foo.go

package main

import (
	"github.com/golang/glog"
)

func foo() {
	glog.Info("info v1")
	glog.Error("error v1")

	glog.V(2).Info("info v2")
}

main.go

package main

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

func main() {
	flag.Parse()

	glog.Info("info v1")
	glog.Error("error v1")

	if glog.V(2) {
		glog.Info("info v2")
		glog.Error("error v2")
	}

	glog.V(3).Info("info v3")
	if glog.V(3) {
		glog.Error("error v3")
	}

	foo()
}

memo.md

--help

$ ./glog --help
Usage of ./glog:
  -alsologtostderr=false: log to standard error as well as files
  -log_backtrace_at=:0: when logging hits line file:N, emit a stack trace
  -log_dir="": If non-empty, write log files in this directory
  -logtostderr=false: log to standard error instead of files
  -stderrthreshold=0: logs at or above this threshold go to stderr
  -v=0: log level for V logs
  -vmodule=: comma-separated list of pattern=N settings for file-filtered logging

-logtostderr

$ ./glog -logtostderr
I0720 11:05:38.503918 25749 main.go:12] info v1
E0720 11:05:38.504035 25749 main.go:13] error v1
I0720 11:05:38.504043 25749 foo.go:8] info v1
E0720 11:05:38.504049 25749 foo.go:9] error v1

-vmodule=foo=2

$ ./glog -logtostderr -vmodule=foo=2
I0720 11:07:04.466255 25795 main.go:12] info v1
E0720 11:07:04.466354 25795 main.go:13] error v1
I0720 11:07:04.466366 25795 foo.go:8] info v1
E0720 11:07:04.466372 25795 foo.go:9] error v1
I0720 11:07:04.466378 25795 foo.go:11] info v2

-log_dir="."

$ ./glog -log_dir="."
E0720 13:41:21.245751 26875 main.go:12] error v1
E0720 13:41:21.246226 26875 foo.go:9] error v1
$ ls
glog
glog.Mac.atotto.log.ERROR.20130720-134121.26875
glog.Mac.atotto.log.INFO.20130720-134121.26875
glog.Mac.atotto.log.WARNING.20130720-134121.26875
glog.ERROR
glog.INFO
glog.WARNING
foo.go
main.go

example for glog.

glog : https://github.com/golang/glog
my blog : http://atotto.hatenadiary.jp/entry/2013/07/20/154439 (Japanese)