== Installation

This chapter explains how to setup your system in
order to use Erlang.mk.

=== On Unix

Erlang.mk requires GNU Make to be installed. GNU Make 3.81
or later is required. GNU Make 4.1 or later is recommended,
as this is the version Erlang.mk is developed on.

Some functionality requires that Autoconf 2.59 or later be
installed, in order to compile Erlang/OTP. Erlang/OTP may
have further requirements depending on your needs.

Erlang.mk currently requires Erlang/OTP to be installed in
order to compile Erlang projects.

Some packages may require additional libraries.

=== On Windows

Erlang.mk can be used on Windows inside an MSYS2 environment.
Cygwin, MSYS (the original) and native Windows (both Batch
and PowerShell) are currently not supported.

The rest of this section details how to setup Erlang/OTP and
MSYS2 in order to use Erlang.mk.

==== Installing Erlang/OTP

Erlang.mk requires Erlang/OTP to be installed. The OTP team
provides binaries of Erlang/OTP for all major and minor releases,
available from the http://www.erlang.org/download.html[official download page].
It is recommended that you use the 64-bit installer unless
technically impossible. Please follow the instructions from
the installer to complete the installation.

The OTP team also provides a short guide to
http://www.erlang.org/download.html[installing Erlang/OTP on Windows]
if you need additional references.

You can install Erlang/OTP silently using the `/S` switch
on the command line:

----
C:\Users\essen\Downloads> otp_win64_18.0.exe /S
----

==== Installing MSYS2

The only supported environment on Windows is MSYS2. MSYS2 is
a lightweight Unix-like environment for Windows that comes
with the Arch Linux package manager, `pacman`.

The MSYS2 project provides a http://msys2.github.io[one click installer]
and instructions to set things up post-installation.

It is currently not possible to use the installer silently.
Thankfully, the MSYS2 project provides an archive that can
be used in lieu of the installer. The archive however requires
_7zip_ to decompress it.

First, download the
http://sourceforge.net/projects/msys2/files/Base/x86_64/msys2-base-x86_64-20150512.tar.xz/download[MSYS2 base archive]
and extract it under 'C:\'. Assuming you downloaded the
archive as 'msys2.tar.xz' and put it in 'C:\', you can
use the following commands to extract it:

----
C:\> 7z x msys2.tar.xz
C:\> 7z x msys2.tar > NUL
----

Then you can run the two commands needed to perform the
post-installation setup:

----
C:\> C:\msys64\usr\bin\bash -lc "pacman --needed --noconfirm -Sy bash pacman pacman-mirrors msys2-runtime"
C:\> C:\msys64\usr\bin\bash -lc "pacman --noconfirm -Syu"
----

==== Installing the required MSYS2 packages

After following these instructions, you can install GNU Make,
Git and any other required softwares. From an MSYS2 shell,
you can call `pacman` directly:

[source,bash]
$ pacman -S git make

You can use `pacman -Ss` to search packages. For example,
to find all packages related to GCC:

[source,bash]
$ pacman -Ss gcc

If you are going to compile C/C++ code, you will need to
install this package, as Erlang.mk cannot use the normal
"gcc" package:

[source,bash]
$ pacman -S mingw-w64-x86_64-gcc

You can also run commands under the MSYS2 environment from
the Windows command line or batch files. This command will
install GNU Make and Git:

----
C:\> C:\msys64\usr\bin\bash -lc "pacman --noconfirm -S git make"
----

You can use similar `bash` commands if you need to run programs
inside the MSYS2 environment from a batch file.

==== Gotchas

While most of the basic functionality will just work, there are
still some issues. Erlang.mk needs to be fixed to pass the
right paths when running Erlang scripts. We are working on it.
Erlang.mk is fully tested on both Linux and Windows, but is
lacking tests in the areas not yet covered by this guide,
so expect bugs to be fixed as more tests are added.
