Erlang.mk can fetch and compile the dependencies that your project requires. Erlang.mk improves upon the concepts introduced by Rebar, so they should be familiar to many seasoned Erlang developers.
Erlang.mk is not a package manager, nor is it trying to be, but it does include an index of Erlang packages to make discovering useful projects easier.
This chapter will explain how to use packages, add dependencies to your project or bundle them directly in a single repository.
Erlang.mk gives you access to nearly 500 packages, with more being added regularly.
To find a package, search for it:
$ make search q=pool
This will return all packages matching this word, like worker pool and acceptor pool projects.
You can also list everything and use regular command line tools to find what you need, for example:
$ make search | less
Once you find the package you need, adding it as a dependency to your project is a one-liner:
DEPS = cowboy
And that’s it! The next time you run
make, Erlang.mk will
fetch and compile Cowboy. Erlang.mk will also ensure Cowboy
is available whenever you use the shell, run tests and any
Note though that you may need to specify the version of a dependency to use. Otherwise, you may get an outdated version, since the package index used by Erlang.mk is not always updated with the latest version of each package.
DEPS = cowboy dep_cowboy_commit = 2.8.0
Erlang.mk will fill in the application resource file with
all applications found in
DEPS. But not all dependencies
are Erlang applications, and not all dependencies need to
be a runtime dependency. That’s where the
variable comes in: it works just like
DEPS, except the
dependencies listed there will not be added as runtime
For example, you could add a parse transform project like this to make it available only at build time:
BUILD_DEPS = erlando
Or you could depend on a C project directly, if you are building a NIF:
BUILD_DEPS = leveldb dep_leveldb = git https://github.com/basho/leveldb 2.1.3
This dependency will be built before your application, so you could easily copy the resulting shared file into your priv/ directory as part of the build process. More information about that in the NIFs and port drivers chapter.
LOCAL_DEPS, allows specifying runtime
dependencies which are part of Erlang/OTP itself, but also
dependencies that are included in the repository. Since they
are already on your system, there is no need to fetch them.
Do note that there is no way to choose the version, the
application used will be the one already on your system.
You could depend on the Crypto application, for example:
LOCAL_DEPS = crypto
Erlang.mk comes with additional types of dependencies.
TEST_DEPS for dependencies used only for testing:
TEST_DEPS = ct_helper dep_ct_helper = git https://github.com/ninenines/ct_helper master
DOC_DEPS for dependencies used only when building documentation:
DOC_DEPS = edown
REL_DEPS for dependencies required to build the release,
or to include extra applications in the release:
REL_DEPS = recon
SHELL_DEPS for dependencies to make available when running
make shell command:
SHELL_DEPS = tddreloader
All these will be documented in more details in their respective chapters.
Note that these additional types of dependencies will only
be fetched after normal dependencies by default. You can
force a dependency to be downloaded first by extending the
deps:: before including erlang.mk, for example:
Sometimes dependencies are allowed to be missing. However, your application
may depend on an optional application being started. To ensure that an
optional dependency is started before your application, the variable
OPTIONAL_DEPS may be used:
OPTIONAL_DEPS = quicer
The top-level project can then decide whether to include this
application by adding it to its
BUILD_DEPS and including
it in the release dependencies.
By default, Erlang.mk will look into its package index to find the project you are looking for, if you only provide its name. This is this case:
DEPS = cowboy
If you need a different version, you need to define another variable. There are two ways to do this, each being useful for different reasons.
If you simply want to change the commit number, all you
need to do is to define the
variable. In the case of Cowboy, this would look like this:
DEPS = cowboy dep_cowboy_commit = 2.0.0-pre.2
Erlang.mk will use the package index to get all information about Cowboy, except the commit number which will be overridden.
If you need to set the fetch method or repository information
too, for example because you want to use your own fork, or
simply because the project is missing from the index, you
can define the
dep_$(DEP_NAME) variable with everything:
DEPS = cowboy dep_cowboy = git https://github.com/essen/cowboy 2.0.0-pre.2
This will fetch Cowboy from your fork at the given commit.
Erlang.mk comes with a number of different fetch methods. You can fetch from Git, Mercurial, SVN, to name a few. There are fetch methods that will work everywhere, and fetch methods that will only work in a given environment.
