Parse command line argument by Go

flag.go

package main

import (
    "flag"
    "fmt"
    "time"
)

var (
    message = flag.String("message", "Hello!", "What to say")
    delay   = flag.Duration("delay", 2*time.Second, "How long to wait")
)

func main() {
    flag.Parse()
    fmt.Println(*message)
    time.Sleep(*delay)
    fmt.Println("Done")
}

test.sh

go run flag.go --help
go run flag.go
go run flag.go -message "Hello world"
go run flag.go -message "Hello world" -delay 5m