How To Log In Ruby

Logging is an essential part of the development process, as it allows developers to track the execution of their code, debug issues, and monitor performance. In this blog post, we will go through the basics of logging in Ruby, using the built-in Logger class and the standard Ruby logging methods.

Using the Logger Class

In Ruby, the Logger class is part of the standard library and provides a simple yet powerful logging mechanism. To start using the Logger class, you will first need to require it in your Ruby file:

require 'logger'

Once you have required the Logger class, you can create a new logger instance and start logging messages. By default, the Logger will output messages to STDOUT, but you can also provide a file path to log messages to a file:

logger =
logger ='logfile.log')

The Logger class provides various logging methods based on severity levels, which are:

  • debug: Debugging information, useful for developers.
  • info: General information about the running process.
  • warn: A warning message indicating a potential issue.
  • error: An error message indicating something went wrong during the process.
  • fatal: A critical error message indicating the process cannot continue.

Here’s an example of using the various logging methods:

logger.debug("This is a debug message")"This is an info message")
logger.warn("This is a warning message")
logger.error("This is an error message")
logger.fatal("This is a fatal message")

Configuring the Logger

The Logger class provides several options to configure its behavior. One of the most common settings is the log level, which determines the minimum severity level of messages that will be logged. For example, if you set the log level to Logger::WARN, only warnings, errors, and fatal messages will be logged:

logger.level = Logger::WARN

Here’s an overview of the available log levels:

  • Logger::DEBUG
  • Logger::INFO
  • Logger::WARN
  • Logger::ERROR
  • Logger::FATAL

Another useful configuration option is the log formatter. The default formatter displays the log message with the date, time, severity level, and process ID. You can customize the formatter by providing a block that takes the severity, timestamp, process ID, and message as its arguments:

logger.formatter = proc do |severity, datetime, progname, msg|
  "#{datetime}: #{severity} [#{progname}]: #{msg}\n"


In this blog post, we covered the basics of logging in Ruby using the built-in Logger class. By using the Logger class and its various configuration options, you can effectively track the execution of your code, debug issues, and monitor performance in your Ruby applications.