user-friendly (and quick-and-dirty) Ruby script to generate RAM disks on Mac OSX

make-osx-ram-disk.rb

BYTES_PER_SECTOR=512 # AFAIK this is constant for Mac OSX RAM disks
BYTES_PER_KILOBYTE=1024
BYTES_PER_MEGABYTE=1024*1024
BYTES_PER_GIGABYTE=1024*1024*1024

def bytes_to_sectors(bytes)
  sectors = (bytes / BYTES_PER_SECTOR).ceil
  return sectors
end

if 2 != ARGV.size
  puts('Usage: ruby make-ram-disk.rb NAME CAPACITY<kb|mb|gb>')
  puts('NAME may not contain spaces,')
  puts('CAPACITY must be a positive integer,')
  puts('and a valid CAPACITY unit suffix must be specified')
  exit(1)
end

name_arg = ARGV[0]
capacity_arg = ARGV[1]
capacity_arg_length = capacity_arg.length

if capacity_arg_length < 3
  puts("CAPACITY argument too short: must be at least three characters")
  exit(1)
end

name = name_arg
capacity = (capacity_arg[0...-2]).to_i # strip off two character unit suffix
capacity_unit = capacity_arg[capacity_arg_length-2..capacity_arg_length]

capacity_unit.downcase!

capacity_bytes = 0
case capacity_unit
when 'kb'
  capacity_bytes = capacity * BYTES_PER_KILOBYTE
when 'mb'
  capacity_bytes = capacity * BYTES_PER_MEGABYTE
when 'gb'
  capacity_bytes = capacity * BYTES_PER_GIGABYTE
else
  puts("invalid capacity unit suffix: valid suffixes are 'kb','mb','gb'")
  exit(1)  
end

puts("Creating RAM Disk: #{name} #{capacity} #{capacity_unit}")
sector_count = bytes_to_sectors(capacity_bytes)
puts("Sector Count: #{sector_count}")

def shellout(cmd)
  puts("Executing: #{cmd}")
  output = `#{cmd}`.strip
  puts("Output: #{output}")
  exit(1) unless $?.success?
  return output
end

mydev = shellout("hdiutil attach -nomount ram://#{sector_count}")
newfs_out = shellout("newfs_hfs -v #{name} #{mydev}")
mount_point = "/tmp/#{name}"
mkdir_out = shellout("mkdir -p #{mount_point}")
mount_out = shellout("mount -t hfs #{mydev} #{mount_point}")

puts('Done!')
exit(0)