View Source Mix (Mix v1.17.2)
Mix is a build tool that provides tasks for creating, compiling, and testing Elixir projects, managing its dependencies, and more.
Mix.Project
The foundation of Mix is a project. A project can be defined by using
Mix.Project
in a module, usually placed in a file named mix.exs
:
defmodule MyApp.MixProject do
use Mix.Project
def project do
[
app: :my_app,
version: "1.0.0"
]
end
end
See the Mix.Project
module for detailed documentation on Mix projects.
Once the project is defined, a number of default Mix tasks can be run directly from the command line:
mix compile
- compiles the current projectmix test
- runs tests for the given projectmix run
- runs a particular command inside the project
Each task has its own options and sometimes specific configuration
to be defined in the project/0
function. You can use mix help
to list all available tasks and mix help NAME
to show help for
a particular task.
The best way to get started with your first project is by calling
mix new my_project
from the command line.
Mix.Task
Tasks are what make Mix extensible.
Projects can extend Mix behaviour by adding their own tasks. For example, adding the task below inside your project will make it available to everyone that uses your project:
defmodule Mix.Tasks.Hello do
use Mix.Task
def run(_) do
Mix.shell().info("Hello world")
end
end
The task can now be invoked with mix hello
.
See the Mix.Task
behaviour for detailed documentation on Mix tasks.
Dependencies
Mix also manages your dependencies and integrates nicely with the Hex package manager.
In order to use dependencies, you need to add a :deps
key
to your project configuration. We often extract the list of dependencies
into its own function:
defmodule MyApp.MixProject do
use Mix.Project
def project do
[
app: :my_app,
version: "1.0.0",
deps: deps()
]
end
defp deps do
[
{:ecto, "~> 2.0"},
{:plug, github: "elixir-lang/plug"}
]
end
end
You can run mix help deps
to learn more about dependencies in Mix.
Environments
Mix supports different environments. Environments allow developers to prepare and organize their project specifically for different scenarios. By default, Mix provides three environments:
:dev
- the default environment:test
- the environmentmix test
runs on:prod
- the environment your dependencies run on
The environment can be changed via the command line by setting
the MIX_ENV
environment variable, for example:
$ MIX_ENV=prod mix run server.exs
You can also specify that certain dependencies are available only for certain environments:
{:some_test_dependency, "~> 1.0", only: :test}
When running Mix via the command line, you can configure the default
environment or the preferred environment per task via the def cli
function in your mix.exs
. For example:
def cli do
[
default_env: :local,
preferred_envs: [docs: :docs]
]
end
The environment can be read via Mix.env/0
.
Targets
Besides environments, Mix supports targets. Targets are useful when a
project needs to compile to different architectures and some of the
dependencies are only available to some of them. By default, the target
is :host
but it can be set via the MIX_TARGET
environment variable.
When running Mix via the command line, you can configure the default
target or the preferred target per task via the def cli
function
in your mix.exs
. For example:
def cli do
[
default_target: :local,
preferred_targets: [docs: :docs]
]
end
The target can be read via Mix.target/0
.
Configuration
Mix allows you to configure the application environment of your application
and of your dependencies. See the Application
module to learn more about
the application environment. On this section, we will focus on how to configure
it at two distinct moments: build-time and runtime.
Avoiding the application environment
The application environment is discouraged for libraries. See Elixir's Library Guidelines for more information.
Build-time configuration
Whenever you invoke a mix
command, Mix loads the configuration
in config/config.exs
, if said file exists. It is common for the
config/config.exs
file itself to import other configuration based
on the current MIX_ENV
, such as config/dev.exs
, config/test.exs
,
and config/prod.exs
, by calling Config.import_config/1
:
import Config
import_config "#{config_env()}.exs"
We say config/config.exs
and all imported files are build-time
configuration as they are evaluated whenever you compile your code.
In other words, if your configuration does something like:
import Config
config :my_app, :secret_key, System.fetch_env!("MY_APP_SECRET_KEY")
The :secret_key
key under :my_app
will be computed on the host
machine before your code compiles. This can be an issue if the machine
compiling your code does not have access to all environment variables
used to run your code, as loading the config above will fail due to the
missing environment variable. Furthermore, even if the environment variable
is set, changing the environment variable will require a full recompilation
of your application by calling mix compile --force
(otherwise your project
won't start). Luckily, Mix also provides runtime configuration, which is
preferred in such cases and we will see next.
Runtime configuration
To enable runtime configuration in your release, all you need to do is
to create a file named config/runtime.exs
:
import Config
config :my_app, :secret_key, System.fetch_env!("MY_APP_SECRET_KEY")
This file is executed whenever your project runs. If you assemble
a release with mix release
, it also executes every time your release
starts.
