The following is a short example of building a simple command line utility to read and write objects to Riak.

Items covered:

• Rebar
• Riak Erlang Client

curl -O -L https://github.com/downloads/basho/rebar/rebar
chmod a+x rebar

./rebar -c

Configuration options, such as dependencies, are specified in the rebar.config file.

cat > rebar.config
{deps, [
 {riakc, "1.0.*",
  {git, "git://github.com/basho/riak-erlang-client.git", "HEAD"}}
]}.

You can read about the various other rebar config options here.

./rebar get-deps

You'll notice that rebar has also pulled down the Erlang Protobuffs application which the Riak Erlang Client depends on.

./rebar create-app appid=sample_riak_erlang_client_app skip_deps=true

Note the use of the command line option skip_deps=true. By default commands are executed on the current application and all dependencies. If the skip_deps option were not specified the sample_riak_erlang_client_app would have been created in our dependencies as well as in our project directory.

For this project we didn't actually need to create an application. The rebar application template (create-app) provides an .app.src file which is required for rebar to compile the project. This file is known as the application resource file. More information regarding this file can be found here.

The file looks as follows:

cat src/sample_riak_erlang_client_app.app.src 
{application, sample_riak_erlang_client_app,
  [
    {description, ""},
    {vsn, "1"},
    {registered, []},
    {applications, [
              kernel,
              stdlib
             ]},
    {mod, { sample_riak_erlang_client_app_app, []}},
    {env, []}
]}.

./rebar create template=simplemod \
modid=sample_riak_erlang_client_app skip_deps=true

Unfortunately, templates are not documented very well at the moment. One needs to review the template source to determine the valid variables.

Note the use of skip_deps=true again.

We'll be building an escript compatible module for our command line tool. Documentation regarding escript is available here.

Escript modules are fairly simple, command line arguments are passed to the main/1 function in the module. Our module simply needs to export a main/1 function.

For rebar to correctly build the escript we need to add an option to our rebar.config.

echo "{escript_incl_apps, [riakc, protobuffs]}." >> rebar.config

This is a very simple command line tool to provide basic read and write access to Riak. Two commands, get and put, will be supported.

Examples:

sample_riak_erlang_client_app put bucket key value
sample_riak_erlang_client_app get bucket key

# Compile
./rebar compile

# Build escript
./rebar escriptize skip_deps=true

# Run
./sample_riak_erlang_client_app get bucket key

# Compile
./rebar compile

# Build escript
./rebar escriptize skip_deps=true

# Run
./sample_riak_erlang_client_app put bucket key "hello world"

• Accept host and port options
• Accept r, w, and dw options