/index.html

## index.html
<p>Hello</p>

## layout.html
<!DOCTYPE html>
<html>
  <head>
  </head>
  <body>
    <div id="content">
      {{template "content" .}}
    </div>
  </body>
</html>

## main.go
package main

import (
	"log"
	"net/http"
	"text/template"
)

var (
	layout = template.Must(template.ParseFiles("layout.html"))
	index  = parsePartial(layout, "index.html")
)

// parsePartial parses a partial template file and adds it as a template named 'content'
// to a clone of the layout template.
func parseTemplate(layout *template.Template, name string) *template.Template {
	t := template.Must(template.ParseFiles(name))
	l := template.Must(layout.Clone())
	return template.Must(l.AddParseTree("content", t.Tree))
}

// MainHandler is an example handler
func MainHandler(w http.ResponseWriter, r *http.Request) {
	if err := index.Execute(w, nil); err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}
}

func main() {
	http.HandleFunc("/", MainHandler)
	log.Fatal(http.ListenAndServe(":8080", nil))
}

## output.html
<!DOCTYPE html>
<html>
  <head>
  </head>
  <body>
    <div id="content">
      <p>Hello</p>
    </div>
  </body>
</html>
	<!DOCTYPE html>
	<html>
	<head>
	</head>
	<body>
	<div id="content">
	{{template "content" .}}
	</div>
	</body>
	</html>
	package main

	import (
	"log"
	"net/http"
	"text/template"
	)

	var (
	layout = template.Must(template.ParseFiles("layout.html"))
	index = parsePartial(layout, "index.html")
	)

	// parsePartial parses a partial template file and adds it as a template named 'content'
	// to a clone of the layout template.
	func parseTemplate(layout template.Template, name string) template.Template {
	t := template.Must(template.ParseFiles(name))
	l := template.Must(layout.Clone())
	return template.Must(l.AddParseTree("content", t.Tree))
	}

	// MainHandler is an example handler
	func MainHandler(w http.ResponseWriter, r *http.Request) {
	if err := index.Execute(w, nil); err != nil {
	http.Error(w, err.Error(), http.StatusInternalServerError)
	}
	}

	func main() {
	http.HandleFunc("/", MainHandler)
	log.Fatal(http.ListenAndServe(":8080", nil))
	}