go templater

templater.go

package main

import (
	"bytes"
	"flag"
	"io"
	"io/ioutil"
	"log"
	"os"
	"strings"
	"text/template"

	"gopkg.in/yaml.v2"
)

var (
	contextFile = flag.String("c", "", "context yaml file")
	dumpCtx     = flag.Bool("d", false, "dump context")
)

func main() {
	flag.Parse()

	log.SetFlags(log.LstdFlags | log.Lshortfile)

	buf := new(bytes.Buffer)
	if _, err := io.Copy(buf, os.Stdin); err != nil {
		log.Fatal(err)
	}

	tmpl, err := template.New("stdin").Parse(buf.String())
	if err != nil {
		log.Fatal(err)
	}

	ctx := make(map[string]interface{})
	if *contextFile != "" {
		ctxbytes, err := slurp(*contextFile)
		if err != nil {
			log.Fatal(err)
		}

		err = yaml.Unmarshal(ctxbytes, &ctx)
		if err != nil {
			log.Fatalf("%s: %v", *contextFile, err)
		}
	}

	env := e2m()
	ctx["env"] = env

	if *dumpCtx {
		for k, v := range ctx {
			log.Printf("%q = %q", k, v)
		}
	}

	err = tmpl.Execute(os.Stdout, ctx)
	if err != nil {
		log.Fatal(err)
	}
}

func slurp(file string) ([]byte, error) {
	f, err := os.Open(file)
	if err != nil {
		return nil, err
	}

	byt, err := ioutil.ReadAll(f)
	if err != nil {
		return nil, err
	}

	return byt, nil
}

func e2m() map[string]string {
	env := os.Environ()
	m := make(map[string]string)
	for _, e := range env {
		spl := strings.SplitN(e, "=", 2)
		m[spl[0]] = spl[1]
	}
	return m
}