rb_switch.rb

#!/usr/bin/env ruby
# coding: utf-8

require 'fileutils'

PATH     = "/Users/uk/local/bin"
RUBY_VER = ["1.9.2", "1.8.7"]
CMD      = ["ruby", "irb", "gem"]

version = ARGV.first
exit unless RUBY_VER.include? version

def remove_symbolic_link(version)
  FileUtils.rm(CMD.map{|c| PATH + "/#{c}"})
end

def create_symbolic_link(version)
  CMD.each do |c|
    original = PATH + "/#{c}-#{version}"
    link = PATH + "/#{c}"
    FileUtils.symlink(original, link)
  end
end

remove_symbolic_link(version)
create_symbolic_link(version)