ERLANG_OTP = OTP-20.0.4 include erlang.mk
Erlang.mk comes with integrated support for Kerl, a shell script that automates the downloading, building and installing of Erlang/OTP. It can be used to easily build a specific Erlang/OTP version (with or without custom build options) or maintain different versions side by side.
Erlang.mk uses the Git tags from Erlang/OTP to identify OTP versions. The most recent tag at the time of writing is OTP-20.0.4, which is a patch release of OTP-20.0. A patch release is a non-official release containing a few fixes on top of the official release.
Older versions used a slightly different versioning scheme and tag format, for example: OTP_R16B03. Beware though, there also was an OTP_R16B03-1 release that fixed a critical issue in the initial release.
The README file for all official Erlang/OTP releases can be found on erlang.org. To obtain information about patch releases when they are released you need to be subscribed to the erlang-questions mailing list.
Erlang.mk can use a specific version of Erlang/OTP when interacting with your project. This can be very useful when you are working with a team because you can define the version you need in the Makefile and Erlang.mk will ensure this version is used by everyone in your team.
To pin the version all you need to do is to set the ERLANG_OTP variable in your Makefile before including Erlang.mk. For example, to use OTP-20.0.4:
ERLANG_OTP = OTP-20.0.4 include erlang.mk
The next time you run make Erlang.mk will build and use the version you configured.
Note that there has been reports that this functionality is not compatible with the .ONESHELL feature from GNU Make.
Erlang.mk can automatically test your project against many different Erlang/OTP versions. This functionality is documented in the Continuous integration chapter.
All of the Kerl variables can be configured directly in the Makefile. All you need to do is to export them. For example, to change the installation directory for the Erlang/OTP versions managed by Kerl, you could add the following to your Makefile:
export KERL_INSTALL_DIR = $(CURDIR)/erlang
When configuring paths like this, always make sure to provide an absolute path in the value. Erlang.mk will NOT expand them automatically for you.
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