An example of how to use golang/glog.

glog-example.go

/*
glog-example
------------

background
---
You probably want to read the source code comments at the top of the glog.go file in 
the golang/glog repository on github.com. Located here: https://github.com/golang/glog/blob/master/glog.go

setup
---

	$ go get github.com/golang/glog
	$ mkdir log

run 
---

	$ go run example.go -stderrthreshold=FATAL -log_dir=./log
or

	$ go run example.go -stderrthreshold=FATAL -log_dir=./log -v=2
or

	$ go run example.go -logtostderr=true
or

	$ go run example.go -logtostderr=true -v=2

*/

package main

import (
	"github.com/golang/glog"
	"os"
	"flag"
	"fmt"
)

func usage() {
	fmt.Fprintf(os.Stderr, "usage: example -stderrthreshold=[INFO|WARNING|FATAL] -log_dir=[string]\n", )
	flag.PrintDefaults()
	os.Exit(2)
}

func init() {
	flag.Usage = usage
	// NOTE: This next line is key you have to call flag.Parse() for the command line 
	// options or "flags" that are defined in the glog module to be picked up.
	flag.Parse()
}

func main() {
	number_of_lines := 100000
	for i := 0; i < number_of_lines; i++ {
		glog.V(2).Infof("LINE: %d", i)
		message := fmt.Sprintf("TEST LINE: %d", i)
		glog.Error(message)
	}
	glog.Flush()
}

You need to add a call to glog.Flush() here to guarantee that all output makes it to the log file.

Thanks!

glog.Flush() hint is a lifesaver.

it's useful,thanks!

-stderrthreshold=[INFO|WARN|FATAL]

are you sure there is WARN,rather than WARNING?

-stderrthreshold=[INFO|WARN|FATAL]

are you sure there is WARN,rather than WARNING?

Thank you. It's definitely WARNING.

it's useful,thanks!

You are very welcome!

So what happens if i abort (cntrl-c) before the glog.flush() is issued? is it just not guaranteed but possible to be written to file?

So what happens if i abort (cntrl-c) before the glog.flush() is issued? is it just not guaranteed but possible to be written to file?

Your code that consumes glog should handle SIGINT (ctrl-c), and do one last glog.Flush()!

May I ask you a question? When the log file is too large, could it be rotated automatically?

May I ask you a question? When the log file is too large, could it be rotated automatically?

Yes rotated automatically.

Thanks! Question: does golang/glog also support supplying the options via environment variables instead of command line flags? In https://github.com/google/glog#user-guide it says we can do

GLOG_logtostderr=1 ./your_application

is that possible in the go version?

I browsed the source located here: https://github.com/golang/glog

It appears there is no support for environment variables in this implementation. :(