go-server-flag.go

package main 

import (
    "fmt"
    "log"
    "flag"

    "net/http"
)

var (
    port int
)                                                                                                                                                                                                                                                                                                       

func rootHandler(w http.ResponseWriter, r *http.Request) {
    fmt.Fprint(w, "Hello, World!")
}

func init() {
    flag.IntVar(&port, "port", 8080, "HTTP Server Port")
    flag.Parse()
}

func main() {
    httpAddr := fmt.Sprintf(":%v", port)

    log.Printf("Listening to %v", httpAddr)

    http.HandleFunc("/", rootHandler)
    log.Fatal(http.ListenAndServe(httpAddr, nil))
}