log

README

This repository contains logging packages for Go:

• stdlog is the main package of this repository, it is a simple and fast logger to the standard output.
• buflog and golog are customizable logging class which can be used as a standalone or as a building block for other loggers. stdlog is built upon them.
• log just provides a common interface for logging libraries.

You are more than welcome to ask questions on the Go mailing-list and open issues here if you find bugs.

stdlog

Documentation

Package stdlog provides simple and fast logging to the standard output (stdout) and is optimized for programs launched via a shell or cron. It can also be used to log to a file by redirecting the standard output to a file. This package is thread-safe.

Basic examples:

logger := stdlog.GetFromFlags()
logger.Info("Connecting to the server...")
logger.Errorf("Connection failed: %q", err)

Will output:

2014-04-02 18:09:15.862 INFO Connecting to the API...
2014-04-02 18:10:14.347 ERROR Connection failed (Server is unavailable).

Log*() functions can be used to avoid evaluating arguments when it is expensive and unnecessary:

logger.Debug("Memory usage: %s", getMemoryUsage())
if LogDebug() { logger.Debug("Memory usage: %s", getMemoryUsage()) }

If debug logging is off the getMemoryUsage() will be executed on the first line while it will not be executed on the second line.

List of command-line arguments:

-log=info
    Log events at or above this level are logged.
-stderr=false
    Logs are written to standard error (stderr) instead of standard
    output.
-flushlog=none
    Until this level is reached nothing is output and logs are stored
    in the memory. Once a log event is at or above this level, it
    outputs all logs in memory as well as the future log events. This
    feature should not be used with long-running processes.

The available levels are the eight ones described in RFC 5424 (debug, info, notice, warning, error, critical, alert, emergency) and none.

Some use cases:

• By default, all logs except debug ones are output to the stdout. Which is useful to follow the execution of a program launched via a shell.
• A program launched by a crontab where the variable MAILTO is set with -debug -flushlog=error will send all logs generated by the program only if an error happens. When there is no error the email will not be sent.
• my_program > /var/log/my_program/my_program-$(date+%Y-%m-%d-%H%M%S).log will create a log file in /var/log/my_program each time it is run.

buflog

Documentation

Package buflog provides a buffered logging class that accumulates logs in memory until the flush threshold is reached which release stored logs, the buffered logger then act as a normal logger.

Basic example:

logger := buflog.New(os.Stdout, log.Info, log.Error)
logger.Info("Connecting to the server...")   // Outputs nothing
logger.Error("Connection failed")            // Outputs both lines

golog

Documentation

Package golog provides a customizable logging class which can be used as a standalone or as a building block for other loggers.

Basic example:

logger := golog.New(os.Stdout, log.Info)
logger.Info("Connecting to the server...")
logger.Errorf("Connection failed: %q", err)

Will output:

2014-04-02 18:09:15.862 INFO Connecting to the API...
2014-04-02 18:10:14.347 ERROR Connection failed (Server is unavailable).

Log*() functions can be used to avoid evaluating arguments when it is expensive and unnecessary:

logger.Debug("Memory usage: %s", getMemoryUsage())
if logger.LogDebug() { logger.Debug("Memory usage: %s", getMemoryUsage()) }

If debug logging is off getMemoryUsage() will be executed on the first line while it will not be executed on the second line.

log

Documentation

Package log provides a common interface for logging libraries.

Documentation

Overview

Package log provides a common interface for logging libraries.

Index

• Variables
• type Level
• type Logger

Variables

var NullLogger = nullLogger{}

NullLogger is a no-op instance of the Logger interface.

Types

type Level

type Level int8

Level specifies a level of verbosity. The available levels are the eight severities described in RFC 5424 and none.

const (
	None Level = iota - 1
	Emergency
	Alert
	Critical
	Error
	Warning
	Notice
	Info
	Debug
)

type Logger

type Logger interface {
	// Emergency logs with an emergency level.
	Emergency(args ...interface{})

	// Emergencyf logs with an emergency level.
	// Arguments are handled in the manner of fmt.Printf.
	Emergencyf(format string, args ...interface{})

	// Alert logs with an alert level.
	Alert(args ...interface{})

	// Alertf logs with an alert level.
	// Arguments are handled in the manner of fmt.Printf.
	Alertf(format string, args ...interface{})

	// Critical logs with a critical level.
	Critical(args ...interface{})

	// Criticalf logs with a critical level.
	// Arguments are handled in the manner of fmt.Printf.
	Criticalf(format string, args ...interface{})

	// Error logs with an error level.
	Error(args ...interface{})

	// Errorf logs with an error level.
	// Arguments are handled in the manner of fmt.Printf.
	Errorf(format string, args ...interface{})

	// Warning logs with a warning level.
	Warning(args ...interface{})

	// Warningf logs with a warning level.
	// Arguments are handled in the manner of fmt.Printf.
	Warningf(format string, args ...interface{})

	// Notice logs with a notice level.
	Notice(args ...interface{})

	// Noticef logs with a notice level.
	// Arguments are handled in the manner of fmt.Printf.
	Noticef(format string, args ...interface{})

	// Info logs with an info level.
	Info(args ...interface{})

	// Infof logs with an info level.
	// Arguments are handled in the manner of fmt.Printf.
	Infof(format string, args ...interface{})

	// Debug logs with a debug level.
	Debug(args ...interface{})

	// Debugf logs with a debug level.
	// Arguments are handled in the manner of fmt.Printf.
	Debugf(format string, args ...interface{})

	// Log logs at the level passed in argument.
	Log(level Level, args ...interface{})

	// Logf logs at the level passed in argument.
	// Arguments are handled in the manner of fmt.Printf.
	Logf(level Level, format string, args ...interface{})

	// LogEmergency returns true if the log level is at emergency or lower.
	LogEmergency() bool

	// LogAlert returns true if the log level is at alert or lower.
	LogAlert() bool

	// LogCritical returns true if the log level is at critical or lower.
	LogCritical() bool

	// LogError returns true if the log level is at error or lower.
	LogError() bool

	// LogWarning returns true if the log level is at warning or lower.
	LogWarning() bool

	// LogNotice returns true if the log level is at notice or lower.
	LogNotice() bool

	// LogInfo returns true if the log level is at info or debug.
	LogInfo() bool

	// LogDebug returns true only if the log level is at debug.
	LogDebug() bool

	// LogLevel returns true if the log level is at or below the level argument.
	LogLevel(level Level) bool

	io.Closer
}

Logger is a common interface for logging libraries.