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Make Logging Easy in Ruby With Log4r

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Log4r is a Ruby gem that features a heirachical logging system of any number of levels, custom level names, multiple output destinations per log event, custom formatting, and more. The Log4r gem is open sourced on GitHub, and with comphrehensive documentations available on Rubyforge.

I have been using log4r at work in most of the applications and systems written in Ruby. It’s easy to use, and provide the features that an application would need: - Support multiple message levels such as Fatal, Error, Warn and Msg.
- Customizable log file format - Multiple output destinations, like print out on the screen, and store in a log file

Here in this post, I’ll show you how to use log4r in your Ruby project.

Step 1. Install Gem log4r

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gem install log4r

Step 2: Include log4r in your project

One thing to note is the log4r supports configurations through YAML file, and you can define the configuration file when including the log4r.

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require 'log4r'
require 'log4r/yamlconfigurator'
require 'log4r/outputter/datefileoutputter'
require 'log4r/outputter/emailoutputter'
include Log4r
ycfg = YamlConfigurator    # handy shorthand
ycfg.load_yaml_file(File.dirname(__FILE__)+'/l4r.yml')

Step 3: Configure log4r with a config file

You can define the logging levels, logger names, output destinations, etc. The following code shows an example of the configurations that I use.

File name: log4r.yml

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description: config file for log4r

---
# *** YAML2LOG4R ***
log4r_config:
  # define all pre config ...
  pre_config:
    global:
      level: DEBUG
    root  :
      level: DEBUG

  # define all loggers ...
  loggers:
    - name      : myproject
      level     : DEBUG
      additive  : 'false'
      trace     : 'false'
      outputters:
        - stderr
        - logfile
        - email


  # define all outputters (incl. formatters)
  outputters:
    - type     : StderrOutputter
      name     : stderr
      level    : INFO
      formatter:
        date_pattern: #'%y%m%d %H:%M:%S'
        pattern     : '[%c] %l: %m'
        type        : PatternFormatter

    - type        : DateFileOutputter
      name        : logfile
      level       : DEBUG
      date_pattern: #'%Y%m%d'
      trunc       : 'false'
      dirname     : "."
      formatter   :
        date_pattern: '%H:%M:%S'
        pattern     : '[%c] %d %l: %m'
        type        : PatternFormatter

    - type        : EmailOutputter
      name        : email
      level       : FATAL
      server      : <server domain>
      subject     : 'Message myproject:'
      from        : <email address>
      to          : <email address>
      formatter   :
        date_pattern: #'%y%m%d %H:%M:%S'
        pattern     : '%d %l: %m'
        type        : PatternFormatter
---

Step 4: Initialize a logger

You need initialize a logger in your project first.

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logger = Log4r::Logger['myproject']

Step 5: Use your logger

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logger.info 'My Project Starts!'
logger.warn 'Here is a warning'
logger.error 'Here is an error'
logger.fatal 'Fatal error happens. Program will exit'

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