pattern := flag.String("pattern", "%{GREEDYDATA:msg}", "a grok expression")

namedcapture := flag.Bool("namedcapture", false, "parse only named captures (default is false)")

flag.Parse()

var g *grok.Grok

if *namedcapture {

g = grok.NewWithConfig(&grok.Config{NamedCapturesOnly: true})

} else {

g = grok.New()

}

scanner := bufio.NewScanner(os.Stdin)

for scanner.Scan() {

line := scanner.Text()

values, _ := g.Parse(*pattern, line)

delete(values, "")

encoded, _ := json.Marshal(values)

fmt.Println(string(encoded))

}