FileOnly Logger

A simple logger that writes messages to log files only (not to the console). Elixir's Logger Backends were abandoned in favor of Erlang's Logger handlers.

Installation

Add file_only_logger to your list of dependencies in mix.exs:

def deps do
  [
    {:file_only_logger, "~> 0.2.0"}
  ]
end

Logger configuration may but does not have to be set via config files. See files config/config.exs and config/config_logger.exs as an example (including log file rotation).

In the absence of any configuration, the default handler (:default) will feature the following colors:

Level Color
:debug :light_cyan
:info :light_green
:warning :light_yellow
:error :light_red

Likewise without any configuration, the handlers below will log to their corresponding files with a log rotation of 5:

Level Handler File
:debug :debug_handler "./log/debug.log"
:info :info_handler "./log/info.log"
:warning :warning_handler "./log/warning.log"
:error :error_handler "./log/error.log"

Usage

Trying to log any message with severity less than the configured level will simply cause the message to be ignored.

The configuration values for log level are:

You may use file config/runtime.exs to configure the above log level:

import Config

config :file_only_logger, level: :info

Example

defmodule Log do
  use File.Only.Logger

  warning :error_occurred, {reason, file, env} do
    """
    \n'error' occurred...
    • Reason => '#{:file.format_error(reason)}'
    • File => #{Path.expand(file) |> inspect() |> maybe_break(10)}
    #{from(env, __MODULE__)}\
    """
  end
end

defmodule Check do
  def log_warning(file) do
    Log.warning(:error_occurred, {:enoent, file, __ENV__})
  end
end

Check.log_warning(__ENV__.file)
Check.log_warning("generate-line-break")
# will respectively log these lines in the configured log file(s):

2025-01-13 12:27:14.532 [warning]
'error' occurred...
• Reason => 'no such file or directory'
• File => "c:/Users/Ray/Documents/ex_dev/projects/file_only_logger/iex"
• App: undefined
• Module: Log
• Function: Check.log_warning/1

2025-01-13 12:30:46.370 [warning]
'error' occurred...
• Reason => 'no such file or directory'
• File =>
  "c:/Users/Ray/Documents/ex_dev/projects/file_only_logger/generate-line-break"
• App: undefined
• Module: Log
• Function: Check.log_warning/1

Note

If you'd like to write a message to both the log files and the console, simply change the macro to a function like so...

Example

defmodule Log do
  use File.Only.Logger

  require Logger

  def warning(:error_occurred, {reason, file, env}) do
    Logger.warning("""
    \n'error' occurred...
    • Reason => '#{:file.format_error(reason)}'
    • File => #{Path.expand(file) |> inspect() |> maybe_break(10)}
    #{from(env, __MODULE__)}\
    """)
  end
end