Lightweigh version of rvm.

Light weight rvm

#!/usr/bin/env ruby

require 'pp'
require 'pathname'

search_paths = ['/usr/local']

Conf_file = "#{ENV['HOME']}/.lrvm"

def write_path(path)
  File.open(Conf_file, 'w') do |fd|
    fd.write(path.to_s)
  end
end

def full_path
  path = (File.exist?(Conf_file)) ? "#{File.read(Conf_file)}:#{ENV['PATH']}" : ENV['PATH']
  path.split(/:/).uniq.join(":")
end

def default_ruby_path
  ENV['PATH'].split(/:/).map { |p| Pathname.new(p) }.detect do |path|
    path.join("ruby").exist? unless path.fnmatch("*ruby*")
  end.to_s
end

def find_ruby_paths(paths)
  paths.inject([]) do |all_dirs, path|
    all_dirs.tap do |_all_dirs|
      _all_dirs << Pathname.new(path).entries.inject([]) do |dirs,dir|
        dirs.tap do |_dirs|
          _dirs << dir.expand_path(path).join("bin") if dir.fnmatch("*ruby*")
        end
      end
    end
  end.flatten
end

ruby_paths = find_ruby_paths(search_paths)
ruby_paths.insert(0, default_ruby_path)

ruby_paths.each_with_index do |path,n|
  STDERR.puts "[%i] %s" % [n, path]
end

STDIN.each do |input|
  index = Integer(input.strip) rescue nil
  if index && index < ruby_paths.size
    write_path(ruby_paths[index])
    puts "PATH=#{full_path}"
    exit
  else
    puts "Please enter a number between 0 and #{ruby_paths.size - 1}"
  end
end

STDERR.puts "Ok doing nothing as asked"

I personally like to install ruby versions system wide so this script looks at what versions are installed (it currently looks in /usr/local/bin but it's easy to add more) and prints the different options for you to select. It adds the path to $HOME/.lrvm so you can use it for other purposes such as adding the version to your prompt. You can then eval the output into your current environment:

eval $(/path/to/lrvm)

You can add this to your shell config file (assumes sh compatible):

alias lrvm='eval $(/path/to/lrvm)'

To add the version of ruby to your prompt (zsh):

precmd () { ruby_version=$(ruby -v | awk '{print $2}') }
PROMPT='%m:%/-{${ruby_version}}'