# `Mix.Shell.Process`
[🔗](https://github.com/elixir-lang/elixir/blob/7ff272706afc522e74121493b7166719985cb099/lib/mix/lib/mix/shell/process.ex#L5)

Mix shell that uses the current process mailbox for communication.

This module provides a Mix shell implementation that uses
the current process mailbox for communication instead of IO.

As an example, when `Mix.shell().info("hello")` is called,
the following message will be sent to the calling process:

    {:mix_shell, :info, ["hello"]}

This is mainly useful in tests, allowing us to assert
if given messages were received or not instead of performing
checks on some captured IO. There is also a `flush/1` function
responsible for flushing all `:mix_shell` related messages
from the process inbox.

## Examples

The first step is to set the Mix shell to this module:

    Mix.shell(Mix.Shell.Process)

Then if your Mix task calls:

    Mix.shell().info("hello")

You should be able to receive it in your tests as long as
they run in the same process:

    assert_receive {:mix_shell, :info, [msg]}
    assert msg == "hello"

You can respond to prompts in tests as well:

    send(self(), {:mix_shell_input, :prompt, "Pretty cool"})
    Mix.shell().prompt("How cool was that?!")
    #=> "Pretty cool"

# `cmd`

Executes the given command and forwards its messages to
the current process.

# `error`

Forwards the error to the current process.

# `flush`

Flushes all `:mix_shell` and `:mix_shell_input` messages from the current process.

If a callback is given, it is invoked for each received message.

## Examples

    flush(&IO.inspect/1)

# `info`

Forwards the message to the current process.

# `print_app`

Prints the current application if it
was not printed yet.

# `prompt`

Forwards the message to the current process.

It also checks the inbox for an input message matching:

    {:mix_shell_input, :prompt, value}

If one does not exist, it will abort since there was no shell
process inputs given. `value` must be a string.

## Examples

The following will answer with `"Meg"` to the prompt
`"What's your name?"`:

    # The response is sent before calling prompt/1 so that prompt/1 can read it
    send(self(), {:mix_shell_input, :prompt, "Meg"})
    Mix.shell().prompt("What's your name?")

# `yes?`

Forwards the message to the current process.

It also checks the inbox for an input message matching:

    {:mix_shell_input, :yes?, value}

If one does not exist, it will abort since there was no shell
process inputs given. `value` must be `true` or `false`.

## Example

    # Send the response to self() first so that yes?/2 will be able to read it
    send(self(), {:mix_shell_input, :yes?, true})
    Mix.shell().yes?("Are you sure you want to continue?")

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*Consult [api-reference.md](api-reference.md) for complete listing*