Class Logger
In: lib/logger.rb
Parent: Object

Simple logging utility.

Author:NAKAMURA, Hiroshi <nakahiro@sarion.co.jp>
Documentation:NAKAMURA, Hiroshi and Gavin Sinclair
License:You can redistribute it and/or modify it under the same terms of Ruby‘s license; either the dual license version in 2003, or any later version.
Revision:$Id: logger.rb 31806 2011-05-30 02:08:57Z nahi $

Description

The Logger class provides a simple but sophisticated logging utility that anyone can use because it‘s included in the Ruby 1.8.x standard library.

The HOWTOs below give a code-based overview of Logger‘s usage, but the basic concept is as follows. You create a Logger object (output to a file or elsewhere), and use it to log messages. The messages will have varying levels (info, error, etc), reflecting their varying importance. The levels, and their meanings, are:

FATAL:an unhandleable error that results in a program crash
ERROR:a handleable error condition
WARN:a warning
INFO:generic (useful) information about system operation
DEBUG:low-level information for developers

So each message has a level, and the Logger itself has a level, which acts as a filter, so you can control the amount of information emitted from the logger without having to remove actual messages.

For instance, in a production system, you may have your logger(s) set to INFO (or WARN if you don‘t want the log files growing large with repetitive information). When you are developing it, though, you probably want to know about the program‘s internal state, and would set them to DEBUG.

Example

A simple example demonstrates the above explanation:

  log = Logger.new(STDOUT)
  log.level = Logger::WARN

  log.debug("Created logger")
  log.info("Program started")
  log.warn("Nothing to do!")

  begin
    File.each_line(path) do |line|
      unless line =~ /^(\w+) = (.*)$/
        log.error("Line in wrong format: #{line}")
      end
    end
  rescue => err
    log.fatal("Caught exception; exiting")
    log.fatal(err)
  end

Because the Logger‘s level is set to WARN, only the warning, error, and fatal messages are recorded. The debug and info messages are silently discarded.

Features

There are several interesting features that Logger provides, like auto-rolling of log files, setting the format of log messages, and specifying a program name in conjunction with the message. The next section shows you how to achieve these things.

HOWTOs

How to create a logger

The options below give you various choices, in more or less increasing complexity.

  1. Create a logger which logs messages to STDERR/STDOUT.
      logger = Logger.new(STDERR)
      logger = Logger.new(STDOUT)
    
  2. Create a logger for the file which has the specified name.
      logger = Logger.new('logfile.log')
    
  3. Create a logger for the specified file.
      file = File.open('foo.log', File::WRONLY | File::APPEND)
      # To create new (and to remove old) logfile, add File::CREAT like;
      #   file = open('foo.log', File::WRONLY | File::APPEND | File::CREAT)
      logger = Logger.new(file)
    
  4. Create a logger which ages logfile once it reaches a certain size. Leave 10 "old log files" and each file is about 1,024,000 bytes.
      logger = Logger.new('foo.log', 10, 1024000)
    
  5. Create a logger which ages logfile daily/weekly/monthly.
      logger = Logger.new('foo.log', 'daily')
      logger = Logger.new('foo.log', 'weekly')
      logger = Logger.new('foo.log', 'monthly')
    

How to log a message

Notice the different methods (fatal, error, info) being used to log messages of various levels. Other methods in this family are warn and debug. add is used below to log a message of an arbitrary (perhaps dynamic) level.

  1. Message in block.
      logger.fatal { "Argument 'foo' not given." }
    
  2. Message as a string.
      logger.error "Argument #{ @foo } mismatch."
    
  3. With progname.
      logger.info('initialize') { "Initializing..." }
    
  4. With severity.
      logger.add(Logger::FATAL) { 'Fatal error!' }
    

How to close a logger

     logger.close

Setting severity threshold

  1. Original interface.
      logger.sev_threshold = Logger::WARN
    
  2. Log4r (somewhat) compatible interface.
      logger.level = Logger::INFO
    
      DEBUG < INFO < WARN < ERROR < FATAL < UNKNOWN
    

Format

Log messages are rendered in the output stream in a certain format. The default format and a sample are shown below:

Log format:

  SeverityID, [Date Time mSec #pid] SeverityLabel -- ProgName: message

Log sample:

  I, [Wed Mar 03 02:34:24 JST 1999 895701 #19074]  INFO -- Main: info.

