[[getting_started]]
== Getting started

This chapter explains how to get started using Erlang.mk.

=== Creating a folder for your project

The first step is always to create a new folder that will
contain your project.

[source,bash]
$ mkdir hello_joe
$ cd hello_joe

Most people tend to put all their projects side by side in
a common folder. We recommend keeping an organization similar
to your remote repositories. For example, for GitHub users,
put all your projects in a common folder with the same name
as your username. For example '$HOME/ninenines/cowboy' for
the Cowboy project.

=== Downloading Erlang.mk

At the time of writing, Erlang.mk is unlikely to be present
in your Erlang distribution, or even in your OS packages.

The next step is therefore to download it:

[source,bash]
$ wget https://erlang.mk/erlang.mk

Or:

[source,bash]
$ curl -O https://erlang.mk/erlang.mk

Alternatively, just https://erlang.mk/erlang.mk[click on this link].

Make sure you put the file inside the folder we created previously.

=== Getting started with OTP applications

An OTP application is an Erlang application that has a supervision
tree. In other words, it will always have processes running.

This kind of project can be automatically generated by Erlang.mk.
All you need to do is use the `bootstrap` target:

[source,bash]
$ make -f erlang.mk bootstrap

Something similar to the following snippet will then appear
on your screen:

[source,bash]
----
git clone https://github.com/ninenines/erlang.mk .erlang.mk.build
Cloning into '.erlang.mk.build'...
remote: Counting objects: 4035, done.
remote: Compressing objects: 100% (12/12), done.
remote: Total 4035 (delta 8), reused 4 (delta 4), pack-reused 4019
Receiving objects: 100% (4035/4035), 1.10 MiB | 784.00 KiB/s, done.
Resolving deltas: 100% (2442/2442), done.
Checking connectivity... done.
if [ -f build.config ]; then cp build.config .erlang.mk.build; fi
cd .erlang.mk.build && make
make[1]: Entering directory '/home/essen/tmp/hello_joe/.erlang.mk.build'
awk 'FNR==1 && NR!=1{print ""}1' core/core.mk index/*.mk core/index.mk core/deps.mk plugins/protobuffs.mk core/erlc.mk core/docs.mk core/test.mk plugins/asciidoc.mk plugins/bootstrap.mk plugins/c_src.mk plugins/ci.mk plugins/ct.mk plugins/dialyzer.mk plugins/edoc.mk plugins/elvis.mk plugins/erlydtl.mk plugins/escript.mk plugins/eunit.mk plugins/relx.mk plugins/shell.mk plugins/triq.mk plugins/xref.mk plugins/cover.mk \
	| sed 's/^ERLANG_MK_VERSION = .*/ERLANG_MK_VERSION = 1.2.0-642-gccd2b9f/' > erlang.mk
make[1]: Leaving directory '/home/essen/tmp/hello_joe/.erlang.mk.build'
cp .erlang.mk.build/erlang.mk ./erlang.mk
rm -rf .erlang.mk.build
----

This is Erlang.mk bootstrapping itself. Indeed, the file you
initially downloaded contains nothing more than the code needed
to bootstrap. This operation is done only once. Consult the
xref:updating[Updating Erlang.mk] chapter for more
information.

Of course, the generated project can now be compiled:

[source,bash]
$ make

Cheers!

=== Getting started with OTP libraries

An OTP library is an Erlang application that has no supervision
tree. In other words, it is nothing but modules.

This kind of project can also be generated by Erlang.mk, using
the `bootstrap-lib` target:

[source,bash]
$ make -f erlang.mk bootstrap-lib

Erlang.mk will once again bootstrap itself and generate all
the files for your project. You can now compile it:

[source,bash]
$ make

Enjoy!

=== Getting started with OTP releases

An OTP release is the combination of the Erlang RunTime System (ERTS)
along with all the libraries and files that your node will need
to run. It is entirely self contained, and can often be sent as-is
to your production system and run without any extra setup.

Erlang.mk can of course bootstrap your project to generate releases.
You can use the `bootstrap-rel` target for this purpose:

[source,bash]
$ make bootstrap-rel

This target can be combined with `bootstrap` or `bootstrap-lib` to
create a project that will build a release:

[source,bash]
$ make -f erlang.mk bootstrap-lib bootstrap-rel

It is often very useful to keep the top-level project for
commands useful during operations, and put the components
of the system in separate applications that you will then
depend on. Consult the xref:deps[Packages and dependencies]
chapter for more information.

When you run `make` from now on, Erlang.mk will compile your
project and build the release:

[source,bash]
$ make
 APP    hello_joe.app.src
 GEN    distclean-relx-rel
 GEN    /home/essen/tmp/hello_joe/relx
===> Starting relx build process ...
===> Resolving OTP Applications from directories:
          /home/essen/tmp/hello_joe/ebin
          /usr/lib/erlang/lib
          /home/essen/tmp/hello_joe/deps
===> Resolved hello_joe_release-1
===> Including Erts from /usr/lib/erlang
===> release successfully created!

The first time you run this command, Erlang.mk will download
_relx_, the release building tool. So don't worry if you see
more output than above.

If building the release is slow, no need to upgrade your
hardware just yet. Just consult the xref:relx[Releases]
chapter for various tips to speed up build time during
development.

