Documentation

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

    Constants

    View Source
    const (
    	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
    	Lmsgprefix                    // move the "prefix" from the beginning of the line to before the message
    	LstdFlags     = Ldate | Ltime // initial values for the standard logger
    )

      These flags define which text to prefix to each log entry generated by the Logger. Bits are or'ed together to control what's printed. With the exception of the Lmsgprefix flag, 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
      

      Variables

      This section is empty.

      Functions

      func Fatal

      func Fatal(v ...interface{})

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

        func Fatalf

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

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

          func Fatalln

          func Fatalln(v ...interface{})

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

            func Flags

            func Flags() int

              Flags returns the output flags for the standard logger. The flag bits are Ldate, Ltime, and so on.

              func Output added in go1.5

              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 Panic

                func Panic(v ...interface{})

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

                  func Panicf

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

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

                    func Panicln

                    func Panicln(v ...interface{})

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

                      func Prefix

                      func Prefix() string

                        Prefix returns the output prefix for the standard logger.

                        func Print

                        func Print(v ...interface{})

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

                          func Printf

                          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 Println

                            func Println(v ...interface{})

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

                              func SetFlags

                              func SetFlags(flag int)

                                SetFlags sets the output flags for the standard logger. The flag bits are Ldate, Ltime, and so on.

                                func SetOutput

                                func SetOutput(w io.Writer)

                                  SetOutput sets the output destination for the standard logger.

                                  func SetPrefix

                                  func SetPrefix(prefix string)

                                    SetPrefix sets the output prefix for the standard logger.

                                    func Writer added in go1.13

                                    func Writer() io.Writer

                                      Writer returns the output destination for the standard logger.

                                      Types

                                      type Logger

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

                                        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.

                                        Example
                                        Output:
                                        
                                        logger: example_test.go:19: Hello, log file!
                                        

                                        func Default added in go1.16

                                        func Default() *Logger

                                          Default returns the standard logger used by the package-level output functions.

                                          func New

                                          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, or after the log header if the Lmsgprefix flag is provided. The flag argument defines the logging properties.

                                            func (*Logger) Fatal

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

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

                                              func (*Logger) Fatalf

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

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

                                                func (*Logger) Fatalln

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

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

                                                  func (*Logger) Flags

                                                  func (l *Logger) Flags() int

                                                    Flags returns the output flags for the logger. The flag bits are Ldate, Ltime, and so on.

                                                    func (*Logger) Output

                                                    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.

                                                      Example
                                                      Output:
                                                      
                                                      INFO: example_test.go:36: Hello world
                                                      

                                                      func (*Logger) Panic

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

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

                                                        func (*Logger) Panicf

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

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

                                                          func (*Logger) Panicln

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

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

                                                            func (*Logger) Prefix

                                                            func (l *Logger) Prefix() string

                                                              Prefix returns the output prefix for the logger.

                                                              func (*Logger) Print

                                                              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) Printf

                                                                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) Println

                                                                  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) SetFlags

                                                                    func (l *Logger) SetFlags(flag int)

                                                                      SetFlags sets the output flags for the logger. The flag bits are Ldate, Ltime, and so on.

                                                                      func (*Logger) SetOutput added in go1.5

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

                                                                        SetOutput sets the output destination for the logger.

                                                                        func (*Logger) SetPrefix

                                                                        func (l *Logger) SetPrefix(prefix string)

                                                                          SetPrefix sets the output prefix for the logger.

                                                                          func (*Logger) Writer added in go1.12

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

                                                                            Writer returns the output destination for the logger.

                                                                            Source Files

                                                                            Directories

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