CODEWITHSUNDEEP
gologging
topskip
topskip

Reputation: 17335

How to change the date/time format of Go's log package

When using the log package, Go outputs something like 

2009/11/10 23:00:00 Hello, world

How can I change the date and time format to something like dd.mm.yyy hh:mm:ss? Example (playground link):

package main

import "log"

func main() {
    log.Println("Hello, playground")
}

Upvotes: 39

Views: 30574

Answers (4)

danysz
danysz

Reputation: 628

It's much easier to use the flags from Logger system internal.

    log.SetFlags(log.Lmicroseconds)

Use this flag to add timestamp with microseconds to the log. Other available options are : 

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

)

Golang logger documentation is available here

Upvotes: 1

clangager
clangager

Reputation: 1013

Like yed posterior said, you can define a custom io.Writer by implementing a write function. You'll also probably want to do a log.SetFlags(0) to take full control. Here's an example that changes the date format as well as adds some log level info.

type logWriter struct {
}

func (writer logWriter) Write(bytes []byte) (int, error) {
    return fmt.Print(time.Now().UTC().Format("2006-01-02T15:04:05.999Z") + " [DEBUG] " + string(bytes))
}

func main() {

    log.SetFlags(0)
    log.SetOutput(new(logWriter))
    log.Println("This is something being logged!")
}

outputs:

2016-03-21T19:54:28.563Z [DEBUG] This is something being logged!

Upvotes: 71

Teoman Soygul
Teoman Soygul

Reputation: 25732

According to the source (http://golang.org/src/pkg/log/log.go) there is no built-in way to do that:

26      // Bits or'ed together to control what's printed. There is no control over the
27      // order they appear (the order listed here) or the format they present (as
28      // described in the comments).  A colon appears after these items:
29      //  2009/01/23 01:23:23.123123 /a/b/c/d.go:23: message

You'll need to use a 3rd party package for that, or intercept the log output as yed described.

Upvotes: 6

yed posterior
yed posterior

Reputation: 51

Use a custom writer that filters the log lines to modify them to the format you need. It should be easy because the format of the header is regular and fixed-width. Then call log.SetOutput(myFilterWriter(os.Stderr)).

Upvotes: 5

Related Questions