Custom Formatters

The formatting for each appender can be replaced with custom code. To replace the existing formatter supply a block of code when creating the appender.

The formatter proc receives a single parameter which is the entire Log Struct. For the format of the Log Struct, see Log Struct

Example: Formatter that just returns the Log Struct

require "semantic_logger"

SemanticLogger.default_level = :trace

formatter = Proc.new do |log|
  # This formatter just returns the log struct as a string
  log.inspect
end
SemanticLogger.add_appender(io: $stdout, formatter: formatter)

logger = SemanticLogger["Hello"]
logger.info "Hello World"

Output:

#<struct SemanticLogger::Log level=:info, thread_name=70167090649820, name="Hello", message="Hello World", payload=nil, time=2012-10-24 10:09:33 -0400, duration=nil, tags=nil, level_index=2>

Example: Replace the default log file formatter

require "semantic_logger"
SemanticLogger.default_level = :trace

Create a custom formatter:

class MyFormatter < SemanticLogger::Formatters::Default
  # Return the complete log level name in uppercase
  def level
    log.level.upcase
  end
end

Specify the formatter when creating the appender:

SemanticLogger.add_appender(file_name: "development.log", formatter: MyFormatter.new)

Example usage:

Rails.logger.info "Hello World"

# => 2017-04-05 01:05:52.868286 INFO [13143:70216759638540 (irb):11] Rails -- Hello World

See SemanticLogger::Formatters::Default for all the methods that can be replaced to customize the output.

Example: Replace the colorized log file formatter

require "semantic_logger"
SemanticLogger.default_level = :trace

Create a custom formatter:

class MyFormatter < SemanticLogger::Formatters::Color
  # Return the complete log level name in uppercase
  def level
    "#{color}log.level.upcase#{clear}"
  end
end

Specify the formatter when creating the appender:

SemanticLogger.add_appender(file_name: "development.log", formatter: MyFormatter.new)

Example usage:

Rails.logger.info "Hello World"

# => 2017-04-05 01:05:52.868286 INFO [13143:70216759638540 (irb):11] Rails -- Hello World

See SemanticLogger::Formatters::Color for all the methods that can be replaced to customize the output.

Example: Replacing the format for an active logger, such as in Rails:

This example assumes you have gem "rails_semantic_logger" in your Gemfile.

Create a file called config/initializers/semantic_logger.rb:

# Find file appender:
appender = SemanticLogger.appenders.find{ |a| a.is_a?(SemanticLogger::Appender::File) }

appender.formatter = MyFormatter.new

Example: Do not log the process ID

When running docker containers with a single process which is always 1, or when running only one process on a server the PID ( Process ID ) is not relevant.

To leave out the pid, we can use a custom formatter:

class NoPidFormatter < SemanticLogger::Formatters::Default
  # Leave out the pid
  def pid
  end
end

Specify the formatter when creating the appender:

SemanticLogger.add_appender(file_name: "development.log", formatter: NoPidFormatter.new)

Or to use the colorized formatter, use SemanticLogger::Formatters::Color instead of SemanticLogger::Formatters::Default.

Or if the appender is already installed:

SemanticLogger.appenders.first.formatter = NoPidFormatter.new

Next: Custom Appenders ==>