Aliases
Aliases are shortcuts or tasks specific to the current project.
In the Mix.Task section, we have defined a task that would be available to everyone using our project as a dependency. What if we wanted the task to only be available for our project? Just define an alias:
defmodule MyApp.MixProject do
use Mix.Project
def project do
[
app: :my_app,
version: "1.0.0",
aliases: aliases()
]
end
defp aliases do
[
c: "compile",
hello: &hello/1,
paid_task: &paid_task/1
]
end
defp hello(_) do
Mix.shell().info("Hello world")
end
defp paid_task(_) do
Mix.Task.run("paid.task", [
"first_arg",
"second_arg",
"--license-key",
System.fetch_env!("SOME_LICENSE_KEY")
])
end
end
In the example above, we have defined three aliases. One is mix c
which is a shortcut for mix compile
. Another is named
mix hello
and the third is named mix paid_task
, which executes
the code inside a custom function to invoke the paid.task
task
with several arguments, including one pulled from an environment
variable.
Aliases may also be lists, specifying multiple tasks to be run consecutively:
[all: [&hello/1, "deps.get --only #{Mix.env()}", "compile"]]
In the example above, we have defined an alias named mix all
,
that prints "Hello world", then fetches dependencies specific
to the current environment, and compiles the project.
Aliases can also be used to augment existing tasks. Let's suppose
you want to augment mix clean
to clean another directory Mix does
not know about:
[clean: ["clean", &clean_extra/1]]
Where &clean_extra/1
would be a function in your mix.exs
with extra cleanup logic.
If the alias is overriding an existing task, the arguments given to the alias will be forwarded to the original task in order to preserve semantics. Otherwise arguments given to the alias are appended to the arguments of the last task in the list.
Another use case of aliases is to run Elixir scripts and shell commands, for example:
# priv/hello1.exs
IO.puts("Hello One")
# priv/hello2.exs
IO.puts("Hello Two")
# priv/world.sh
#!/bin/sh
echo "world!"
# mix.exs
defp aliases do
[
some_alias: ["hex.info", "run priv/hello1.exs", "cmd priv/world.sh"]
]
end
In the example above we have created the alias some_alias
that will
run the task mix hex.info
, then mix run
to run an Elixir script,
then mix cmd
to execute a command line shell script. This shows how
powerful aliases mixed with Mix tasks can be.
One common pitfall of aliases comes when trying to invoke the same task
multiple times. Mix tasks are designed to run only once. This prevents
the same task from being executed multiple times. For example, if there
are several tasks depending on mix compile
, the code will be compiled
only once.
Similarly, mix format
can only be invoked once. So if you have an alias
that attempts to invoke mix format
multiple times, it won't work unless
it is explicitly reenabled using Mix.Task.reenable/1
:
another_alias: [
"format --check-formatted priv/hello1.exs",
"cmd priv/world.sh",
fn _ -> Mix.Task.reenable("format") end,
"format --check-formatted priv/hello2.exs"
]
Some tasks are automatically reenabled though, as they are expected to
be invoked multiple times, such as: mix cmd
, mix do
, mix xref
, etc.
Finally, aliases defined in the current project do not affect its dependencies and aliases defined in dependencies are not accessible from the current project, with the exception of umbrella projects. Umbrella projects will run the aliases of its children when the umbrella project itself does not define said alias and there is no task with said name.
Environment variables
Several environment variables can be used to modify Mix's behavior.
Mix responds to the following variables:
MIX_ARCHIVES
- specifies the directory into which the archives should be installed (default:~/.mix/archives
)MIX_BUILD_PATH
- sets the projectMix.Project.build_path/0
config. This option must always point to a subdirectory inside a temporary directory. For instance, never "/tmp" or "_build" but "_build/PROD" or "/tmp/PROD", as required by Mix. This environment variable is used mostly by external build tools. For your CI servers, you likely want to useMIX_BUILD_ROOT
below.MIX_BUILD_ROOT
- sets the root directory where build artifacts should be written to. For example, "_build". IfMIX_BUILD_PATH
is set, this option is ignored.MIX_DEBUG
- outputs debug information about each task before running itMIX_DEPS_PATH
- sets the projectMix.Project.deps_path/0
config for the current project (default:deps
)MIX_ENV
- specifies which environment should be used. See EnvironmentsMIX_EXS
- changes the full path to themix.exs
fileMIX_HOME
- path to Mix's home directory, stores configuration files and scripts used by Mix (default:~/.mix
)MIX_INSTALL_DIR
(since v1.12.0) - specifies directory whereMix.install/2
keeps install cacheMIX_PATH
- appends extra code pathsMIX_PROFILE
- a list of comma-separated Mix tasks to profile the time spent on functions by the process running the taskMIX_QUIET
- does not print information messages to the terminalMIX_REBAR3
- path to rebar3 command that overrides the one Mix installs (default:~/.mix/rebar3
)MIX_TARGET
- specifies which target should be used. See TargetsMIX_XDG
- asks Mix to follow the XDG Directory Specification for its home directory and configuration files. This behavior needs to be opt-in due to backwards compatibility.MIX_HOME
has higher preference thanMIX_XDG
. If none of the variables are set, the default directory~/.mix
will be used
Environment variables that are not meant to hold a value (and act basically as
flags) should be set to either 1
or true
, for example:
$ MIX_DEBUG=1 mix compile
In addition, Mix also uses the following environment variables defined by other libraries
HEX_CACERTS_PATH
- use specified CA certificate file instead of default system CA certificates. This configures how HTTPS calls are made via Erlangssl
module to fetch remote archives and packages. For more details, seemix hex.config
.