The following table lists all existing methods:
git repo commit
Clone the Git repository and checkout the given version
git repo commit subfolder
Clone the Git repository, checkout the given version and use one of its subfolders as a dependency
Initialize and update the Git submodule
hg repo commit
Clone the Mercurial repository and update to the given version
Checkout the given SVN repository
Recursively copy a local directory
Symbolically link a local directory
hex version [pkg]
Download the given project version from hex.pm
Always fail, reserved for internal use
Legacy Erlang.mk fetcher, reserved for internal use
hg methods both have a repository and commit.
You can use any valid commit, tag or branch in that repository
for the commit value.
For example, to fetch Cowboy with tag 2.0.0-pre.2 from Git:
dep_cowboy = git https://github.com/ninenines/cowboy 2.0.0-pre.2
Or to fetch Ehsa tag 4.0.3 from Mercurial:
dep_ehsa = hg https://bitbucket.org/a12n/ehsa 4.0.3
Git also comes with a concept of submodules. Erlang.mk can
automatically initializes and updates submodules for dependencies,
as long as they were added beforehand using
git submodule add:
dep_cowboy = git-submodule
svn method only has a repository value, but that’s
simply because the SVN repository URL can also contain
the path and commit.
This would fetch an example project from the trunk:
dep_ex1 = svn https://example.com/svn/trunk/project/ex1
And this would fetch a separate example project from a specific commit:
dep_ex2 = svn svn://example.com/svn/branches/erlang-proj/ex2@264
You can copy a directory from your machine using the
It only takes the path to copy from:
dep_cowboy = cp $(HOME)/ninenines/cowboy
Finally, you can use a package from the Hex repository:
dep_cowboy = hex 1.0.3
If the package on Hex has a different name than the application, you can provide it after the version:
dep_uuid = hex 1.7.5 uuid_erl
If none of the existing methods fit your use, you can simply
define your own. Erlang.mk will consider all variables that
are named as
dep_fetch_$(METHOD) to be available fetch
methods. You can do anything inside this variable, as long
as you create a folder named $(DEPS_DIR)/$(call dep_name,$1).
Or in layman terms, if your dependency is Cowboy, this would
To give an example, this is what the Git method does:
define dep_fetch_git git clone -q -n -- $(call dep_repo,$1) $(DEPS_DIR)/$(call dep_name,$1); \ cd $(DEPS_DIR)/$(call dep_name,$1) && git checkout -q $(call dep_commit,$1); endef
Note that, like dependency information, this custom fetch method must be written before including erlang.mk.
The order in which dependencies are fetched and built is well defined. This means that Erlang.mk will get the same applications regardless of the command or options being used.
In tree traversal terms, where the list of dependencies is a tree, Erlang.mk fetches everything using the pre-order traversal method. The steps can be summarized like this, starting from the root application:
- Fetch all dependencies for the application
- Build first dependency
- Build Nth dependency
- Build last dependency
Every time a dependency is built, these same steps are followed, recursively.
Do note that the first step, fetching all dependencies of an application, is not guaranteed to be ordered. The reason for this is that it is not possible to have the same dependency listed twice in a single application, and therefore there can be no conflicts. Remember, this step only fetches, at no point are different applications built in parallel.
What about conflicts between the dependencies of different applications? Simple. Since builds are ordered, this means that the first version of an application that is fetched will be the one that wins.
This means that if project A depends on projects B and C, in this order, and that both B and C depend on a different version of D, it will always be B’s version of D that wins, because we fetch the dependencies of B before fetching those from C.
Similarly, if project A depends on projects B, C and D, regardless of the order, and A, B and C depend on a different version of D, it will always be A’s version that wins, because we fetch all dependencies of A before fetching those from B or C.
Once a dependency is built, it will not be built again by default. Typically dependencies do not need to be recompiled and this speeds up building immensely. There are a few ways to force recompiling a dependency however:
- The dependency directory is a symbolic link; the dependency will always be recompiled.
The dependency is built directly, for example with a command
make -C deps/cowlib, or
makein the dependency’s directory.
FULLis set, for example
make FULL=1. This will force building of all dependencies. This can be added to your Makefile before including erlang.mk.
ebin/dep_builtin the dependency is removed.
You can fetch all dependencies recursively without building anything,
make fetch-deps command. It follows the same rules described
in the section above.
