class

Logger

Inherits Reference / Object

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 or ERROR that indicate their importance. You can then give the Logger a level, and only messages at that level or higher will be printed.

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

Example

require "logger"

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

# or
log = Logger.new(STDOUT, level: Logger::WARN)

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

begin
  File.each_line("/foo/bar.log") 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

If logging to multiple locations is required, an IO::MultiWriter can be used.

file = File.new("production.log", "a")
writer = IO::MultiWriter.new(file, STDOUT)

log = Logger.new(writer)
log.level = Logger::DEBUG
log.debug("Created logger")

Constants

DEBUG = Severity::DEBUG

ERROR = Severity::ERROR

FATAL = Severity::FATAL

INFO = Severity::INFO

UNKNOWN = Severity::UNKNOWN

VERSION = "0.1.0"

WARN = Severity::WARN

Constructors

new(io : IO | Nil, level : Logger::Severity = Severity::INFO, formatter : Logger::Severity, Time, String, String, IO -> _ = DEFAULT_FORMATTER, progname : String = "")

Creates a new logger that will log to the given io. If io is nil then all log calls will be silently ignored.

Instance methods

close

Calls the close method on the object passed to initialize.

debug(message, progname = nil)

Logs message if the logger's current severity is lower or equal to DEBUG. progname overrides a default progname set in this logger.

debug(progname = nil, &)

Logs the message as returned from the given block if the logger's current severity is lower or equal to DEBUG. The block is not run if the severity is higher. progname overrides a default progname set in this logger.

debug?

Returns true if the logger's current severity is lower or equal to DEBUG.

error(message, progname = nil)

Logs message if the logger's current severity is lower or equal to ERROR. progname overrides a default progname set in this logger.

error(progname = nil, &)

Logs the message as returned from the given block if the logger's current severity is lower or equal to ERROR. The block is not run if the severity is higher. progname overrides a default progname set in this logger.

error?

Returns true if the logger's current severity is lower or equal to ERROR.

fatal(message, progname = nil)

Logs message if the logger's current severity is lower or equal to FATAL. progname overrides a default progname set in this logger.

fatal(progname = nil, &)

Logs the message as returned from the given block if the logger's current severity is lower or equal to FATAL. The block is not run if the severity is higher. progname overrides a default progname set in this logger.

fatal?

Returns true if the logger's current severity is lower or equal to FATAL.

formatter

Customizable Proc (with a reasonable default) which the Logger uses to format and print its entries.

Use this setter to provide a custom formatter. The Logger will invoke it with the following arguments:

severity: a Logger::Severity
datetime: Time, the entry's timestamp
progname: String, the program name, if set when the logger was built
message: String, the body of a message
io: IO, the Logger's stream, to which you must write the final output

Example:

require "logger"

logger = Logger.new(STDOUT)
logger.progname = "YodaBot"

logger.formatter = Logger::Formatter.new do |severity, datetime, progname, message, io|
  label = severity.unknown? ? "ANY" : severity.to_s
  io << label[0] << ", [" << datetime << " #" << Process.pid << "] "
  io << label.rjust(5) << " -- " << progname << ": " << message
end

logger.warn("Fear leads to anger. Anger leads to hate. Hate leads to suffering.")

# Prints to the console:
# "W, [2017-05-06 18:00:41 -0300 #11927]  WARN --
#  YodaBot: Fear leads to anger. Anger leads to hate. Hate leads to suffering."

formatter=(formatter : Logger::Severity, Time, String, String, IO -> _)

Customizable Proc (with a reasonable default) which the Logger uses to format and print its entries.

Use this setter to provide a custom formatter. The Logger will invoke it with the following arguments:

severity: a Logger::Severity
datetime: Time, the entry's timestamp
progname: String, the program name, if set when the logger was built
message: String, the body of a message
io: IO, the Logger's stream, to which you must write the final output

Example:

require "logger"

logger = Logger.new(STDOUT)
logger.progname = "YodaBot"

logger.formatter = Logger::Formatter.new do |severity, datetime, progname, message, io|
  label = severity.unknown? ? "ANY" : severity.to_s
  io << label[0] << ", [" << datetime << " #" << Process.pid << "] "
  io << label.rjust(5) << " -- " << progname << ": " << message
end

logger.warn("Fear leads to anger. Anger leads to hate. Hate leads to suffering.")

# Prints to the console:
# "W, [2017-05-06 18:00:41 -0300 #11927]  WARN --
#  YodaBot: Fear leads to anger. Anger leads to hate. Hate leads to suffering."

info(message, progname = nil)

Logs message if the logger's current severity is lower or equal to INFO. progname overrides a default progname set in this logger.

info(progname = nil, &)

Logs the message as returned from the given block if the logger's current severity is lower or equal to INFO. The block is not run if the severity is higher. progname overrides a default progname set in this logger.

info?

Returns true if the logger's current severity is lower or equal to INFO.

level

level=(level : Severity)

log(severity, message, progname = nil)

Logs message if severity is higher or equal with the logger's current severity. progname overrides a default progname set in this logger.

log(severity, progname = nil, &)

Logs the message as returned from the given block if severity is higher or equal with the loggers current severity. The block is not run if severity is lower. progname overrides a default progname set in this logger.

progname

progname=(progname : String)

unknown(message, progname = nil)

Logs message if the logger's current severity is lower or equal to UNKNOWN. progname overrides a default progname set in this logger.

unknown(progname = nil, &)

Logs the message as returned from the given block if the logger's current severity is lower or equal to UNKNOWN. The block is not run if the severity is higher. progname overrides a default progname set in this logger.

unknown?

Returns true if the logger's current severity is lower or equal to UNKNOWN.

warn(message, progname = nil)

Logs message if the logger's current severity is lower or equal to WARN. progname overrides a default progname set in this logger.

warn(progname = nil, &)

Logs the message as returned from the given block if the logger's current severity is lower or equal to WARN. The block is not run if the severity is higher. progname overrides a default progname set in this logger.

warn?

Returns true if the logger's current severity is lower or equal to WARN.

Nested types