Summary
Functions
Returns the default compilers used by Mix.
Sets Mix debug mode.
Returns true
if Mix is in debug mode, false
otherwise.
Ensures the given application from Erlang/OTP or Elixir and its dependencies are available in the path.
Returns the current Mix environment.
Changes the current Mix environment to env
.
Installs and starts dependencies.
Returns the directory where the current Mix.install/2
project
resides.
Returns whether Mix.install/2
was called in the current node.
The path for local archives or escripts.
Raises a Mix error that is nicely formatted, defaulting to exit status 1
.
Raises a Mix error that is nicely formatted.
Returns the current shell.
Sets the current shell.
Returns the Mix target.
Changes the current Mix target to target
.
Functions
@spec compilers() :: [atom()]
Returns the default compilers used by Mix.
It can be used in your mix.exs
to prepend or
append new compilers to Mix:
def project do
[compilers: Mix.compilers() ++ [:foo, :bar]]
end
@spec debug(boolean()) :: :ok
Sets Mix debug mode.
@spec debug?() :: boolean()
Returns true
if Mix is in debug mode, false
otherwise.
Ensures the given application from Erlang/OTP or Elixir and its dependencies are available in the path.
Generally speaking, you should list the Erlang application dependencies under
the :extra_applications
section of your mix.exs
. This must only be used by
Mix tasks which wish to avoid depending on Erlang/Elixir for certain reasons.
This function does not start the given applications.
@spec env() :: atom()
Returns the current Mix environment.
This function should not be used at runtime in application code (as opposed to infrastructure and build code like Mix tasks). Mix is a build tool and may not be available after the code is compiled (for example in a release).
To differentiate the program behavior depending on the environment, it is
recommended to use application environment through Application.get_env/3
.
Proper configuration can be set in config files, often per-environment
(see the Config
module for more information).
@spec env(atom()) :: :ok
Changes the current Mix environment to env
.
Be careful when invoking this function as any project configuration won't be reloaded.
This function should not be used at runtime in application code
(see env/0
for more information).
Installs and starts dependencies.
The given deps
should be in the same format as defined in a regular Mix
project. See mix help deps
for more information. As a shortcut, an atom
can be given as dependency to mean the latest version. In other words,
specifying :decimal
is the same as {:decimal, ">= 0.0.0"}
.
After each successful installation, a given set of dependencies is cached
so starting another VM and calling Mix.install/2
with the same dependencies
will avoid unnecessary downloads and compilations. The location of the cache
directory can be controlled using the MIX_INSTALL_DIR
environment variable.
This function can only be called outside of a Mix project and only with the same dependencies in the given VM.
Options
:force
- iftrue
, runs with empty install cache. This is useful when you want to update your dependencies or your install got into an inconsistent state. To use this option, you can also set theMIX_INSTALL_FORCE
environment variable. (Default:false
):verbose
- iftrue
, prints additional debugging information (Default:false
):consolidate_protocols
- iftrue
, runs protocol consolidation via themix compile.protocols
task (Default:true
):elixir
- if set, ensures the current Elixir version matches the given version requirement (Default:nil
):system_env
(since v1.13.0) - a list or a map of system environment variable names with respective values as binaries. The system environment is made part of theMix.install/2
cache, so different configurations will lead to different apps:config
(since v1.13.0) - a keyword list of keyword lists of compile-time configuration. The configuration is part of theMix.install/2
cache, so different configurations will lead to different apps. For this reason, you want to minimize the amount of configuration set through this option. UseApplication.put_all_env/2
for setting other runtime configuration.:config_path
(since v1.14.0) - path to a configuration file. If aruntime.exs
file exists in the same directory as the given path, it is loaded too.:lockfile
(since v1.14.0) - path to a lockfile to be used as a basis of dependency resolution.:start_applications
(since v1.15.3) - iftrue
, ensures that installed app and its dependencies are started after install (Default:true
)
Examples
Installing :decimal
and :jason
:
Mix.install([
:decimal,
{:jason, "~> 1.0"}
])
Installing :nx
and :exla
, and configuring the underlying applications
and environment variables:
Mix.install(
[:nx, :exla],
config: [
nx: [default_backend: EXLA]
],
system_env: [
XLA_TARGET: "cuda111"
]
)
Installing a Mix project as a path dependency along with its configuration and deps:
# $ git clone https://github.com/hexpm/hexpm /tmp/hexpm
# $ cd /tmp/hexpm && mix setup
Mix.install(
[
{:hexpm, path: "/tmp/hexpm", env: :dev},
],
config_path: "/tmp/hexpm/config/config.exs",
lockfile: "/tmp/hexpm/mix.lock"
)
Hexpm.Repo.query!("SELECT COUNT(1) from packages")
#=> ...
