Results for: "Logger"

Logger

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 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.

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 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.

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.

Create a logger which logs messages to STDERR/STDOUT.

logger = Logger.new(STDERR)
logger = Logger.new(STDOUT)

Create a logger for the file which has the specified name.
```
logger = Logger.new('logfile.log')
```

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 = File.open('foo.log', File::WRONLY | File::APPEND | File::CREAT)
logger = Logger.new(file)

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)
```

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.

Message in a block.

logger.fatal { "Argument 'foo' not given." }

Message as a string.

logger.error "Argument #{@foo} mismatch."

With progname.

logger.info('initialize') { "Initializing..." }

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

Original interface.
```
logger.sev_threshold = Logger::WARN
```

Log4r (somewhat) compatible interface.

logger.level = Logger::INFO

# DEBUG < INFO < WARN < ERROR < FATAL < UNKNOWN

Symbol or String (case insensitive)

logger.level = :info
logger.level = 'INFO'

# :debug < :info < :warn < :error < :fatal < :unknown

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'
      # e.g. "2004-01-03 00:54:26"

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
# e.g. "2005-09-22 08:51:08 +0900: hello world"

or via the constructor.

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

Syslog::Logger

Syslog::Logger is a Logger work-alike that logs via syslog instead of to a file. You can use Syslog::Logger to aggregate logs between multiple machines.

By default, Syslog::Logger uses the program name ‘ruby’, but this can be changed via the first argument to Syslog::Logger.new.

NOTE! You can only set the Syslog::Logger program name when you initialize Syslog::Logger for the first time. This is a limitation of the way Syslog::Logger uses syslog (and in some ways, a limitation of the way syslog(3) works). Attempts to change Syslog::Logger‘s program name after the first initialization will be ignored.

Example

The following will log to syslogd on your local machine:

require 'syslog/logger'

log = Syslog::Logger.new 'my_program'
log.info 'this line will be logged via syslog(3)'

Also the facility may be set to specify the facility level which will be used:

log.info 'this line will be logged using Syslog default facility level'

log_local1 = Syslog::Logger.new 'my_program', Syslog::LOG_LOCAL1
log_local1.info 'this line will be logged using local1 facility level'

You may need to perform some syslog.conf setup first. For a BSD machine add the following lines to /etc/syslog.conf:

!my_program
*.*                                             /var/log/my_program.log

Then touch /var/log/my_program.log and signal syslogd with a HUP (killall -HUP syslogd, on FreeBSD).

If you wish to have logs automatically roll over and archive, see the newsyslog.conf(5) and newsyslog(8) man pages.

Logger::LogDevice

Device used for logging messages.

Logger::Formatter

Default formatter for log messages.

Logger::Severity

Logging severity.

Logger::Period

No documentation available

Syslog::Logger::Formatter

Default formatter for log messages.

Logger#log

No documentation available

Logger#error?

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

Logger#error

Log an ERROR message.

See info for more information.

Logger#close

Close the logging device.

Logger#level=

Set logging severity threshold.

severity: The Severity of the log message.

Logger#debug?

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

Logger#info?

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

Logger#warn?

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

Logger#fatal?

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

Logger::new

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). Default value is 0.
shift_size: Maximum logfile size in bytes (only applies when shift_age is a number). 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’.
shift_period_suffix: The log file suffix format for daily, weekly or monthly rotation. Default is ‘%Y%m%d’.

Description

Create an instance.

Logger#reopen

Args

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

Description

Reopen a log device.

Logger#add

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

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.

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.