You can start the release using the './_rel/hello_joe_release/bin/hello_joe_release'
script, or simply run `make run`. The latter will also compile
your project and build the release if it wasn't already:

[source,bash]
----
$ make run
 APP    hello_joe.app.src
 GEN    distclean-relx-rel
===> Starting relx build process ...
===> Resolving OTP Applications from directories:
          /home/essen/tmp/hello_joe/ebin
          /usr/lib/erlang/lib
          /home/essen/tmp/hello_joe/deps
===> Resolved hello_joe_release-1
===> Including Erts from /usr/lib/erlang
===> release successfully created!
Exec: /home/essen/tmp/hello_joe/_rel/hello_joe_release/erts-7.0/bin/erlexec -boot /home/essen/tmp/hello_joe/_rel/hello_joe_release/releases/1/hello_joe_release -boot_var ERTS_LIB_DIR /home/essen/tmp/hello_joe/_rel/hello_joe_release/erts-7.0/../lib -env ERL_LIBS /home/essen/tmp/hello_joe/_rel/hello_joe_release/releases/1/lib -config /home/essen/tmp/hello_joe/_rel/hello_joe_release/releases/1/sys.config -args_file /home/essen/tmp/hello_joe/_rel/hello_joe_release/releases/1/vm.args -- console
Root: /home/essen/tmp/hello_joe/_rel/hello_joe_release
/home/essen/tmp/hello_joe/_rel/hello_joe_release
heart_beat_kill_pid = 16389
Erlang/OTP 18 [erts-7.0] [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false]

Eshell V7.0  (abort with ^G)
(hello_joe@127.0.0.1)1> 
----

Simple as that!

=== Getting started from scratch

If you already have an application, or you want to have full
control over what files will be created, you can setup Erlang.mk
manually.

Erlang.mk is very easy to setup: all that you need to do is to
create a folder, put Erlang.mk in it, and write a one line
Makefile containing:

[source,make]
include erlang.mk

For a step by step:

[source,bash]
----
$ mkdir hello_joe
$ cd hello_joe
$ curl https://erlang.mk/erlang.mk -o erlang.mk
$ echo "include erlang.mk" > Makefile
$ make
----

From that point onward you can create an `src/` folder or start
using templates.

=== Using spaces instead of tabs

Erlang.mk defaults to tabs when creating files from templates.
This is in part because of a personal preference, and in part
because it is much easier to convert tabs to spaces than the
opposite.

Use the `SP` variable if you prefer spaces. Set it to the number
of spaces per indentation level you want.

For example, if you prefer two spaces per indentation level:

[source,bash]
$ make -f erlang.mk bootstrap SP=2

When you bootstrap the project initially, the variable automatically
gets added to the Makefile, so you only need to provide it when
you get started.

=== Using templates

It is no secret that Erlang's OTP behaviors tend to have some
boilerplate. It is rarely an issue of course, except when
creating new modules. That's why Erlang.mk not only comes with
templates for generating projects, but also individual modules!

You can list all available templates with the `list-templates`
target:

[source,bash]
$ make list-templates
Available templates: cowboy_http cowboy_loop cowboy_rest cowboy_ws gen_fsm gen_server ranch_protocol supervisor

To generate a module, let's say a `gen_server`, all you need to
do is to call `make new` with the appropriate arguments:

[source,bash]
$ make new t=gen_server n=my_server

This will create a module located in 'src/my_server.erl'
using the `gen_server` template.

This module is automatically compiled the next time you run
`make`:

[source,bash]
$ make
 ERLC   my_server.erl
 APP    hello_joe.app.src

All that's left to do is to open it in your favorite editor
and make it do something!

=== Hiding Erlang.mk from git

Erlang.mk is a large text file. It can easily take a large part of
a `git diff` or a `git grep` command. You can avoid this by telling
Git that 'erlang.mk' is a binary file.

Add this to your '.gitattributes' file. This is a file that you
can create at the root of your repository:

----
erlang.mk -diff
----

The 'erlang.mk' file will still appear in diffs and greps, but
as a binary file, meaning its contents won't be shown by default
anymore.

=== Getting help

During development, if you don't remember the name of a target,
you can always run `make help`:

[source,bash]
----
$ make help
erlang.mk (version 1.2.0-642-gccd2b9f) is distributed under the terms of the ISC License.
Copyright (c) 2013-2016 Loïc Hoguin <essen@ninenines.eu>

Usage: [V=1] make [target]...

Core targets:
  all           Run deps, app and rel targets in that order
  app           Compile the project
  deps          Fetch dependencies (if needed) and compile them
  search q=...  Search for a package in the built-in index
  rel           Build a release for this project, if applicable
  docs          Build the documentation for this project
  install-docs  Install the man pages for this project
  check         Compile and run all tests and analysis for this project
  tests         Run the tests for this project
  clean         Delete temporary and output files from most targets
  distclean     Delete all temporary and output files
  help          Display this help and exit
  erlang-mk     Update erlang.mk to the latest version

Bootstrap targets:
  bootstrap          Generate a skeleton of an OTP application
  bootstrap-lib      Generate a skeleton of an OTP library
  bootstrap-rel      Generate the files needed to build a release
  new t=TPL n=NAME   Generate a module NAME based on the template TPL
  list-templates     List available templates
...
----

This guide should provide any other answer. If not, please
open a ticket on https://github.com/ninenines/erlang.mk/issues[the official repository]
and we will work on improving the guide.

Commercial support is available through Nine Nines. Please contact
Loïc Hoguin by sending an email to mailto:contact@ninenines.eu[].
