feat: add optional out flag, simplify write step

README.md

@@ -32,6 +32,8 @@ Flags:
     	print generated contents, but do not write to file (optional)
   -force
     	force overwrite of existing contents (optional)
+  -out string
+        output file (optional, defaults to adding to source file)
 ```
 
 Examples:

cmd/mdtoc/main.go

@@ -11,6 +11,7 @@ import (
 
 var (
 	force, dryRun bool
+	out           string
 )
 
 func init() {
@@ -24,14 +25,15 @@ func init() {
 func main() {
 	flag.BoolVar(&force, "force", false, "force overwrite of existing contents (optional)")
 	flag.BoolVar(&dryRun, "dry-run", false, "print generated contents, but do not write to file (optional)")
+	flag.StringVar(&out, "out", "", "output file (optional, defaults to adding to source file)")
 	flag.Parse()
 
 	if flag.NArg() != 1 {
 		log.Fatal("unexpected number of args")
 	}
-	file := flag.Arg(0)
+	in := flag.Arg(0)
 
-	b, err := os.ReadFile(file)
+	b, err := os.ReadFile(in)
 	if err != nil {
 		log.Fatalf("reading file: %v", err)
 	}
@@ -54,26 +56,13 @@ func main() {
 		log.Fatalf("adding toc: %v", err)
 	}
 
-	err = overwrite(file, new)
-	if err != nil {
-		log.Fatalf("writing file: %v", err)
-	}
-}
-
-// overrwrite trucates an existing file and replaces with the content of b
-func overwrite(file string, b []byte) error {
-	f, err := os.OpenFile(file, os.O_WRONLY, 0664)
-	if err != nil {
-		log.Fatalf("opening file: %v", err)
+	target := in
+	if out != "" {
+		target = out
 	}
-	defer f.Close()
 
-	f.Truncate(0)
-	f.Seek(0, 0)
-	_, err = f.Write(b)
+	err = os.WriteFile(target, new, 0644)
 	if err != nil {
-		return err
+		log.Fatalf("writing file: %v", err)
 	}
-
-	return nil
 }