# Yell [![Gem Version](https://badge.fury.io/rb/yell.png)](http://badge.fury.io/rb/yell) [![Build Status](https://travis-ci.org/rudionrails/yell.png?branch=master)](https://travis-ci.org/rudionrails/yell) [![Code Climate](https://codeclimate.com/github/rudionrails/yell.png)](https://codeclimate.com/github/rudionrails/yell) [![Coverage Status](https://coveralls.io/repos/rudionrails/yell/badge.png?branch=master)](https://coveralls.io/r/rudionrails/yell)


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

Yell works and is tested with ruby 1.8.7, 1.9.x, 2.0.0, jruby 1.8 and 1.9 mode, rubinius 1.8 and 1.9 as well as ree.

If you want to conveniently use Yell with Rails, then head over to [yell-rails](https://github.com/rudionrails/yell-rails). You'll find all the documentation in this repository, though.


## Installation

System wide:

```console
gem install yell
```

Or in your Gemfile:

```ruby
gem "yell"
```


## Usage

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

```ruby
logger = Yell.new STDOUT

logger.info "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](https://github.com/rudionrails/yell/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`

```ruby
logger = Yell.new do |l|
  l.adapter STDOUT, level: [:debug, :info, :warn]
  l.adapter STDERR, level: [:error, :fatal]
end
```

##### 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'.

```ruby
logger = Yell.new do |l|
  l.level = 'gte.info' # 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
end
```

##### 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](https://github.com/rudionrails/yell-rails)
for a more convenient integration with Rails).

```ruby
logger = Yell.new do |l|
  l.level = 'gte.info'

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

### 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](http://log4r.rubyforge.org/manual.html#outofbox).

```ruby
require 'log4r'
include Log4r

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

# later in the code, you can get the logger back
Logger['mylog']
```

With Yell you can do the same thing with less:

```ruby
require 'yell'

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

# later in the code, you can get the logger back
Yell['mylog']
```

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.

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

class Foo
  include Yell::Loggable
end

# Now you can log
Foo.logger.info "Hello World"
Foo.new.logger.info "Hello World"
```

It even works with class inheritance:

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

# The logger will fallback to the Foo superclass
Bar.logger.info "Hello World"
Bar.new.logger.info "Hello World"
```

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

Derived from the example above, simply do the following.

```ruby
# Define a logger and pass `Object` as name. Internally, Yell adds this
# logger to the repository where you can access it later on.
Yell.new :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
logger.info "Hello from anything"
Integer.logger.info "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.

```ruby
logger = Yell.new do |l|
  l.silence /^Started GET "\/assets/
  l.silence /^Served asset/
end

logger.debug 'Started GET "/assets/logo.png" for 127.0.0.1 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](https://github.com/rudionrails/yell/wiki/101-setting-the-log-level)  
[How To: Formatting Log Messages](https://github.com/rudionrails/yell/wiki/101-formatting-log-messages)  
[How To: Using Adapters](https://github.com/rudionrails/yell/wiki/101-using-adapters)  
[How To: The Datefile Adapter](https://github.com/rudionrails/yell/wiki/101-the-datefile-adapter)  
[How To: Different Adapters for Different Log Levels](https://github.com/rudionrails/yell/wiki/101-different-adapters-for-different-log-levels)  


### Additional Adapters
[Syslog](https://github.com/rudionrails/yell/wiki/additional-adapters-syslog)  
[syslog-sd](https://github.com/raymond-wells/yell-adapters-syslogsd)  
[Graylog2 (GELF)](https://github.com/rudionrails/yell/wiki/additional-adapters-gelf)  
[Fluentd](https://github.com/red5studios/yell-adapters-fluentd)  


### Development

[How To: Writing Your Own Adapter](https://github.com/rudionrails/yell/wiki/Writing-your-own-adapter)  

You can find further examples and additional adapters in the [wiki](https://github.com/rudionrails/yell/wiki).
or have a look into the examples folder.


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

