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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. The Fatal functions call os.Exit(1) after writing the log message. The Panic functions call panic after writing the log message.

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 Fatal

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

func Fatal(v ...interface{})

func Fatalf

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

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

func Fatalln

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

func Fatalln(v ...interface{})

func Flags

Flags returns the output flags for the standard logger.

func Flags() int

func Output

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 Output(calldepth int, s string) error

func Panic

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

func Panic(v ...interface{})

func Panicf

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

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

func Panicln

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

func Panicln(v ...interface{})

func Prefix

Prefix returns the output prefix for the standard logger.

func Prefix() string

func Print

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

func Print(v ...interface{})

func Printf

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

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

func Println

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

func Println(v ...interface{})

func SetFlags

SetFlags sets the output flags for the standard logger.

func SetFlags(flag int)

func SetOutput

SetOutput sets the output destination for the standard logger.

func SetOutput(w io.Writer)

func SetPrefix

SetPrefix sets the output prefix for the standard logger.

func SetPrefix(prefix string)

type Logger

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

logger: example_test.go:16: Hello, log file!

func New

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

func (*Logger) Fatal

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

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

func (*Logger) Fatalf

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

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

func (*Logger) Fatalln

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

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

func (*Logger) Flags

Flags returns the output flags for the logger.

func (l *Logger) Flags() int

func (*Logger) Output

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

func (*Logger) Panic

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

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

func (*Logger) Panicf

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

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

func (*Logger) Panicln

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

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

func (*Logger) Prefix

Prefix returns the output prefix for the logger.

func (l *Logger) Prefix() string

func (*Logger) Print

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

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

func (*Logger) Printf

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

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

func (*Logger) Println

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

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

func (*Logger) SetFlags

SetFlags sets the output flags for the logger.

func (l *Logger) SetFlags(flag int)

func (*Logger) SetOutput

SetOutput sets the output destination for the logger.

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

func (*Logger) SetPrefix

SetPrefix sets the output prefix for the logger.

func (l *Logger) SetPrefix(prefix string)

Subdirectories

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