#
View Source Mix.Task behaviour (Mix v1.15.7)

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

A Mix task can be defined by `use 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"]

> #### `use Mix.Task`

> When you `use Mix.Task`, the `Mix.Task` module will set `@behaviour Mix.Task` and define default values for the module attributes documented in the section below.

## Module attributes

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"]

A task will typically depend on one of the following tasks:

- "loadpaths" - this ensures dependencies are available and compiled. If you are publishing a task as part of a library to be used by others, and your task does not need to interact with the user code in any way, this is the recommended requirement

- "app.config" - additionally compiles and loads the runtime configuration for the current project. If you are creating a task to be used within your application or as part of a library, which must invoke or interact with the user code, this is the minimum recommended requirement

- "app.start" - additionally starts the supervision tree of the current project and its dependencies

Finally, set `@recursive true` if you want the task to run on each umbrella child in an umbrella project.

## 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.

# Summary

## Types

task_module()
task_name()

## Callbacks

run(command_line_args)

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

## Functions

alias?(task)

Checks if the given `task` name is an alias.

all_modules()

Returns all loaded task modules.

clear()

Clears all invoked tasks, allowing them to be reinvoked.

get(task)

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

get!(task)

Receives a task name and retrieves the corresponding task module.

load_all()

Loads all tasks in all code paths.

load_tasks(dirs)

Loads all tasks in the given `paths`.

moduledoc(module)

Gets the moduledoc for the given task `module`.

preferred_cli_env(task) deprecated

See `Mix.CLI.preferred_cli_env/1`.

recursing?()

Indicates if the current task is recursing.

recursive(module)

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

reenable(task)

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

requirements(module)

Gets the list of requirements for the given task.

rerun(task, args \\ [])

Reruns `task` with the given arguments.

run(task, args \\ [])

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

run_in_apps(task, apps, args \\ [])

Runs recursive tasks in the specified list of children apps for umbrella projects.

shortdoc(module)

Gets the shortdoc for the given task `module`.

task?(module)

Returns `true` if given module is a task.

task_name(module)

Returns the task name for the given `module`.

# Types

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# task_module()

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    @type task_module() :: atom()

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# task_name()

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

# Callbacks

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# run(command_line_args)

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

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

# Functions

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# alias?(task)

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    @spec 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`.

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# all_modules()

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    @spec 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.

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# clear()

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    @spec clear() :: :ok

Clears all invoked tasks, allowing them to be reinvoked.

This operation is not recursive.

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# get(task)

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    @spec 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`.

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# get!(task)

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    @spec get!(task_name()) :: task_module()

Receives a task name and retrieves the corresponding task module.

## Exceptions

- `Mix.NoTaskError` - raised if the task could not be found
- `Mix.InvalidTaskError` - raised if the task is not a valid `Mix.Task`

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# load_all()

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    @spec load_all() :: [task_module()]

Loads all tasks in all code paths.

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# load_tasks(dirs)

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

Loads all tasks in the given `paths`.

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# moduledoc(module)

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

Gets the moduledoc for the given task `module`.

Returns the moduledoc or `nil`.

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# preferred_cli_env(task)

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This function is deprecated. Configure the environment in your mix.exs.

See `Mix.CLI.preferred_cli_env/1`.

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# recursing?()

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    @spec 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.

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# recursive(module)

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    @spec recursive(task_module()) :: boolean()

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

Returns `true` or `false`.

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# reenable(task)

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    @spec reenable(task_name()) :: :ok

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

Both alias and the regular stack are re-enabled when this function is called.

If an umbrella project reenables a task, it is re-enabled for all child projects.

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# requirements(module)

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    @spec 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.

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# rerun(task, args \\ [])

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    @spec 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.

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# run(task, args \\ [])

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    @spec 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.

## Examples

    iex> Mix.Task.run("format", ["mix.exs"])
    :ok

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# run_in_apps(task, apps, args \\ [])

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    @spec run_in_apps(task_name(), [atom()], [any()]) :: any()

Runs recursive tasks in the specified list of children apps for umbrella projects.

If the task is not recursive (whose purpose is to be run in children applications), it runs at the project root level as usual. Calling this function outside of an umbrella project root fails.

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# shortdoc(module)

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

Gets the shortdoc for the given task `module`.

Returns the shortdoc or `nil`.

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# task?(module)

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    @spec task?(task_module()) :: boolean()

Returns `true` if given module is a task.

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# task_name(module)

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    @spec task_name(task_module()) :: task_name()

Returns the task name for the given `module`.

## Examples

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