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Grizzled Rails Logger is a Ruby gem that provides an add-on for the stock Rails 3 logger.

The Grizzled::Rails::Logger module augments the Rails 3 ActiveSupport::BufferedLogger class, providing some additional capabilities, including:

Installation for Rails 3

Add the following to your Gemfile, and run bundle install:

gem 'grizzled-rails-logger'

If you want the development version of the gem, use:

gem 'grizzled-rails-logger', :git => 'git://github.com/bmc/grizzled-rails-logger.git'

This gem is specific to Rails 3, but it should work fine with either Ruby 1.9 or Ruby 1.8.7.


Because Grizzled Rails Logger merely adds to the standard Rails logger, you can continue to all the usual capabilities of the Rails logger (such as, for instance, tagged logged).

To configure Grizzled Rails Logger, add a section like the following to your config/application.rb file, an individual environment file, or an initializer (e.g., config/initializers/logging.rb):

Grizzled::Rails::Logger.configure do |cfg|
  # Configuration data goes here

Note that this section stands by itself; it doesn’t go inside your class Application < Rails::Application configuration block. For simplicity and ease of maintenance, I recommend using a separate initializer file, like config/initializers/logging.rb.

If you configure it in application.rb or in an initializer file, you don’t need to require the module. If you configure it in your config/environments/whatever.rb file, however, you’ll also need the appropriate require statement at the top:

require 'grizzled/rails/logger'

The default configuration is equivalent to the following:

Grizzled::Rails::Logger.configure do |cfg|
  cfg.flatten = true
  cfg.flatten_patterns = [
  cfg.dont_flatten_patterns = [
  cfg.format = '[%T] (%S) %P %M'
  cfg.timeformat = '%Y/%m/%d %H:%M:%S'
  cfg.colorize = true
  cfg.colors = {
    :debug => Term::ANSIColor.cyan,
    :warn  => Term::ANSIColor.yellow + Term::ANSIColor.bold,
    :fatal => Term::ANSIColor.red + Term::ANSIColor.bold,
    :error => Term::ANSIColor.red

Each configuration option is described in more detail, below.


By default, Grizzled Rails Logger colorizes logging output, using ANSI terminal escape sequences (as defined by the term-ansicolor gem).

You can disable colorization by setting the colorize option to false:

Grizzled::Rails::Logger.configure do |cfg|
  cfg.colorize = false

You can also change the colors associated with each severity. Suppose, for instance, that you want INFO messages (which normally aren’t colorized) to be white, and you wanted DEBUG messages (which are normally cyan) to be bold blue. You’d simply reconfigure those values, as shown below:

Grizzled::Rails::Logger.configure do |cfg|
  cfg.colors[:debug] = Term::ANSIColor.bold + Term::ANSIColor.blue
  cfg.colors[:info] = Term::ANSIColor.white

Term::ANSIColor is automatically included for you.

WARNING: Grizzled Rails Logger does not verify that the values you store in the color settings are legal ANSI sequences. The following is perfectly legal, though probably not what you want:

Grizzled::Rails::Logger.configure do |cfg|
  cfg.colors[:debug] = "red"

With that (erroneous) setting, a debug message that normally looks like this:

[2012/04/12 14:43:22] (DEBUG) 9816 My debug message

will, instead, look like this:

red[2012/04/12 14:43:22] (DEBUG) 9816 My debug message

If what you want is this:

[2012/04/12 14:43:22] (DEBUG) 9816 My debug message


Grizzled::Rails::Logger.configure do |cfg|
  cfg.colors[:debug] = Term::ANSIColor.red

Exception logging

Grizzled Rails Logger adds an exception() method, providing an easy way to dump a rescued exception and its backtrace:

  # Some dangerous operation
rescue Exception => ex
  logger.exception("Error while doing dangerous thing", ex)

The method takes three parameters, one of which is optional:

The exception is dumped at severity level ERROR.

Regardless of the setting of flatten (see below), the exception’s backtrace is always displayed on multiple lines.


