packer: ParseTemplateFile understands "-" to mean stdin

packer/template.go

 package packer
 
 import (
+	"bytes"
 	"fmt"
 	"github.com/mitchellh/mapstructure"
 	jsonutil "github.com/mitchellh/packer/common/json"
+	"io"
 	"io/ioutil"
+	"os"
 	"sort"
 )
 
@@ -235,9 +238,23 @@ func ParseTemplate(data []byte) (t *Template, err error) {
 // ParseTemplateFile takes the given template file and parses it into
 // a single template.
 func ParseTemplateFile(path string) (*Template, error) {
-	data, err := ioutil.ReadFile(path)
-	if err != nil {
-		return nil, err
+	var data []byte
+
+	if path == "-" {
+		// Read from stdin...
+		buf := new(bytes.Buffer)
+		_, err := io.Copy(buf, os.Stdin)
+		if err != nil {
+			return nil, err
+		}
+
+		data = buf.Bytes()
+	} else {
+		var err error
+		data, err = ioutil.ReadFile(path)
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	return ParseTemplate(data)

packer/template_test.go

@@ -3,6 +3,7 @@ package packer
 import (
 	"cgl.tideland.biz/asserts"
 	"io/ioutil"
+	"os"
 	"reflect"
 	"sort"
 	"testing"
@@ -43,6 +44,39 @@ func TestParseTemplateFile_basic(t *testing.T) {
 	}
 }
 
+func TestParseTemplateFile_stdin(t *testing.T) {
+	data := `
+	{
+		"builders": [{"type": "something"}]
+	}
+	`
+
+	tf, err := ioutil.TempFile("", "packer")
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	defer tf.Close()
+	tf.Write([]byte(data))
+
+	// Sync and seek to the beginning so that we can re-read the contents
+	tf.Sync()
+	tf.Seek(0, 0)
+
+	// Set stdin to something we control
+	oldStdin := os.Stdin
+	defer func() { os.Stdin = oldStdin }()
+	os.Stdin = tf
+
+	result, err := ParseTemplateFile("-")
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if len(result.Builders) != 1 {
+		t.Fatalf("bad: %#v", result.Builders)
+	}
+}
+
 func TestParseTemplate_Basic(t *testing.T) {
 	assert := asserts.NewTestingAsserts(t, true)