feat(cli): skip export dir-empty check (#314)

* feat(cli): skip export dir-empty check

Adds a `--force` flag to `tk export` to skip the check that makes sure
the output dir is empty.

This can be used to merge resources of multiple environments into a
single tree

* feat: check for file existence

Author: sh0rez

cmd/tk/export.go

@@ -36,6 +36,7 @@ func exportCmd() *cli.Command {
 	getExtCode := extCodeParser(cmd.Flags())
 	format := cmd.Flags().String("format", "{{.apiVersion}}.{{.kind}}-{{.metadata.name}}", "https://tanka.dev/exporting#filenames")
 	extension := cmd.Flags().String("extension", "yaml", "File extension")
+	merge := cmd.Flags().Bool("merge", false, "Allow merging with existing directory")
 
 	templateFuncMap := template.FuncMap{
 		"lower": func(s string) string {
@@ -50,8 +51,8 @@ func exportCmd() *cli.Command {
 		if err != nil {
 			return fmt.Errorf("Checking target dir: %s", err)
 		}
-		if !empty {
-			return fmt.Errorf("Target dir `%s` not empty. Aborting.", to)
+		if !empty && !*merge {
+			return fmt.Errorf("Output dir `%s` not empty. Pass --merge to ignore this", to)
 		}
 
 		// exit early if the template is bad
@@ -87,10 +88,18 @@ func exportCmd() *cli.Command {
 
 			// Create all subfolders in path
 			path := filepath.Join(to, name+"."+*extension)
+
+			// Abort if already exists
+			if ok, err := fileExists(path); err != nil {
+				return err
+			} else if !ok {
+				return fmt.Errorf("File '%s' already exists. Aborting", path)
+			}
+
+			// Write file
 			if err := os.MkdirAll(filepath.Dir(path), 0700); err != nil {
 				return fmt.Errorf("creating filepath '%s': %s", filepath.Dir(path), err)
 			}
-
 			data := m.String()
 			if err := ioutil.WriteFile(path, []byte(data), 0644); err != nil {
 				return fmt.Errorf("writing manifest: %s", err)
@@ -102,6 +111,14 @@ func exportCmd() *cli.Command {
 	return cmd
 }
 
+func fileExists(name string) (bool, error) {
+	_, err := os.Stat(name)
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+	return err != nil, err
+}
+
 func dirEmpty(dir string) (bool, error) {
 	f, err := os.Open(dir)
 	if os.IsNotExist(err) {