using several versions of ruby w/o rvm

rvm.sh

function r19 {
  switch-ruby $(brew --prefix)/Cellar/ruby/1.9.2-p0/bin
}

function r18 {
  switch-ruby $(brew --prefix)/Cellar/ruby-enterprise-edition/2010.02/bin
}

function switch-ruby {
  echo "using $1"
  export PATH=$(ruby -e 'puts ENV["PATH"].split(":").map { |p| p =~ /\bruby\b/ ? ARGV[0] : p }.uniq.join(":")' $1)
}