Logging

Charming applications have a logger available from the application and from controllers.

By default, the logger writes to File::NULL, which is the operating system’s null device. Logging calls are safe to make, but no file is created and nothing is printed to the terminal.

logger.info("Loaded todos")
logger.debug("Current route: #{route.path}")

Configure A Logger

Configure a logger on your application class:

require "fileutils"
require "logger"

class MyApp::Application < Charming::Application
  root File.expand_path("../..", __dir__)

  FileUtils.mkdir_p(File.join(root, "log"))
  logger Logger.new(File.join(root, "log", "app.log"))
end

Controllers access the configured application logger through logger:

class MyApp::HomeController < MyApp::ApplicationController
  def show
    logger.info("Rendering home screen")
    render :show
  end
end

Override At Runtime

Applications can also replace the logger before running:

app = MyApp::Application.new
app.logger = Logger.new(options.fetch(:log_file))

Charming.run(app)

This is useful when your executable exposes its own --log-file option or reads a user config file.

Avoid Terminal Streams

Avoid logging to $stdout or $stderr while the TUI is running. Charming renders into an alternate terminal screen, and writing ordinary log output to the terminal can corrupt the interface.

Prefer file logging:

FileUtils.mkdir_p(File.join(root, "log"))
logger Logger.new(File.join(root, "log", "app.log"))

Or keep the default null logger when you do not need logs.

Default Behavior

The default logger is equivalent to:

Logger.new(File::NULL)

File::NULL maps to /dev/null on macOS and Linux, and NUL on Windows.