In Files

  • logger.rb

Logger

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 22283 2009-02-13 10:18:12Z shyouhei $

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.

Constants

ProgName
SEV_LABEL

Severity label for logging. (max 5 char)

VERSION

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.

sev_threshold[RW]

Logging severity threshold (e.g. Logger::INFO).

sev_threshold=[RW]

Logging severity threshold (e.g. Logger::INFO).

Public Class Methods

new(logdev, shift_age = 0, shift_size = 1048576) click to toggle source

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.

 
               # File logger.rb, line 256
def initialize(logdev, shift_age = 0, shift_size = 1048576)
  @progname = nil
  @level = DEBUG
  @default_formatter = Formatter.new
  @formatter = nil
  @logdev = nil
  if logdev
    @logdev = LogDevice.new(logdev, :shift_age => shift_age,
      :shift_size => shift_size)
  end
end
            

Public Instance Methods

<<(msg) click to toggle source

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

 
               # File logger.rb, line 336
def <<(msg)
  unless @logdev.nil?
    @logdev.write(msg)
  end
end
            
add(severity, message = nil, progname = nil, &block) click to toggle source

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.

 
               # File logger.rb, line 312
def add(severity, message = nil, progname = nil, &block)
  severity ||= UNKNOWN
  if @logdev.nil? or severity < @level
    return true
  end
  progname ||= @progname
  if message.nil?
    if block_given?
      message = yield
    else
      message = progname
      progname = @progname
    end
  end
  @logdev.write(
    format_message(format_severity(severity), Time.now, progname, message))
  true
end
            
Also aliased as: log
close() click to toggle source

Close the logging device.

 
               # File logger.rb, line 417
def close
  @logdev.close if @logdev
end
            
datetime_format() click to toggle source
 
               # File logger.rb, line 201
def datetime_format
  @default_formatter.datetime_format
end
            
datetime_format=(datetime_format) click to toggle source

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

 
               # File logger.rb, line 197
def datetime_format=(datetime_format)
  @default_formatter.datetime_format = datetime_format
end
            
debug(progname = nil, &block) click to toggle source

Log a DEBUG message.

See info for more information.

 
               # File logger.rb, line 347
def debug(progname = nil, &block)
  add(DEBUG, nil, progname, &block)
end
            
debug?() click to toggle source

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

 
               # File logger.rb, line 217
def debug?; @level <= DEBUG; end
            
error(progname = nil, &block) click to toggle source

Log an ERROR message.

See info for more information.

 
               # File logger.rb, line 391
def error(progname = nil, &block)
  add(ERROR, nil, progname, &block)
end
            
error?() click to toggle source

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

 
               # File logger.rb, line 229
def error?; @level <= ERROR; end
            
fatal(progname = nil, &block) click to toggle source

Log a FATAL message.

See info for more information.

 
               # File logger.rb, line 400
def fatal(progname = nil, &block)
  add(FATAL, nil, progname, &block)
end
            
fatal?() click to toggle source

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

 
               # File logger.rb, line 233
def fatal?; @level <= FATAL; end
            
info(progname = nil, &block) click to toggle source

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.

 
               # File logger.rb, line 373
def info(progname = nil, &block)
  add(INFO, nil, progname, &block)
end
            
info?() click to toggle source

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

 
               # File logger.rb, line 221
def info?; @level <= INFO; end
            
log(severity, message = nil, progname = nil, &block) click to toggle source
Alias for: add
unknown(progname = nil, &block) click to toggle source

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

See info for more information.

 
               # File logger.rb, line 410
def unknown(progname = nil, &block)
  add(UNKNOWN, nil, progname, &block)
end
            
warn(progname = nil, &block) click to toggle source

Log a WARN message.

See info for more information.

 
               # File logger.rb, line 382
def warn(progname = nil, &block)
  add(WARN, nil, progname, &block)
end
            
warn?() click to toggle source

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

 
               # File logger.rb, line 225
def warn?; @level <= WARN; end
            

Commenting is here to help enhance the documentation. For example, code samples, or clarification of the documentation.

If you have questions about Ruby or the documentation, please post to one of the Ruby mailing lists. You will get better, faster, help that way.

If you wish to post a correction of the docs, please do so, but also file bug report so that it can be corrected for the next release. Thank you.

If you want to help improve the Ruby documentation, please visit Documenting-ruby.org.

blog comments powered by Disqus