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warn.rb

This Ruby code snippet demonstrates the use of the Logger class for logging messages. It initializes a logger to STDOUT, sets the logging level to WARN, and then logs messages at different levels (WARN, INFO, DEBUG) demonstrating how the level setting affects what is actually logged to the console.

Additional Note

Ref. https://docs.ruby-lang.org/ja/latest/library/logger.html

Ruby code snippet

require 'logger'
(irb):1: warning: logger was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add logger to your Gemfile or gemspec to silence this warning.
#=> true

logger = Logger.new(STDOUT)
#=> 
#<Logger:0x00007f0d50e26a30


puts "Level WARN"
Level WARN
#=> nil
logger.level = Logger::WARN # <= change level
#=> 2

logger.warn("Nothing to do!") # output
W, [2025-07-22T13:40:33.302916 #3036]  WARN -- : Nothing to do!
#=> true
logger.info("Program started") # none
#=> true
logger.debug("Created logger") # none
#=> true

Executed with Ruby 3.4.5.