 0
    print "#{sprintf('%-.2f', hitprob*dmg.to_f).rjust(6)} |"
  else
    print "      |"
  end
end
puts

puts
puts "On a hit, avg dmg = #{dmg / apr}"