9 Development & Deployment

9.2 Working with Kerl

These instructions were adopted from the kerl README. There's more good stuff on that page.

9.2.1 Installation

Installation is a piece of cake:

$ curl -O https://raw.github.com/spawngrid/kerl/master/kerl
$ mv kerl /usr/local/bin/
$ chmod a+x /usr/local/bin/kerl

9.2.2 Poking Around

The first thing you're going to want to do is see what kerl can do:

$ kerl

Which gives:

kerl: build and install Erlang/OTP
usage: /usr/local/bin/kerl <command> [options ...]

  <command>       Command to be executed

Valid commands are:
  build    Build specified release or git repository
  install  Install the specified release at the given location
  deploy   Deploy the specified installation to the given host and location
  update   Update the list of available releases from erlang.org
  list     List releases, builds and installations
  delete   Delete builds and installations
  active   Print the path of the active installation
  status   Print available builds and installations
  prompt   Print a string suitable for insertion in prompt
  cleanup  Remove compilation artifacts (use after installation)

Let's see what releases are available:

$ kerl list releases

This will give you output like the following:

R10B-0 R10B-10 R10B-1a R10B-2 R10B-3 R10B-4 R10B-5 R10B-6 R10B-7 R10B-8
R10B-9 R11B-0 R11B-1 R11B-2 R11B-3 R11B-4 R11B-5 R12B-0 R12B-1 R12B-2
R12B-3 R12B-4 R12B-5 R13A R13B R13B01 R13B02-1 R13B02 R13B03 R13B04 R14A
R14B R14B01 R14B02 R14B03 R14B04 R15B R15B01 R15B02
R15B02_with_MSVCR100_installer_fix R15B03-1
R15B03 R16A_RELEASE_CANDIDATE R16B
Run "/usr/local/bin/kerl update releases" to update this list from erlang.org

So many choices! Time to play >:-)

9.2.3 Installing an Erlang

We've see what releases are available. To install one, we need to:

Choose a release, and
Come up with a name for out installation of it.

We're going to install the almost-venerable R15B03 as our primary Erlang:

$ kerl build R15B03 erlang-15b03

This will take a few minutes... time for a bio break.

Note that kerl supports passing options to the build so you can enable/disable various features. For more details, see the github README for kerl.

Once that's done, it's time to actually install it. Here, we use the name we chose when we built our particular Erlang. In this case, erlang-15b03:

$ kerl install erlang-15b03 /opt/erlang/R15B03

Careful: if you leave off the path, kerl will install Erlang in your current directory.

Before we go into the details on using a kerl-based Erlang, let's install another version.

9.2.4 Running Multiple Erlang Versions

Let's say we also want to develop against R16B; let's set that up too:

$ kerl build R16B erlang-R16B
$ kerl install erlang-R16B /opt/erlang/R16B

Now that we have more than one Erlang installed, the next command will be useful:

$ kerl list installations

Which will give you:

erlang-15b03 /opt/erlang
erlang-R16B /opt/erlang

Now for a sanity check:

$ which erl

If you don't have any other Erlangs installed, that should have returned nothing.

Let's try these out now:

$ . /opt/erlang/R15B03/activate
$ erl -eval 'erlang:display(erlang:system_info(otp_release)), halt().'  -noshell
"R15B03"
$ kerl_deactivate
$ . /opt/erlang/R16B/activate
$ erl -eval 'erlang:display(erlang:system_info(otp_release)), halt().'  -noshell
"R16B"

We're all set!

9.2.5 Deleting Erlang Versions

If for any reason you should want to remove a kerl installation of Erlang, you will need to do the following:

$ kerl delete installation /opt/erlang/old-or-bad-version

You can do something similar for builds:

$ kerl delete build my-old-build

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