From: Kaspar Schiess <eule@...>
Date: 2009-08-18T15:31:10+09:00
Subject: Re: ruby 1.9 side by side with 1.8

> and i can switch ruby versions with select_ruby script that updates a
> symbolic link that points to the active version.

Updating a single symbolic link wasn't enough here - I wanted to update 
gem binaries as well. Here's what I use (and I am sure you can deduce 
further details from the script)...

kaspar

--------------

#!/usr/local/share/ruby19/bin/ruby

def base_path
   '/usr/local/share/'
end
def bin_dir(version)
   File.join(base_path, version, 'bin')
end
def lib_dir(version)
   File.join(base_path, version, 'lib')
end

def replace_symlink(source, dest)
   if !File.exists?(dest) || File.symlink?(dest)
     print "[#{File.basename(dest)}] "
     `sudo ln -nsf #{source} #{dest}`
   end
end

# Iterates over binaries in version.
#
def all_binary_links(version) # yield: binary_path, symlink_path
   Dir[File.join(bin_dir(version), '*')].each do |binary_path|
     binary_name = File.basename(binary_path)
     yield binary_path, File.join('/usr/bin', binary_name)
   end
end

def switch_to(ruby_version, old_version)
   # Remove current (old) symlinks
   puts "Removing old links..."
   all_binary_links(old_version) do |bin_path, link_path|
     print '.'
     `sudo rm #{link_path} 2>/dev/null`
   end
   puts

   puts "Symlinking new version..."
   all_binary_links(ruby_version) do |bin_path, link_path|
     replace_symlink(bin_path, link_path)
   end
   puts

   # Symlink /lib
   replace_symlink(
     lib_dir(ruby_version),
     '/usr/lib/ruby')
   puts
end

case ARGV.first
   when /19/
     switch_to :ruby19, :ruby18
   when /18/
     switch_to :ruby18, :ruby19
else
   puts "Run with either '19' or '18' to switch to the given ruby 
version..."
end