You can list all dependencies recursively, again without building
anything, with the
make list-deps command. It will obviously need
to fetch all dependencies exactly like
make fetch-deps. Once
everything is fetched, it prints a sorted list of absolute paths to the
list-deps work on the
DEPS lists only. To also fetch/list
SHELL_DEPS, you have two possibilities:
You can use
make fetch-shell-depscommands respectively. If you want to list them, you can use
You can use
make list-depswith the Makefile variable
DEP_TYPESset to a list of dependency types you want. The types are
shellrespectively. For example, you can list test and doc dependencies with
make list-deps DEP_TYPES='test doc'.
Note that only first level ‘TEST_DEPS
SHELL_DEPS are included, not dependencies’ one. In other word,
make list-test-deps lists the
TEST_DEPS of your project, but not
TEST_DEPS of the projects yours depend on.
No matter which method you use,
DEPS are always
make fetch-* commands store the complete list of
dependencies in files named
$(ERLANG_MK_RECURSIVE_SHELL_DEPS_LIST). Those files are simply printed
make list-* commands.
make list-* commands are made for human beings. If you need the list
of dependencies in a Makefile or a script, you should use the content
of those files directly instead. The reason is that
make fetch-* and
make list-* may have unwanted content in their output, such as actual
fetching of dependencies.
You can obtain information about all dependencies with
make query-deps family of commands:
make query-depswill list dependencies found in
make query-doc-depswill list documentation dependencies of the current project.
make query-rel-depswill list release dependencies of the current project.
make query-shell-depswill list shell dependencies of the current project.
make query-test-depswill list test dependencies of the current project.
By default the information printed will be the dependency name,
fetch method, repository and version, prefixed by the current
project’s name. But this output can be customized via the
$ make query-deps QUERY="name fetch_method repo version extra absolute_path"
The following options are available:
- The dependency name.
- The dependency’s fetch method.
- The dependency’s repository.
- The dependency’s version, tag or commit.
- Any additional information specific to the fetch method used.
- The dependency’s location after it has been fetched.
Fields that have no value will print
-. For example
not all fetch methods have a value for the
The value for
extra, when available, will be formatted
with the name of the information printed prefixed. For
example the hex fetch method will add
package-name=uuid_erl for the
Sometimes, you may want to ignore dependencies entirely. Not even fetch them. You may want to do this because a project you depend on depends on an application you do not need (like a dependency for building documentation or testing). Or maybe the dependency is already installed on your system.
To ignore a dependency, simply add it to the
IGNORE_DEPS += edown proper
This will only ignore dependencies that are needed for building. It is therefore safe to write:
IGNORE_DEPS += edown proper TEST_DEPS = proper
The PropEr application will be fetched as intended when
make tests or
make check. It will however
not be fetched when running
Dependencies are fetched in $(DEPS_DIR). By default this is the deps directory. You can change this default, but you should only do so if it was not defined previously. Erlang.mk uses this variable to tell dependencies where to fetch their own dependencies.
You will therefore need to use
?= instead of
=. Of course,
if you know you will never use this project as a dependency,
= will work. But to avoid it biting you later on, do this:
DEPS_DIR ?= $(CURDIR)/libs
$(CURDIR) part is important, otherwise dependencies of
dependencies will be fetched in the wrong directory.
Erlang.mk will also export the
REBAR_DEPS_DIR variable for
compatibility with Rebar build tools, as long as they are
In addition to the dependencies that are fetched, Erlang.mk also allows you to have dependencies local to your repository. This kind of layout is sometimes called multi-application repositories, or repositories with multiple applications.
They work exactly the same as remote dependencies, except:
- They are not fetched
- They are not autopatched
They are not deleted on
- They are not automatically added to the application resource file
To properly fill the application resource file and compile apps in
the right order, you will need to define the
for each relevant application, the same as for OTP applications. Apps
can depend on each other in this way, and their compilation order
will follow the same rules as regular dependencies in
LOCAL_DEPS variable, if defined, will determine which
apps (along with their dependencies) to build, and also which apps
should be added to the top-level application resource file, if there
is one. This may be useful, for example, for specifying a different
set of apps to build for different releases. If
LOCAL_DEPS is not
defined, then all apps in the $(APPS_DIR) will be built, but none
will be automatically added to the top-level application resource
If there is a conflict between a local dependency and a remote dependency, then the local dependency always wins; an error will be triggered when trying to fetch the conflicting remote dependency.
