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Package log

Overview

Package log implements a simple logging package. It defines a type, Logger, with methods for formatting output. It also has a predefined 'standard' Logger accessible through helper functions Print[f|ln], Fatal[f|ln], and Panic[f|ln], which are easier to use than creating a Logger manually. That logger writes to standard error and prints the date and time of each logged message. Every log message is output on a separate line: if the message being printed does not end in a newline, the logger will add one. The Fatal functions call os.Exit(1) after writing the log message. The Panic functions call panic after writing the log message.

Index

Examples

Logger

Package files

log.go

Constants

These flags define which text to prefix to each log entry generated by the Logger.

const (
        // Bits or'ed together to control what's printed.
        // There is no control over the order they appear (the order listed
        // here) or the format they present (as described in the comments).
        // The prefix is followed by a colon only when Llongfile or Lshortfile
        // is specified.
        // For example, flags Ldate | Ltime (or LstdFlags) produce,
        //	2009/01/23 01:23:23 message
        // while flags Ldate | Ltime | Lmicroseconds | Llongfile produce,
        //	2009/01/23 01:23:23.123123 /a/b/c/d.go:23: message
        Ldate         = 1 << iota     // the date in the local time zone: 2009/01/23
        Ltime                         // the time in the local time zone: 01:23:23
        Lmicroseconds                 // microsecond resolution: 01:23:23.123123.  assumes Ltime.
        Llongfile                     // full file name and line number: /a/b/c/d.go:23
        Lshortfile                    // final file name element and line number: d.go:23. overrides Llongfile
        LUTC                          // if Ldate or Ltime is set, use UTC rather than the local time zone
        LstdFlags     = Ldate | Ltime // initial values for the standard logger
)

func FatalSource

func Fatal(v ...interface{})

Fatal is equivalent to Print() followed by a call to os.Exit(1).

func FatalfSource

func Fatalf(format string, v ...interface{})

Fatalf is equivalent to Printf() followed by a call to os.Exit(1).

func FatallnSource

func Fatalln(v ...interface{})

Fatalln is equivalent to Println() followed by a call to os.Exit(1).

func FlagsSource

func Flags() int

Flags returns the output flags for the standard logger.

func OutputSource

func Output(calldepth int, s string) error

Output writes the output for a logging event. The string s contains the text to print after the prefix specified by the flags of the Logger. A newline is appended if the last character of s is not already a newline. Calldepth is the count of the number of frames to skip when computing the file name and line number if Llongfile or Lshortfile is set; a value of 1 will print the details for the caller of Output.

func PanicSource

func Panic(v ...interface{})

Panic is equivalent to Print() followed by a call to panic().

func PanicfSource

func Panicf(format string, v ...interface{})

Panicf is equivalent to Printf() followed by a call to panic().

func PaniclnSource

func Panicln(v ...interface{})

Panicln is equivalent to Println() followed by a call to panic().

func PrefixSource

func Prefix() string

Prefix returns the output prefix for the standard logger.

func PrintSource

func Print(v ...interface{})

Print calls Output to print to the standard logger. Arguments are handled in the manner of fmt.Print.

func PrintfSource

func Printf(format string, v ...interface{})

Printf calls Output to print to the standard logger. Arguments are handled in the manner of fmt.Printf.

func PrintlnSource

func Println(v ...interface{})

Println calls Output to print to the standard logger. Arguments are handled in the manner of fmt.Println.

func SetFlagsSource

func SetFlags(flag int)

SetFlags sets the output flags for the standard logger.

func SetOutputSource

func SetOutput(w io.Writer)

SetOutput sets the output destination for the standard logger.

func SetPrefixSource

func SetPrefix(prefix string)

SetPrefix sets the output prefix for the standard logger.

type LoggerSource

A Logger represents an active logging object that generates lines of output to an io.Writer. Each logging operation makes a single call to the Writer's Write method. A Logger can be used simultaneously from multiple goroutines; it guarantees to serialize access to the Writer.

type Logger struct {
        // contains filtered or unexported fields
}

Example

package main

import (
	"bytes"
	"fmt"
	"log"
)

func main() {
	var buf bytes.Buffer
	logger := log.New(&buf, "logger: ", log.Lshortfile)
	logger.Print("Hello, log file!")

	fmt.Print(&buf)
}

func NewSource

func New(out io.Writer, prefix string, flag int) *Logger

New creates a new Logger. The out variable sets the destination to which log data will be written. The prefix appears at the beginning of each generated log line. The flag argument defines the logging properties.

func (*Logger) FatalSource

func (l *Logger) Fatal(v ...interface{})

Fatal is equivalent to l.Print() followed by a call to os.Exit(1).

func (*Logger) FatalfSource

func (l *Logger) Fatalf(format string, v ...interface{})

Fatalf is equivalent to l.Printf() followed by a call to os.Exit(1).

func (*Logger) FatallnSource

func (l *Logger) Fatalln(v ...interface{})

Fatalln is equivalent to l.Println() followed by a call to os.Exit(1).

func (*Logger) FlagsSource

func (l *Logger) Flags() int

Flags returns the output flags for the logger.

func (*Logger) OutputSource

func (l *Logger) Output(calldepth int, s string) error

Output writes the output for a logging event. The string s contains the text to print after the prefix specified by the flags of the Logger. A newline is appended if the last character of s is not already a newline. Calldepth is used to recover the PC and is provided for generality, although at the moment on all pre-defined paths it will be 2.

func (*Logger) PanicSource

func (l *Logger) Panic(v ...interface{})

Panic is equivalent to l.Print() followed by a call to panic().

func (*Logger) PanicfSource

func (l *Logger) Panicf(format string, v ...interface{})

Panicf is equivalent to l.Printf() followed by a call to panic().

func (*Logger) PaniclnSource

func (l *Logger) Panicln(v ...interface{})

Panicln is equivalent to l.Println() followed by a call to panic().

func (*Logger) PrefixSource

func (l *Logger) Prefix() string

Prefix returns the output prefix for the logger.

func (*Logger) PrintSource

func (l *Logger) Print(v ...interface{})

Print calls l.Output to print to the logger. Arguments are handled in the manner of fmt.Print.

func (*Logger) PrintfSource

func (l *Logger) Printf(format string, v ...interface{})

Printf calls l.Output to print to the logger. Arguments are handled in the manner of fmt.Printf.

func (*Logger) PrintlnSource

func (l *Logger) Println(v ...interface{})

Println calls l.Output to print to the logger. Arguments are handled in the manner of fmt.Println.

func (*Logger) SetFlagsSource

func (l *Logger) SetFlags(flag int)

SetFlags sets the output flags for the logger.

func (*Logger) SetOutputSource

func (l *Logger) SetOutput(w io.Writer)

SetOutput sets the output destination for the logger.

func (*Logger) SetPrefixSource

func (l *Logger) SetPrefix(prefix string)

SetPrefix sets the output prefix for the logger.

Subdirectories

Name Synopsis
..
syslog Package syslog provides a simple interface to the system log service.

© Google, Inc.
Licensed under the Creative Commons Attribution License 3.0.
https://golang.org/pkg/log/