The example above can be simplified by passing the application
name as an atom for :config_path
and :lockfile
:
Mix.install(
[
{:hexpm, path: "/tmp/hexpm", env: :dev},
],
config_path: :hexpm,
lockfile: :hexpm
)
Limitations
There is one limitation to Mix.install/2
, which is actually an Elixir
behavior. If you are installing a dependency that defines a struct or
macro, you cannot use the struct or macro immediately after the install
call. For example, this won't work:
Mix.install([:decimal])
%Decimal{} = Decimal.new(42)
That's because Elixir first expands all structs and all macros, and then
it executes the code. This means that, by the time Elixir tries to expand
the %Decimal{}
struct, the dependency has not been installed yet.
Luckily this has a straightforward solution, which is to move the code inside a module:
Mix.install([:decimal])
defmodule Script do
def run do
%Decimal{} = Decimal.new(42)
end
end
Script.run()
The contents inside defmodule
will only be expanded and executed
after Mix.install/2
runs, which means that any struct, macros,
and imports will be correctly handled.
Environment variables
The MIX_INSTALL_DIR
environment variable configures the directory that
caches all Mix.install/2
. It defaults to the "mix/install" folder in the
default user cache of your operating system. You can use install_project_dir/0
to access the directory of an existing install (alongside other installs):
iex> Mix.install([])
iex> Mix.install_project_dir()
The MIX_INSTALL_FORCE
is available since Elixir v1.13.0 and forces
Mix.install/2
to discard any previously cached entry of the current install.
The MIX_INSTALL_RESTORE_PROJECT_DIR
environment variable may be specified
since Elixir v1.16.2. It should point to a previous installation directory,
which can be obtained with Mix.install_project_dir/0
(after calling Mix.install/2
).
Using a restore dir may speed up the installation, since matching dependencies
do not need be refetched nor recompiled. This environment variable is ignored
if :force
is enabled.
@spec install_project_dir() :: Path.t() | nil
Returns the directory where the current Mix.install/2
project
resides.
@spec installed?() :: boolean()
Returns whether Mix.install/2
was called in the current node.
@spec path_for(:archives | :escripts) :: String.t()
The path for local archives or escripts.
Raises a Mix error that is nicely formatted, defaulting to exit status 1
.
@spec raise(binary(), [{:exit_status, non_neg_integer()}]) :: no_return()
Raises a Mix error that is nicely formatted.
Options
:exit_status
- defines exit status, defaults to1
@spec shell() :: module()
Returns the current shell.
shell/0
can be used as a wrapper for the current shell. It contains
conveniences for requesting information from the user, printing to the
shell and so forth. The Mix shell is swappable (see shell/1
), allowing
developers to use a test shell that simply sends messages to the current
process instead of performing IO (see Mix.Shell.Process
).
By default, this returns Mix.Shell.IO
.
Examples
Mix.shell().info("Preparing to do something dangerous...")
if Mix.shell().yes?("Are you sure?") do
# do something dangerous
end
@spec shell(module()) :: :ok
Sets the current shell.
As an argument you may pass Mix.Shell.IO
, Mix.Shell.Process
,
Mix.Shell.Quiet
, or any module that implements the Mix.Shell
behaviour.
After calling this function, shell
becomes the shell that is
returned by shell/0
.
Examples
iex> Mix.shell(Mix.Shell.IO)
:ok
You can use shell/0
and shell/1
to temporarily switch shells,
for example, if you want to run a Mix Task that normally produces
a lot of output:
shell = Mix.shell()
Mix.shell(Mix.Shell.Quiet)
try do
Mix.Task.run("noisy.task")
after
Mix.shell(shell)
end
@spec target() :: atom()
Returns the Mix target.
@spec target(atom()) :: :ok
Changes the current Mix target to target
.
Be careful when invoking this function as any project configuration won't be reloaded.