I was a long time user of RVM for installing and switching Rubies. It made my life pretty easy even as I listened to others struggle with it. I was a little uncomfortable putting other things like project-specific environment variables in my .rvmrc files. It seemed dirty, but it worked and I rolled with it for many years.

Eventually, I tried something different. I’d been sold on the idea of using multiple, simpler tools together. Here’s the result.

Installing a Ruby: ruby-install

> brew install ruby-install
> ruby-install ruby-2.2

Got me the Ruby I wanted. “Too simple,” I thought. “Now I won’t be able to say I want to use that version.”

Use a Ruby: chruby

> brew install chruby
> chruby
   ruby-2.2.4

And then chruby spat out a list of installed Rubies.

OK.

> chruby ruby-2.2.4
> chruby
 * ruby-2.2.4
> ruby --version
ruby 2.2.4p230 (2015-12-16 revision 53155) [x86_64-darwin15]

“Hunh,” thinks I. chruby will by default find Rubies installed in the default directory used by ruby-install: /opt/rubies/ and ~/.rubies/.

“OK. But now I have to run that for each project to get the Ruby the project needs.”

Project-Specific Environments: direnv

Enter direnv.

> brew install direnv

Then create an .envrc file in a project root directory with the appropriate commands for the project. It can be made pretty convenient by adding the following function to a .direnvrc file in your HOME directory.

# add to ~/.direnvrc
use_ruby() {
  # enable the chruby command in an environment
  source /usr/local/opt/chruby/share/chruby/chruby.sh

  # desired Ruby version as first parameter
  local ver=$1

  # if version not given as parameter and there is a .ruby-version file, get
  # version from the file
  if [[ -z $ver ]] && [[ -f .ruby-version ]]; then
    ver=$(cat .ruby-version)
  fi

  # if the version still isn't set, error cause we don't know what to do
  if [[ -z $ver ]]; then
    echo Unknown ruby version
    exit 1
  fi

  # switch to the desired ruby version
  chruby $ver

  # Sets the GEM_HOME environment variable to `$PWD/.direnv/ruby/RUBY_VERSION`.
  # This forces the installation of any gems into the project’s sub-folder. If
  # you’re using bundler it will create wrapper programs that can be invoked
  # directly instead of using the `bundle exec` prefix.
  layout_ruby
}

Thanks to Steve Tooke for most of the above.

So one of my projects is a Rails app. It’s .envrc looks like:

# .envrc for a Rails project
export RUBY_GC_MALLOC_LIMIT=90000000
export RUBY_GC_HEAP_FREE_SLOTS=200000

use ruby 2.2.4

This sets some environment variables suitable for testing and switches my Ruby environment around. I get Ruby version 2.2.4 and GEM_HOME, GEM_PATH, and GEM_ROOT adjusted to bring in global gems from the 2.2.4 install and project-specific gems from <project-root>/.direnv/ruby thanks to direnv’s layout ruby feature. I recommend adding .direnv to your project’s .gitignore.

Bonus Round - Chef DK!

I use Chef and the recommended way to install Chef on a development workstation is to install the Chef DK. Chef DK includes its own embedded Ruby and gem environment and chruby knows nothing about it. We can use direnv to twiddle the environment for Chef projects.

# add to ~/.direnvrc
use_chefdk() {
  EXPANDED_HOME=`expand_path ~`

  # Override the GEM environment

  log_status "Overriding default Ruby environment to use ChefDK"
  RUBY_ABI_VERSION=`ls /opt/chefdk/embedded/lib/ruby/gems/`
  export GEM_ROOT="/opt/chefdk/embedded/lib/ruby/gems/$RUBY_ABI_VERSION"
  export GEM_HOME="$EXPANDED_HOME/.chefdk/gem/ruby/$RUBY_ABI_VERSION"
  export GEM_PATH="$EXPANDED_HOME/.chefdk/gem/ruby/$RUBY_ABI_VERSION:/opt/chefdk/embedded/lib/ruby/gems/$RUBY_ABI_VERSION"

  # Ensure ChefDK and its embedded tools are first in the PATH

  log_status "Ensuring ChefDK and it's embedded tools are first in the PATH"

  PATH_add $EXPANDED_HOME/.chefdk/gem/ruby/$RUBY_ABI_VERSION/bin/
  PATH_add /opt/chefdk/embedded/bin
  PATH_add /opt/chefdk/bin
}

Thanks to Seth Chisamore for the Chef DK function.

Now my .envrc files in Chef projects have a line like this:

# .envrc in a Chef project
use chefdk

It’s working for now and I can happily switch between Chef DK projects and projects needing their own Rubies (e.g. Rails sites).