You may change the date and time format in this manner:

  logger.datetime_format = "%Y-%m-%d %H:%M:%S"
        # e.g. "2004-01-03 00:54:26"

There is currently no supported way to change the overall format, but you may have some luck hacking the Format constant.

Methods

<<   add   close   datetime_format   datetime_format=   debug   debug?   error   error?   fatal   fatal?   format_message   format_severity   info   info?   log   new   unknown   warn   warn?  

Included Modules

Severity

Classes and Modules

Module Logger::Severity
Class Logger::Application
Class Logger::Error
Class Logger::Formatter
Class Logger::LogDevice
Class Logger::ShiftingError

Constants

VERSION = "1.2.6"
ProgName = "#{File.basename(__FILE__)}/#{VERSION}"
SEV_LABEL = %w(DEBUG INFO WARN ERROR FATAL ANY)   Severity label for logging. (max 5 char)

External Aliases

level -> sev_threshold
level= -> sev_threshold=

Attributes

formatter  [RW]  Logging formatter. formatter#call is invoked with 4 arguments; severity, time, progname and msg for each log. Bear in mind that time is a Time and msg is an Object that user passed and it could not be a String. It is expected to return a logdev#write-able Object. Default formatter is used when no formatter is set.
level  [RW]  Logging severity threshold (e.g. Logger::INFO).
progname  [RW]  Logging program name.

Public Class methods

Synopsis

  Logger.new(name, shift_age = 7, shift_size = 1048576)
  Logger.new(name, shift_age = 'weekly')

Args

logdev:The log device. This is a filename (String) or IO object (typically STDOUT, STDERR, or an open file).
shift_age:Number of old log files to keep, or frequency of rotation (daily, weekly or monthly).
shift_size:Maximum logfile size (only applies when shift_age is a number).

Description

Create an instance.

[Source]

     # File lib/logger.rb, line 255
255:   def initialize(logdev, shift_age = 0, shift_size = 1048576)
256:     @progname = nil
257:     @level = DEBUG
258:     @default_formatter = Formatter.new
259:     @formatter = nil
260:     @logdev = nil
261:     if logdev
262:       @logdev = LogDevice.new(logdev, :shift_age => shift_age,
263:         :shift_size => shift_size)
264:     end
265:   end

Public Instance methods

Dump given message to the log device without any formatting. If no log device exists, return nil.

[Source]

     # File lib/logger.rb, line 335
335:   def <<(msg)
336:     unless @logdev.nil?
337:       @logdev.write(msg)
338:     end
339:   end

Synopsis

  Logger#add(severity, message = nil, progname = nil) { ... }

Args

severity:Severity. Constants are defined in Logger namespace: DEBUG, INFO, WARN, ERROR, FATAL, or UNKNOWN.
message:The log message. A String or Exception.
progname:Program name string. Can be omitted. Treated as a message if no message and block are given.
block:Can be omitted. Called to get a message string if message is nil.

Return

true if successful, false otherwise.

When the given severity is not high enough (for this particular logger), log no message, and return true.

Description

Log a message if the given severity is high enough. This is the generic logging method. Users will be more inclined to use debug, info, warn, error, and fatal.

Message format: message can be any object, but it has to be converted to a String in order to log it. Generally, inspect is used if the given object is not a String. A special case is an Exception object, which will be printed in detail, including message, class, and backtrace. See msg2str for the implementation if required.

Bugs

  • Logfile is not locked.
  • Append open does not need to lock file.
  • But on the OS which supports multi I/O, records possibly be mixed.

