Class: Logger (Ruby 2.4.0) (original) (raw)

Description¶ ↑

The Logger class provides a simple but sophisticated logging utility that you can use to output messages.

The messages have associated levels, such as INFO orERROR that indicate their importance. You can then give theLogger a level, and only messages at that level or higher will be printed.

The levels are:

UNKNOWN

An unknown message that should always be logged.

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.

For instance, in a production system, you may have your Logger set to INFO or evenWARN. When you are developing the system, however, you probably want to know about the program’s internal state, and would set theLogger to DEBUG.

Note: Logger does not escape or sanitize any messages passed to it. Developers should be aware of when potentially malicious data (user-input) is passed to Logger, and manually escape the untrusted data:

logger.info("User-input: #{input.dump}") logger.info("User-input: %p" % input)

You can use formatter= for escaping all data.

original_formatter = Logger::Formatter.new logger.formatter = proc { |severity, datetime, progname, msg| original_formatter.call(severity, datetime, progname, msg.dump) } logger.info(input)

Example¶ ↑

This creates a Logger that outputs to the standard output stream, with a level of WARN:

require 'logger'

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

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

path = "a_non_existent_file"

begin File.foreach(path) do |line| unless line =~ /^(\w+) = (.*)$/ logger.error("Line in wrong format: #{line.chomp}") end end rescue => err logger.fatal("Caught exception; exiting") logger.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)
   logger = Logger.new(file)
4. Create a logger which ages the logfile once it reaches a certain size. Leave 10 “old” log files where each file is about 1,024,000 bytes.
   logger = Logger.new('foo.log', 10, 1024000)
5. Create a logger which ages the 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 a 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!' }

The block form allows you to create potentially complex log messages, but to delay their evaluation until and unless the message is logged. For example, if we have the following:

logger.debug { "This is a " + potentially + " expensive operation" }

If the logger’s level is INFO or higher, no debug messages will be logged, and the entire block will not even be evaluated. Compare to this:

logger.debug("This is a " + potentially + " expensive operation")

Here, the string concatenation is done every time, even if the log level is not set to show the debug message.

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
3. Symbol or String (case insensitive)
   logger.level = :info
   logger.level = 'INFO'
4. Constructor
   Logger.new(logdev, level: Logger::INFO)
   Logger.new(logdev, level: :info)
   Logger.new(logdev, level: 'INFO')

Format¶ ↑

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

Log format:

SeverityID, [DateTime #pid] SeverityLabel -- ProgName: message

Log sample:

I, [1999-03-03T02:34:24.895701 #19074] INFO -- Main: info.

You may change the date and time format via datetime_format=.

logger.datetime_format = '%Y-%m-%d %H:%M:%S'

or via the constructor.

Logger.new(logdev, datetime_format: '%Y-%m-%d %H:%M:%S')

Or, you may change the overall format via the formatter= method.

logger.formatter = proc do |severity, datetime, progname, msg| "#{datetime}: #{msg}\n" end

or via the constructor.

Logger.new(logdev, formatter: proc {|severity, datetime, progname, msg| "#{datetime}: #{msg}\n" })

not used after 1.2.7. just for compat.

frozen_string_literal: true

frozen_string_literal: true

frozen_string_literal: true

frozen_string_literal: true

formatter[RW]

Logging formatter, as a Proc that will take four arguments and return the formatted message. The arguments are:

severity

The Severity of the log message.

time

A Time instance representing when the message was logged.

progname

The progname configured, or passed to the logger method.

msg

The Object the user passed to the log message; not necessarily a String.

The block should return an Object that can be written to the logging device via write. The default formatter is used when no formatter is set.

level[R]

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

progname[RW]

Program name to include in log messages.

sev_threshold[R]

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

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

new(logdev, shift_age = 'weekly')

new(logdev, level: :info)

new(logdev, progname: 'progname')

new(logdev, formatter: formatter)

new(logdev, datetime_format: '%Y-%m-%d %H:%M:%S')

Args¶ ↑

logdev

The log device. This is a filename (String) or IO object (typicallySTDOUT, STDERR, or an open file).

shift_age

Number of old log files to keep, or frequency of rotation (daily, weekly or monthly). Default value is 0, which disables log file rotation.

shift_size

Maximum logfile size in bytes (only applies when shift_age is a positive Integer). Defaults to 1048576 (1MB).

level

Logging severity threshold. Default values is Logger::DEBUG.

progname

Program name to include in log messages. Default value is nil.

formatter

Logging formatter. Default values is an instance of Logger::Formatter.

datetime_format

Date and time format. Default value is ‘%Y-%m-%d %H:%M:%S’.

binmode

Use binary mode on the log device. Default value is false.

shift_period_suffix

The log file suffix format for daily, weekly ormonthly rotation. Default is ‘%Y%m%d’.