To start using dependencies local to the repository, simply create a folder named $(APPS_DIR). By default, this folder is the apps/ directory.
You can use Erlang.mk to bootstrap local dependencies by
using the command
make new-app or
make new-lib. This
command will create the necessary directories and bootstrap
For example, to create a full fledged OTP application as a local dependency:
$ make new-app in=webchat
Or, the same as an OTP library:
$ make new-lib in=webchat
Templates also work with local dependencies, from the root directory of the project. You do need however to tell Erlang.mk to create the files in the correct application:
$ make new t=gen_server n=my_server in=webchat
It’s possible to use Erlang.mk with only applications in $(APPS_DIR), and nothing at the root of the repository. Just create a folder, put the erlang.mk file in it, write a Makefile that includes it, and start creating your applications.
Similarly, it’s possible to have a repository with only dependencies found in $(DEPS_DIR). You just need to create a Makefile and specify the dependencies you want. This allows you to create a repository for handling the building of releases, for example.
Erlang.mk will automatically patch all the dependencies it fetches. It needs to do this to ensure that the dependencies become compatible with not only Erlang.mk, but also with the version of Erlang.mk that is currently used.
When fetching a dependency, the following operations are performed:
- Fetch the dependency using the configured fetch method
If it contains a configure.ac or configure.in file, run
autoreconf -Wall -vif -I m4
- If it contains a configure script, run it
- Run autopatch on the project
Autopatch first checks if there is any project-specific patch
enabled. There are currently two:
ELIXIR_PATCH for the
HUT_PATCH for the
Otherwise, autopatch performs different operations depending on the kind of project it finds the dependency to be.
- Rebar projects are automatically converted to use Erlang.mk as their build tool. This essentially patches Rebar out, and fixes and converts the project to be compatible with Erlang.mk.
- Erlang.mk projects have their Makefile patched, if necessary, to include the top-level project’s Erlang.mk. This is to ensure that functionality works across all dependencies, even if the dependency’s Erlang.mk is outdated. The patched Makefile can be safely committed if necessary.
- Other Erlang projects get a small Erlang.mk Makefile generated automatically.
- Projects with no source directory and no Makefile get an empty Makefile generated, for compatibility purposes.
- Other projects with no Makefile are left untouched.
You can add additional commands to be run immediately before
or after autopatch is done by extending the target
autopatch-$(dep)::, for example this would remove
autopatch-ranch:: rm -f $(DEPS_DIR)/ranch/src/ranch_proxy_header.erl
A common use case for this feature is to apply a PATCH file on the dependency immediately after fetching it. It can also be used to add compiler options, for example:
autopatch-couchbeam:: printf "\nERLC_OPTS += -DWITH_JIFFY\n" >> $(DEPS_DIR)/couchbeam/Makefile
The commands will run before autopatch when the target is defined before including erlang.mk, and after otherwise.
You can disable the replacing of the erlang.mk file by
NO_AUTOPATCH_ERLANG_MK = 1
You can also disable autopatch entirely for a few select
projects using the
NO_AUTOPATCH = cowboy ranch cowlib
When there are duplicate modules found in both applications and their dependencies, some tasks may fail. Erlang expects modules to be unique in general.
When the duplicates are found in dependencies, you will need to remove one of the duplicates at fetch time. To do so, you can add a rule similar to this to your Makefile before including erlang.mk:
DEPS_DIR = $(CURDIR)/deps deps:: $(DEPS_DIR)/cowlib $(verbose) rm -f $(DEPS_DIR)/cowlib/src/cow_ws.erl
This must be done from the application that has this dependency.
Only define the
DEPS_DIR variable if necessary.
It is possible to temporarily skip all dependency operations.
This is done by defining the
SKIP_DEPS variable. Use cases
include being somewhere with no connection to download them,
or perhaps a peculiar setup.
A typical usage would be:
$ make SKIP_DEPS=1
When the variable is defined:
- Dependencies will not be compiled or downloaded when required
The dependency directory $(DEPS_DIR) will not be removed on
This variable only applies to remote dependencies.