put a json structure on stdin, call `template-apply path/to/template`, receive executed template on stdout

template-apply.go

package main

import (
	"encoding/json"
	"io/ioutil"
	"os"
	"text/template"
)

func check(err error) {
	if err != nil {
		panic(err)
	}
}

func main() {
	var f interface{}

	b, err := ioutil.ReadAll(os.Stdin)
	check(err)

	check(json.Unmarshal(b, &f))

	check(template.Must(template.ParseFiles(os.Args[1])).Execute(os.Stdout, f))
}