This page explains how to integrate multi-level logging in Ruby, using ruby's builtin Logger library

It also describes two extensions provided by utilrb

Ruby basic logger

The Ruby logger is a simple multi-level logging library

The API is documented here: ​http://ruby-doc.org/stdlib-1.8.7 (click on the Logger class for a quick usage summary)

Logger usage in Rock's ruby packages

The usage is to have at least a logger per library, that is available at the main namespace (i.e. Ruby module). For instance, the root logger in orocos.rb is

Orocos.logger

Utilrb provides an easy way to define this logger:

require 'utilrb/logger'
module Orocos
  extend Logger::Root('orocos.rb', Logger::WARN)
end

This does two things

1. defines Orocos.logger and provides an initial setup for it. The program name and default logging level are provided as argument to Root
2. provides forwarding methods from Orocos to Orocos.logger, i.e. one can do

   Orocos.warn("message")
   

instead of

Orocos.logger.warn("message")

Hierarchical logger definition

Utilrb provides an extension that allows to share loggers in a hierarchical manner, for instance:

require 'utilrb/logger'
module Orocos
  extend Logger::Root
  module Roby
    extend Logger::Hierarchy
  end
end

Then, by default

Orocos::Roby.logger

will be equal to

Orocos.logger

i.e. if one does

Orocos::Roby.logger.level = Logger::INFO

Then the new level applies to Orocos.logger as well

To separate them, i.e. to create a separate logger at the level of Orocos::Roby simply do

Orocos::Roby.make_own_logger

The initially created logger will be setup the same way than Orocos.logger. You can then change that setup independently from the one in Orocos. For instance:

module Orocos
  extend Logger::Root('orocos.rb', Logger::WARN)
  module Roby
    extend Logger::Hierarchy
    logger.level = Logger::INFO
    # Both Orocos and Orocos::Roby have loggers at
    # Logger::INFO

    make_own_logger
    logger.level = Logger::DEBUG
    # Orocos.logger has a level of Logger::INFO and
    # Orocos::Roby.logger has a level of Logger::DEBUG
  end
end

Additionally, a new progname and level can be given directly to make_own_logger:

module Orocos
  extend Logger::Root('orocos.rb', Logger::WARN)
  module Roby
    extend Logger::Hierarchy
    make_own_logger("Orocos::Roby", Logger::DEBUG)
  end
end

The separated logger can be removed with

Orocos::Roby.reset_own_logger