init_port.go

package main

import "flag"
import "os"
import "strconv"
import "fmt"

var port *int

func init() {
	defaultPort, err := strconv.Atoi(os.Getenv("PORT"))
	if err != nil {
		defaultPort = 8080
	}

	port = flag.Int("port", defaultPort, "port number")
}

func main() {
	flag.Parse()

	fmt.Printf("port: %d\n", *port)
}

port.go

package main

import "flag"
import "os"
import "strconv"
import "fmt"

var port = flag.Int("port", 0, "port number")

func main() {
	flag.Parse()

	if *port == 0 {
		envPort, err := strconv.Atoi(os.Getenv("PORT"))
		if err != nil {
			*port = 8080
		} else {
			*port = envPort
		}
	}

	fmt.Printf("port: %d\n", *port)
}