read-env-runtime.go

package main

import (
	"fmt"
	"log"
	"net/http"
	"os"
)

func handler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintln(w, "Hello, 世界")
}

func main() {
	var port = os.Getenv("PORT")
	fmt.Println(port)

	http.HandleFunc("/", handler)
	fmt.Println("Running demo app. Press Ctrl+C to exit...")
	log.Fatal(http.ListenAndServe(":"+port, nil))
}

read-file-runtime.go

package main

import (
	"fmt"
	"log"
	"net/http"
	"os"
)

func handler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintln(w, "Hello, 世界")
}

func main() {
	var jsonFile, err = os.Open("config.json")
	if err != nil {
	  	log.Fatal(err)
	}
	fmt.Println(jsonFile)

	http.HandleFunc("/", handler)
	fmt.Println("Running demo app. Press Ctrl+C to exit...")
	log.Fatal(http.ListenAndServe(":8080", nil))
}