gistfile1.txt

#!/usr/bin/env ruby1.8

# Method chosen carefully -- avoiding symbols

def unshift env, value
  ENV[env] = ENV[env].to_s.split(':').unshift(value).join(':')
end

def read
  homedir = '/home/rubygems'

  gem = "#{homedir}/home"
  unshift 'GEM_HOME', "#{homedir}/home"
  unshift 'PATH', "#{homedir}/bin:#{gem}/bin"
  
  lib = "#{homedir}/lib"
  unshift 'RUBYLIB', lib

  program = ARGV.shift

  real_path = (program =~ /\//) ? program : `which #{program}`.chomp
  possible_shebang = File.read(real_path, 1024).split("\n").first

  if possible_shebang =~ /^#!/
    parts = possible_shebang.split
    parts.shift if parts.first =~ /env$/
    if parts.first =~ /ruby(\d+(\.\d+)*)?$/
      # Found a Ruby file. Clean up and return.
      [:unshift, :read].each do |m|
        self.class.send :remove_method, m
      end
      $:.unshift lib
      return $0 = real_path
    end
  end

  # Not a Ruby file, then
  exec program, *ARGV
end

# If we get a return value (program didn't exit), we execute that file
# in the current Ruby interpreter. Because of the names of the above methods,
# we actually have ZERO footprint beyond changing environment variables
# (and changing which interpreter to use).
load read