[Source]

     # File lib/logger.rb, line 311
311:   def add(severity, message = nil, progname = nil, &block)
312:     severity ||= UNKNOWN
313:     if @logdev.nil? or severity < @level
314:       return true
315:     end
316:     progname ||= @progname
317:     if message.nil?
318:       if block_given?
319:         message = yield
320:       else
321:         message = progname
322:         progname = @progname
323:       end
324:     end
325:     @logdev.write(
326:       format_message(format_severity(severity), Time.now, progname, message))
327:     true
328:   end

Close the logging device.

[Source]

     # File lib/logger.rb, line 416
416:   def close
417:     @logdev.close if @logdev
418:   end

[Source]

     # File lib/logger.rb, line 200
200:   def datetime_format
201:     @default_formatter.datetime_format
202:   end

Logging date-time format (string passed to strftime).

[Source]

     # File lib/logger.rb, line 196
196:   def datetime_format=(datetime_format)
197:     @default_formatter.datetime_format = datetime_format
198:   end

Log a DEBUG message.

See info for more information.

[Source]

     # File lib/logger.rb, line 346
346:   def debug(progname = nil, &block)
347:     add(DEBUG, nil, progname, &block)
348:   end

Returns true iff the current severity level allows for the printing of DEBUG messages.

[Source]

     # File lib/logger.rb, line 216
216:   def debug?; @level <= DEBUG; end

Log an ERROR message.

See info for more information.

[Source]

     # File lib/logger.rb, line 390
390:   def error(progname = nil, &block)
391:     add(ERROR, nil, progname, &block)
392:   end

Returns true iff the current severity level allows for the printing of ERROR messages.

[Source]

     # File lib/logger.rb, line 228
228:   def error?; @level <= ERROR; end

Log a FATAL message.

See info for more information.

[Source]

     # File lib/logger.rb, line 399
399:   def fatal(progname = nil, &block)
400:     add(FATAL, nil, progname, &block)
401:   end

Returns true iff the current severity level allows for the printing of FATAL messages.

[Source]

     # File lib/logger.rb, line 232
232:   def fatal?; @level <= FATAL; end

Log an INFO message.

The message can come either from the progname argument or the block. If both are provided, then the block is used as the message, and progname is used as the program name.

Examples

  logger.info("MainApp") { "Received connection from #{ip}" }
  # ...
  logger.info "Waiting for input from user"
  # ...
  logger.info { "User typed #{input}" }

You‘ll probably stick to the second form above, unless you want to provide a program name (which you can do with Logger#progname= as well).

Return

See add.

[Source]

     # File lib/logger.rb, line 372
372:   def info(progname = nil, &block)
373:     add(INFO, nil, progname, &block)
374:   end

Returns true iff the current severity level allows for the printing of INFO messages.

[Source]

     # File lib/logger.rb, line 220
220:   def info?; @level <= INFO; end
log(severity, message = nil, progname = nil, &block)

Alias for add

Log an UNKNOWN message. This will be printed no matter what the logger level.

See info for more information.

[Source]

     # File lib/logger.rb, line 409
409:   def unknown(progname = nil, &block)
410:     add(UNKNOWN, nil, progname, &block)
411:   end

Log a WARN message.

See info for more information.

[Source]

     # File lib/logger.rb, line 381
381:   def warn(progname = nil, &block)
382:     add(WARN, nil, progname, &block)
383:   end

Returns true iff the current severity level allows for the printing of WARN messages.

[Source]

     # File lib/logger.rb, line 224
224:   def warn?; @level <= WARN; end

Private Instance methods

[Source]

     # File lib/logger.rb, line 429
429:   def format_message(severity, datetime, progname, msg)
430:     (@formatter || @default_formatter).call(severity, datetime, progname, msg)
431:   end

[Source]

     # File lib/logger.rb, line 425
425:   def format_severity(severity)
426:     SEV_LABEL[severity] || 'ANY'
427:   end

[Validate]