LoggerIexBackend

LoggerIexBackend is a Logger Backend for IEx interactive sessions.

If you have run into an IEx session of an Elixir application that makes exhaustive use of standard output logging, you probably have found a mostly unusable interactive shell. This is usually solved disabling logging, increasing logger lever or using an alternative backend like LoggerFileBackend.

LoggerIexBackend solves this problem and also enables logging debugging with tools like logs filtering and dynamic log configuration.

Example

Given the following code example:

defmodule Example do
  require Logger

  def foo() do
    Logger.debug("A foo message")
  end

  defmodule Bar do
    require Logger

    def bar() do
      Logger.info("A bar message")
    end
  end
end

We can use LoggerIexBackend in a interactive shell like this:

iex> Example.foo()
00:00:01.000 [debug] A foo message
:ok
iex> LoggerIexBackend.start()
{:ok, #PID<0.42.0>}
iex> Example.foo()
:ok # NOTE that by default, all logs are disabled by LoggerIexBackend
iex> LoggerIexBackend.set_rules(allow: :info)
:ok
iex> Example.foo()
:ok # No logs here yet
iex> Example.Bar.bar()
:ok
00:00:02.000 [info]  A bar message
iex> LoggerIexBackend.set_rules(allow: ~r/foo/) # Enable logs by message
iex> LoggerIexBackend.set_rules(allow: [module: Example]) # Enable logs by module
:ok
iex> Example.foo()
:ok
00:00:03.000 [debug] A foo message

Using LoggerIexBackend with IEx

To use LoggerIexBackend in your projects, first add LoggerIexBackend as a dependency.

def deps do
  [
    {:ex_doc, "~> 1.0", only: :dev}
  ]
end

Then, after installing the library using mix deps.get we have call LoggerIexBackend.start/0 to start using it.

We can also enable IEx log backend by default in interactive shell sessions of our projects using .iex.exs:

if :erlang.function_exported(LoggerIexBackend, :start, 0) do
  LoggerIexBackend.start()
end