The default Rails logger includes lots of newlines in its log messages. For example:

[2012/04/12 14:59:48] (INFO) 10102 [659d08c8cbcf3ddf543ca3710cee2771] 

Started GET "/about" for at 2012-04-12 14:59:48 -0400

Grizzled Rails Logger automatically flattens log messages to a single line:

[2012/04/12 14:59:48] (INFO) 10102 [659d08c8cbcf3ddf543ca3710cee2771] Started GET "/about" for at 2012-04-12 14:59:48 -0400

If you prefer not to flatten log messages, disable the flatten setting:

 Grizzled::Rails::Logger.configure do |cfg|
  cfg.flatten = false

You can also flatten just some of the messages, by specifying a combination of flattening patterns and “don’t flatten” patterns. The default set of flattening patterns flattens all messages with embedded newlines. However, this strategy can be problematic, in that it’ll also flatten EXPLAIN PLAN output and some exceptions. To control which messages are flattened, define an array of regular expressions, matched against each message as if it were already flattened. (That is, the regexps do not need to take newlines into account.) For example:

Grizzled::Rails::Logger.configure do |cfg|
  cfg.flatten_patterns = [
    /.*Started GET /,
    /.*Started POST /

You can exert even more control by defining “don’t flatten” patterns, which take higher priority than “flatten” patterns. For instance, the following configuration flattens every message except those with the words “EXPLAIN PLAN” in them.

Grizzled::Rails::Logger.configure do |cfg|
  cfg.flatten_patterns = [
  cfg.dont_flatten_patterns = [

Unflattening Exceptions

Exception backtraces emitted via logger.exception() are never flattened.

However, since logger.exception() is a Grizzled Rails Logger extension, most components don’t use it. With the default configuration, exceptions logged through logger.error() are flattened, which is rather ugly.

The following patterns will match most exceptions, ensuring that they aren’t flattened in the log output. (They’re not part of the default configuration, however, because not everyone wants this behavior.)

Grizzled::Rails::Logger.configure do |cfg|
  cfg.dont_flatten_patterns = [
    /rb:\d+: syntax error/


Two settings control formatting.

Message format

The format setting controls overall message formatting. Four escape sequences control how the message is assembled:

Any other characters, including blanks, are emitted verbatim.

It’s legal (but probably silly) to include a sequence multiple times. If you don’t want a specific value to be logged, simply omit its escape sequence from the format.

The default format is: [%T] (%S) %P %M.

For example, to change the log format to omit the PID, use:

Grizzled::Rails::Logger.configure do |cfg|
  cfg.format = '[%T] (%S) %M'

Time format

The timeformat setting controls how the current time (see “%T”, above) is formatted. timeformat is a strftime format string.

The default time format is: %Y/%m/%d %H:%M:%S. If you only want to log the time (not the date), you can change it easily, in an intializer block:

Grizzled::Rails::Logger.configure do |cfg|
  cfg.timeformat = '%H:%M:%S'

Additional Fields and Rails Tagged Logging

Grizzled Rails Logger works in tandem with Rails 3.2 Tagged Logging, so you can also mix log tags into your log output. For instance, suppose you want to capture the user name, session ID, and remote IP address for the request that’s active when a message is logged. Grizzled Rails Logger doesn’t support escapes for those values, but you can use tagged logging to get them into your log messages. Make sure your environment initialization file contains lines such as the following:

MyApp::Application.configure do
  config.log_tags = [
    proc { |req| req.session[:id] || "no session },
    proc { |req| req.session[:user_name] || "anonymous" }

Grizzled Rails Logger will format the actual log message, and hand it off to the underlying Rails logger, which will add the log tags to it.


Because it uses the term-ansicolor gem, Grizzled Rails Logger effectively reserves the name Term, preventing you from using it. There are at least two known consequences of this:

First, if you have an existing Rails model called Term, you will not be able to use this gem unless you rename the model.

Second, if you use this gem and later attempt to create a model called Term, you’ll get the following error:

$ rails g model term name:string   
      invoke  active_record
The name 'Term' is either already used in your application or reserved by
Ruby on Rails. Please choose an alternative and run this generator again.

Currently, there’s no workaround for this issue.

Change log

The change log for this software is here.


Alternatives to Grizzled Rails Logger include Paul Dowman’s better_logging gem.


This software is copyright © 2012 Brian M. Clapper. It is released under a BSD license.