Map postprocess command stderr to os.Stderr

config.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"bytes"
 	"log"
 	"os"
 	"os/exec"
@@ -38,13 +37,13 @@ func (t Task) Format(p *Page) (string, []byte) {
 	if t.PostProcess != "" {
 		split := strings.Split(t.PostProcess, " ")
 		cmd := exec.Command(split[0], split[1:]...)
-		buf := new(bytes.Buffer)
 		cmd.Stdin = strings.NewReader(p.Content)
-		cmd.Stdout = buf
-		if err := cmd.Run(); err != nil {
+		cmd.Stderr = os.Stderr
+		output, err := cmd.Output()
+		if err != nil {
 			log.Fatal(err)
 		}
-		return path, buf.Bytes()
+		return path, output
 	}
 
 	return path, []byte(p.Content)