Add focused CLI argument helpers

internal/cli/root.go

@@ -82,3 +82,22 @@ func rejectExtraArgs(stderr io.Writer, command string, args []string) bool {
 	fmt.Fprintf(stderr, "%s: %s does not accept arguments: %s\n", app.Name, command, strings.Join(args, " "))
 	return true
 }
+
+func parseOptionalPathArg(stderr io.Writer, command string, args []string) (string, bool) {
+	if len(args) > 1 {
+		fmt.Fprintf(stderr, "%s: %s accepts at most one path\n", app.Name, command)
+		return "", false
+	}
+	if len(args) == 0 {
+		return "", true
+	}
+	return args[0], true
+}
+
+func rejectPositionalArgs(stderr io.Writer, command string, args []string) bool {
+	if len(args) == 0 {
+		return false
+	}
+	fmt.Fprintf(stderr, "%s: %s does not accept positional arguments: %v\n", app.Name, command, args)
+	return true
+}