Description¶ ↑

Create an instance.

def initialize(logdev, shift_age = 0, shift_size = 1048576, level: DEBUG, progname: nil, formatter: nil, datetime_format: nil, binmode: false, shift_period_suffix: '%Y%m%d') self.level = level self.progname = progname @default_formatter = Formatter.new self.datetime_format = datetime_format self.formatter = formatter @logdev = nil if logdev @logdev = LogDevice.new(logdev, shift_age: shift_age, shift_size: shift_size, shift_period_suffix: shift_period_suffix, binmode: binmode) end end

<<(msg) click to toggle source

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

def <<(msg) @logdev&.write(msg) end

Logger#add(severity, message = nil, progname = nil) { ... } click to toggle source

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 nomessage and block are given.

block

Can be omitted. Called to get a message string if message is nil.

Return¶ ↑

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.
• If the OS supports multi I/O, records possibly may be mixed.

def add(severity, message = nil, progname = nil) severity ||= UNKNOWN if @logdev.nil? or severity < level return true end if progname.nil? progname = @progname end 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.

def close @logdev&.close end

datetime_format() click to toggle source

Returns the date format being used. See datetime_format=

def datetime_format @default_formatter.datetime_format end

datetime_format=(datetime_format) click to toggle source

Set date-time format.

datetime_format

A string suitable for passing to strftime.

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.

def debug(progname = nil, &block) add(DEBUG, nil, progname, &block) end

debug!() click to toggle source

Sets the severity to DEBUG.

def debug!; self.level = DEBUG; end

debug?() click to toggle source

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

def debug?; level <= DEBUG; end

error(progname = nil, &block) click to toggle source

Log an ERROR message.

See info for more information.

def error(progname = nil, &block) add(ERROR, nil, progname, &block) end

error!() click to toggle source

Sets the severity to ERROR.

def error!; self.level = ERROR; end

error?() click to toggle source

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

def error?; level <= ERROR; end

fatal(progname = nil, &block) click to toggle source

Log a FATAL message.

See info for more information.

def fatal(progname = nil, &block) add(FATAL, nil, progname, &block) end

fatal!() click to toggle source

Sets the severity to FATAL.

def fatal!; self.level = FATAL; end

fatal?() click to toggle source

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

def fatal?; level <= FATAL; end

info(message) click to toggle source

info(progname, &block)

Log an INFO message.

message

The message to log; does not need to be a String.

progname

In the block form, this is the progname to use in the log message. The default can be set with progname=.

block

Evaluates to the message to log. This is not evaluated unless the logger’s level is sufficient to log the message. This allows you to create potentially expensive logging messages that are only called when the logger is configured to show them.

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 progname= as well).

Return¶ ↑

See add.

def info(progname = nil, &block) add(INFO, nil, progname, &block) end

info!() click to toggle source

Sets the severity to INFO.

def info!; self.level = INFO; end

info?() click to toggle source

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

def info?; level <= INFO; end

level=(severity) click to toggle source

Set logging severity threshold.

severity

The Severity of the log message.

def level=(severity) if severity.is_a?(Integer) @level = severity else case severity.to_s.downcase when 'debug' @level = DEBUG when 'info' @level = INFO when 'warn' @level = WARN when 'error' @level = ERROR when 'fatal' @level = FATAL when 'unknown' @level = UNKNOWN else raise ArgumentError, "invalid log level: #{severity}" end end end

log(severity, message = nil, progname = nil) click to toggle source

Alias for: add

Logger#reopen click to toggle source

Logger#reopen(logdev)

Args¶ ↑

logdev

The log device. This is a filename (String) or IO object (typicallySTDOUT, STDERR, or an open file). reopen the same filename if it is nil, do nothing for IO. Default isnil.

Description¶ ↑

Reopen a log device.

def reopen(logdev = nil) @logdev.reopen(logdev) self end

sev_threshold=(severity) click to toggle source

unknown(progname = nil, &block) click to toggle source

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

See info for more information.

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.

def warn(progname = nil, &block) add(WARN, nil, progname, &block) end

warn!() click to toggle source

Sets the severity to WARN.

def warn!; self.level = WARN; end

warn?() click to toggle source

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

def warn?; level <= WARN; end