Linux and OS X Shared Memory Calculator

shm.rb

#!/usr/bin/env ruby

def halt
  puts "----------------------------------"
  puts "             Usage                "
  puts "----------------------------------"
  puts "./shm.rb <size> <units>"
  puts "\tsize  = integer > 0"
  puts "\tunits = MB or GB"
  exit
end

if ARGV.size != 2
  halt
end

size  = ARGV[0].to_i
units = ARGV[1]

if size <= 0
  halt
end

if units != "MB" && units != "GB"
  halt
end

case units
  when "MB"
    size = size * 1024 * 1024;
  when "GB"
    size = size * 1024 * 1024 * 1024;
end

puts "----------------------------------"
puts "             Linux                "
puts "----------------------------------"
puts "kernel.shmmax     = #{size}"
puts "kernel.shmall     = #{size / 4096}"
puts

puts "----------------------------------"
puts "             OS X                 "
puts "----------------------------------"
puts "kern.sysv.shmmax  = #{size}"
puts "kern.sysv.shmmin  = 1"
puts "kern.sysv.shmmni  = 32"
puts "kern.sysv.shmseg  = 8"
puts "kern.sysv.shmall  = #{size / 4096}"
puts