eyruby_switch.rb

#!/usr/bin/env ruby

source_dir = nil
if ARGV[0] == 'ree'
  source_dir = lambda { |binary| "/opt/ruby-enterprise-1.8.6-20090610/bin/#{binary}" }
elsif ARGV[0] == 'mri'
  source_dir = lambda { |binary| "/usr/bin/#{binary}18" }
else
  raise ArgumentError.new("acceptable args are 'mri' and 'ree'")
end

%w[erb gem irb rackup rails rake rdoc ri ruby testrb].each do |binary|
  cmd = "sudo rm /usr/bin/#{binary}"
  puts cmd
  puts `#{cmd}`
 
  cmd = "sudo ln -s #{source_dir.call(binary)} /usr/bin/#{binary}"
  puts cmd
  puts `#{cmd}`
end