funcs: Add exec

dir.go

@@ -114,7 +114,9 @@ func (d *Dir) _read(srcDir, path string, task *Task, cfg *Site) error {
 			}
 
 			if cmd, ok := task.Preprocess[strings.TrimPrefix(ext, ".")]; ok {
-				content = process(cmd, bytes.NewReader(content))
+				var buf bytes.Buffer
+				execute(cmd, bytes.NewReader(content), &buf)
+				content = buf.Bytes()
 			}
 			page.Content = string(content)
 
@@ -228,7 +230,9 @@ func (d *Dir) write(dstDir string, task *Task) error {
 		}
 		var content []byte
 		if cmd := task.Postprocess; cmd != "" {
-			content = process(cmd, strings.NewReader(page.Content))
+			var buf bytes.Buffer
+			execute(cmd, strings.NewReader(page.Content), &buf)
+			content = buf.Bytes()
 		} else {
 			content = []byte(page.Content)
 		}
@@ -290,17 +294,17 @@ func (d *Dir) sort() {
 	}
 }
 
-// process runs a process command.
-func process(command string, input io.Reader) []byte {
+// execute runs a command.
+func execute(command string, input io.Reader, output io.Writer) {
 	split := strings.Split(command, " ")
 	cmd := exec.Command(split[0], split[1:]...)
 	cmd.Stdin = input
 	cmd.Stderr = os.Stderr
-	output, err := cmd.Output()
+	cmd.Stdout = output
+	err := cmd.Run()
 	if err != nil {
 		log.Fatal(err)
 	}
-	return output
 }
 
 func (d *Dir) Title() string {

funcs.go

@@ -11,6 +11,7 @@ import (
 func (s *Site) funcs() map[string]interface{} {
 	return map[string]interface{}{
 		"dir":          s.dir,
+		"exec":         executeString,
 		"page":         s.page,
 		"path":         func() _path { return _path{} },
 		"partial":      s.templates.ExecutePartial,
@@ -54,6 +55,12 @@ func (_strings) TrimRight(a, b string) string         { return strings.TrimRight
 func (_strings) TrimSpace(s string) string            { return strings.TrimSpace(s) }
 func (_strings) TrimSuffix(a, b string) string        { return strings.TrimSuffix(a, b) }
 
+func executeString(command, input string) string {
+	var b strings.Builder
+	execute(command, strings.NewReader(input), &b)
+	return b.String()
+}
+
 func reverse(s interface{}) interface{} {
 	v := reflect.ValueOf(s)
 	n := v.Len()