Mix.Task behaviour (Mix v1.13.0-dev) View Source

Provides conveniences for creating, loading, and manipulating Mix tasks.

A Mix task can be defined by using Mix.Task in a module whose name begins with Mix.Tasks. and which defines the run/1 function. Typically, task modules live inside the lib/mix/tasks/ directory, and their file names use dot separators instead of underscores (e.g. deps.clean.ex) - although ultimately the file name is not relevant.

For example:

# lib/mix/tasks/echo.ex
defmodule Mix.Tasks.Echo do
  @moduledoc "Printed when the user requests `mix help echo`"
  @shortdoc "Echoes arguments"

  use Mix.Task

  @impl Mix.Task
  def run(args) do
    Mix.shell().info(Enum.join(args, " "))
  end
end

The command name will correspond to the portion of the module name following Mix.Tasks.. For example, a module name of Mix.Tasks.Deps.Clean corresponds to a task name of deps.clean.

The run/1 function will receive a list of all command line arguments passed, according to the user's terminal.

For example, if the args in the above echo task were inspected, you might see something like this:

mix echo 'A and B' C --test
["A and B", "C", "--test"]

Define the @shortdoc attribute if you wish to make the task publicly visible on mix help. Omit this attribute if you do not want your task to be listed via mix help. The @moduledoc attribute may override @shortdoc. The task will not appear in mix help if documentation for the entire module is hidden with @moduledoc false.

If a task has requirements, they can be listed using the @requirements attribute. For example:

@requirements ["app.config"]

Tasks typically depend on the "app.config" task, when they need to access code from the current project with all apps already configured, or the "app.start" task, when they also need those apps to be already started:

@requirements ["app.start"]

You can also run tasks directly with run/2.

Attributes

There are a few attributes available in Mix tasks to configure them in Mix:

  • @shortdoc - makes the task public with a short description that appears on mix help
  • @recursive - runs the task recursively in umbrella projects
  • @requirements - list of required tasks to be run before the task
  • @preferred_cli_env - recommends an environment in which to run the task. It is used only if MIX_ENV is not yet set. Note @preferred_cli_env is not loaded from dependencies as we need to know the environment in order to load the dependencies themselves. In those cases, you can set the preferred_cli_env configuration under def project in your mix.exs

Documentation

Users can read the documentation for public Mix tasks by running mix help my_task. The documentation that will be shown is the @moduledoc of the task's module.

Link to this section Summary

Callbacks

A task needs to implement run which receives a list of command line args.

Functions

Checks if the given task name is an alias.

Returns all loaded task modules.

Clears all invoked tasks, allowing them to be reinvoked.

Receives a task name and returns the corresponding task module if one exists.

Receives a task name and retrieves the corresponding task module.

Loads all tasks in all code paths.

Loads all tasks in the given paths.

Gets the moduledoc for the given task module.

Gets preferred CLI environment for the task.

Indicates if the current task is recursing.

Checks if the task should be run recursively for all sub-apps in umbrella projects.

Reenables a given task so it can be executed again down the stack.

Gets the list of requirements for the given task.

Reruns task with the given arguments.

Conditionally runs the task (or alias) with the given args.

Gets the shortdoc for the given task module.

Returns true if given module is a task.

Returns the task name for the given module.

Link to this section Types

Specs

task_module() :: atom()

Specs

task_name() :: String.t() | atom()

Link to this section Callbacks

Specs

run(command_line_args :: [binary()]) :: any()

A task needs to implement run which receives a list of command line args.

Link to this section Functions

Specs

alias?(task_name()) :: boolean()

Checks if the given task name is an alias.

Returns false if the given name is not an alias or if it is not a task.

For more information about task aliasing, take a look at the "Aliases" section in the docs for Mix.

Specs

all_modules() :: [task_module()]

Returns all loaded task modules.

Modules that are not yet loaded won't show up. Check load_all/0 if you want to preload all tasks.

Specs

clear() :: :ok

Clears all invoked tasks, allowing them to be reinvoked.

This operation is not recursive.

Specs

get(task_name()) :: task_module() | nil

Receives a task name and returns the corresponding task module if one exists.

Returns nil if the module cannot be found, if it is an alias, or if it is not a valid Mix.Task.

Specs

get!(task_name()) :: task_module()

Receives a task name and retrieves the corresponding task module.

Exceptions

Specs

load_all() :: [task_module()]

Loads all tasks in all code paths.

Specs

load_tasks([List.Chars.t()]) :: [task_module()]

Loads all tasks in the given paths.

Specs

moduledoc(task_module()) :: String.t() | nil | false

Gets the moduledoc for the given task module.

Returns the moduledoc or nil.

Specs

preferred_cli_env(task_name()) :: atom() | nil

Gets preferred CLI environment for the task.

Returns environment (for example, :test, or :prod), or nil.

Link to this function

recursing?()

View Source (since 1.8.0)

Specs

recursing?() :: boolean()

Indicates if the current task is recursing.

This returns true if a task is marked as recursive and it is being executed inside an umbrella project.

Specs

recursive(task_module()) :: boolean()

Checks if the task should be run recursively for all sub-apps in umbrella projects.

Returns true or false.

Specs

reenable(task_name()) :: :ok

Reenables a given task so it can be executed again down the stack.

Both alias and the regular stack are reenabled when this function is called.

If an umbrella project reenables a task, it is reenabled for all child projects.

Link to this function

requirements(module)

View Source (since 1.11.0)

Specs

requirements(task_module()) :: []

Gets the list of requirements for the given task.

Returns a list of strings, where the string is expected to be a task optionally followed by its arguments.

Specs

rerun(task_name(), [any()]) :: any()

Reruns task with the given arguments.

This function reruns the given task; to do that, it first re-enables the task and then runs it as normal.

Specs

run(task_name(), [any()]) :: any()

Conditionally runs the task (or alias) with the given args.

If there exists a task matching the given task name and it has not yet been invoked, this will run the task with the given args and return the result.

If there is an alias defined for the given task name, the alias will be invoked instead of the original task.

If the task or alias has already been invoked, subsequent calls to run/2 will abort without executing and return :noop.

Remember: by default, tasks will only run once, even when called repeatedly! If you need to run a task multiple times, you need to re-enable it via reenable/1 or call it using rerun/2.

run/2 raises an exception if an alias or a task cannot be found or if the task is invalid. See get!/1 for more information.

Specs

shortdoc(task_module()) :: String.t() | nil

Gets the shortdoc for the given task module.

Returns the shortdoc or nil.

Specs

task?(task_module()) :: boolean()

Returns true if given module is a task.

Specs

task_name(task_module()) :: task_name()

Returns the task name for the given module.

Examples

iex> Mix.Task.task_name(Mix.Tasks.Test)
"test"