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Yell Gem Version Build Status Code Climate Coverage Status

Yell - Your Extensible Logging Library is a comprehensive logging replacement for Ruby.

Yell works and its test suite currently runs on:

  • ruby-head, 2.3.1, 2.2.5, 2.2.2, 2.1.0, 2.0.0
  • jruby-head, jruby-, jruby-

If you want to conveniently use Yell with Rails, then head over to yell-rails. You'll find all the documentation in this repository, though.


System wide:

gem install yell

Or in your Gemfile:

gem "yell"


On the basics, you can use Yell just like any other logging library with a more sophisticated message formatter.

logger = STDOUT "Hello World"
#=> "2012-02-29T09:30:00+01:00 [ INFO] 65784 : Hello World"
#    ^                         ^       ^       ^
#    ISO8601 Timestamp         Level   Pid     Message

The strength of Yell, however, comes when using multiple adapters. The already built-in ones are IO-based and require no further configuration. Also, there are additional ones available as separate gems. Please consult the wiki on that - they are listed there.

The standard adapters are:

:stdout : Messages will be written to STDOUT
:stderr : Messages will be written to STDERR
:file : Messages will be written to a file
:datefile : Messages will be written to a timestamped file

Here are some short examples on how to combine them:

Example: Notice messages go into STDOUT and error messages into STDERR
logger = do |l|
  l.adapter STDOUT, level: [:debug, :info, :warn]
  l.adapter STDERR, level: [:error, :fatal]
Example: Typical production Logger

We setup a logger that starts passing messages at the :info level. Severities below :error go into the 'production.log', whereas anything higher is written into the 'error.log'.

logger = do |l|
  l.level = '' # will only pass :info and above to the adapters

  l.adapter :datefile, 'production.log', level: 'lte.warn' # anything lower or equal to :warn
  l.adapter :datefile, 'error.log', level: 'gte.error' # anything greater or equal to :error
Example: Typical production Logger for Heroku

When deploying to Heroku, the "rails_log_stdout" gem gets injected to your Rails project. Yell does not need that when properly configured (see yell-rails for a more convenient integration with Rails).

logger = do |l|
  l.level = ''

  l.adapter :stdout, level: 'lte.warn'
  l.adapter :stderr, level: 'gte.error'

But I'm used to Log4r and I don't want to move on

One of the really nice features of Log4r is its repository. The following example is taken from the official Log4r documentation.

require 'log4r'
include Log4r

# create a logger named 'mylog' that logs to stdout
mylog = 'mylog'
mylog.outputters = Outputter.stdout

# later in the code, you can get the logger back

With Yell you can do the same thing with less:

require 'yell'

# create a logger named 'mylog' that logs to stdout :stdout, name: 'mylog'

# later in the code, you can get the logger back

There is no need to define outputters separately and you don't have to taint you global namespace with Yell's subclasses.

Adding a logger to an existing class

Yell comes with a simple module: +Yell::Loggable+. Simply include this in a class and you are good to go.

# Before you can use it, you will need to define a logger and 
# provide it with the `:name` of your class. :stdout, name: 'Foo'

class Foo
  include Yell::Loggable

# Now you can log "Hello World" "Hello World"

It even works with class inheritance:

# Given the above example, we inherit from Foo
class Bar < Foo

# The logger will fallback to the Foo superclass "Hello World" "Hello World"

Adding a logger to all classes at once (global logger)

Derived from the example above, simply do the following.

# Define a logger and pass `Object` as name. Internally, Yell adds this
# logger to the repository where you can access it later on. :stdout, name: Object

# Enable logging for the class that (almost) every Ruby class inherits from
Object.send :include, Yell::Loggable

# now you are good to go... from wherever you are "Hello from anything" "Hello from Integer"

Suppress log messages with silencers

In case you woul like to suppress certain log messages, you may define silencers with Yell. Use this to get control of a noisy log environment. For instance, you can suppress logging messages that contain secure information or more simply, to skip information about serving your Rails assets. Provide a string or a regular expression of the message patterns you would like to exclude.

logger = do |l|
  l.silence /^Started GET "\/assets/
  l.silence /^Served asset/

logger.debug 'Started GET "/assets/logo.png" for at 2013-06-20 10:18:38 +0200'
logger.debug 'Served asset /logo.png - 304 Not Modified (0ms)'

Alter log messages with modifiers

Further Readings

How To: Setting The Log Level
How To: Formatting Log Messages
How To: Using Adapters
How To: The Datefile Adapter
How To: Different Adapters for Different Log Levels

Additional Adapters

Graylog2 (GELF)


How To: Writing Your Own Adapter

You can find further examples and additional adapters in the wiki. or have a look into the examples folder.

Copyright © 2011-2015 Rudolf Schmidt, released under the MIT license