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Friday, 8 July 2016


Erlang build tool that makes it easy to compile and test Erlang applications

  1. What is Rebar3?
  2. Why Rebar3?
  3. Should I Use Rebar3?
  4. Getting Started
  5. Documentation
  6. Features
  7. Migrating from rebar2
  8. Additional Resources

What is Rebar3

Rebar3 is an Erlang tool that makes it easy to create, develop, and release Erlang libraries, applications, and systems in a repeatable manner.
Rebar3 will:
  • respect and enforce standard Erlang/OTP conventions for project structure so they are easily reusable by the community;
  • manage source dependencies and Erlang packages while ensuring repeatable builds;
  • handle build artifacts, paths, and libraries such that standard development tools can be used without a headache;
  • adapt to projects of all sizes on almost any platform;
  • treat documentation as a feature, and errors or lack of documentation as a bug.
Rebar3 is also a self-contained Erlang script. It is easy to distribute or embed directly in a project. Tasks or behaviours can be modified or expanded with a plugin system flexible enough that even other languages on the Erlang VM will use it as a build tool.

Why Rebar3

Rebar3 is the spiritual successor to rebar 2.x, which was the first usable build tool for Erlang that ended up seeing widespread community adoption. It however had several shortcomings that made it difficult to use with larger projects or with teams with users new to Erlang.
Rebar3 was our attempt at improving over the legacy of Rebar 2.x, providing the features we felt it was missing, and to provide a better environment in which newcomers joining our teams could develop.

Should I use Rebar3?

If your main language for your system is Erlang, that you value repeatable builds and want your various tools to integrate together, we do believe Rebar3 is the best experience you can get.

Getting Started

getting started guide is maintained on the official documentation website, but installing rebar3 can be done by any of the ways described below
Nightly compiled version:
$ wget && chmod +x rebar3
From Source (assuming you have a full Erlang install):
$ git clone
$ cd rebar3
$ ./bootstrap
Stable versions can be obtained from the releases page.
The rebar3 escript can also extract itself with a run script under the user's home directory:
$ ./rebar3 local install
===> Extracting rebar3 libs to ~/.cache/rebar3/lib...
===> Writing rebar3 run script ~/.cache/rebar3/bin/rebar3...
===> Add to $PATH for use: export PATH=$PATH:~/.cache/rebar3/bin
To keep it up to date after you've installed rebar3 this way you can use rebar3 local upgrade which fetches the latest nightly and extracts to the same place as above.
Rebar3 may also be available on various OS-specific package managers such as FreeBSD Ports. Those are maintained by the community and Rebar3 maintainers themselves are generally not involved in that process.
If you do not have a full Erlang install, we using erln8 or kerl. For binary packages use those provided by Erlang Solutions, but be sure to choose the "Standard" download option or you'll have issues building projects.


Rebar3 documentation is maintained on


Rebar3 supports the following features or tools by default, and may provide many others via the plugin ecosystem:
Command compositionRebar3 allows multiple commands to be run in sequence by calling rebar3 do <task1>,<task2>,...,<taskN>.
Command dependenciesRebar3 commands know their own dependencies. If a test run needs to fetch dependencies and build them, it will do so.
Command namespacesAllows multiple tools or commands to share the same name.
CompilingBuild the project, including fetching all of its dependencies by calling rebar3 compile
Clean up artifactsRemove the compiled beam files from a project with rebar3 clean or just remove the _builddirectory to remove all compilation artifacts
Code CoverageVarious commands can be instrumented to accumulate code coverage data (such as eunit or ct). Reports can be generated with rebar3 cover
Common TestThe test framework can be run by calling rebar3 ct
DependenciesRebar3 maintains local copies of dependencies on a per-project basis. They are fetched deterministically, can be locked, upgraded, fetched from source, packages, or from local directories. See Dependencies on the documentation website. Call rebar3 tree to show the whole dependency tree.
DocumentationPrint help for rebar3 itself (rebar3 help) or for a specific task (rebar3 help <task>). Full reference at
DialyzerRun the Dialyzer analyzer on the project with rebar3 dialyzer. Base PLTs for each version of the language will be cached and reused for faster analysis
EdocGenerate documentation using edoc with rebar3 edoc
Escript generationRebar3 can be used to generate escripts providing an easy way to run all your applications on a system where Erlang is installed
EunitThe test framework can be run by calling rebar3 eunit
Locked dependenciesDependencies are going to be automatically locked to ensure repeatable builds. Versions can be changed with rebar3 upgrade or rebar3 upgrade <app>, or locks can be released altogether with rebar3 unlock.
PackagesHex packages can be listed with rebar3 pkgs. They can be used as dependencies, will be cached locally for faster usage, and a local index will be used and updated with rebar3 update.
PathWhile paths are managed automatically, you can print paths to the current build directories with rebar3 path.
PluginsRebar3 can be fully extended with plugins. List or upgrade plugins by using the plugin namespace (rebar3 plugins).
ProfilesRebar3 can have subconfiguration options for different profiles, such as test or prod. These allow specific dependencies or compile options to be used in specific contexts. See Profiles in the docs.
ReleasesRebar3 supports building releases with the relx tool, providing a way to ship fully self-contained Erlang systems. Release update scripts for live code updates can also be generated.
ShellA full shell with your applications available can be started with rebar3 shell. From there, call tasks as r3:do(compile) to automatically recompile and reload the code without interruption
TarballsReleases can be packaged into tarballs ready to be deployed.
TemplatesConfigurable templates ship out of the box (try rebar3 new for a list or rebar3 new help <template> for a specific one). Custom templates are also supported, and plugins can also add their own.
Unstable namespaceWe use a namespace to provide commands that are still in flux, allowing to test more experimental features we are working on. See rebar3 unstable.
XrefRun cross reference analysis on the project with xref by calling rebar3 xref.

Migrating From rebar2

The grievances we had with Rebar 2.x were not fixable without breaking compatibility in some very important ways.
A full guide titled From Rebar 2.x to Rebar3 is provided on the documentation website.
Notable modifications include mandating a more standard set of directory structures, changing the handling of dependencies, moving some compilers (such as C, Diameter, ErlyDTL, or ProtoBuffs) to plugins rather than maintaining them in core rebar, and moving release builds from reltool to relx.

Additional Resources

In case of problems that cannot be solved through documentation or examples, you may want to try to contact members of the community for help. The community is also where you want to go for questions about how to extend rebar, fill in bug reports, and so on.
The main place to go for questions is the rebar mailing list. If you need quick feedback, you can try the #rebar channel Be sure to check the documentation first, just to be sure you're not asking about things with well known answers.
For bug reports, roadmaps, and issues, visit the github issues page.
General rebar community resources and links: