Check the syntax of RMAN commands interactively without actually executing the commands
C:\Users\oracle>rman checksyntax
Recovery Manager: Release 18.0.0.0.0 - Production on Fri Apr 23 20:11:56 2021
Version 18.4.0.0.0
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
RMAN> backup database;
The command has no syntax errors