CLI input validation patterns¶
CLI input validation patterns encompass the logic used to ensure that command-line interfaces receive the expected data types, required arguments, and valid subcommands before execution.^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md]
Validation Logic¶
Input validation in a CLI typically serves two purposes: ensuring that required arguments are present and preventing the execution of invalid commands.^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md]
Required Field Checks¶
A common validation pattern involves checking if specific string pointers or flags are empty.^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md] If a required field is missing, the application should print usage instructions (often via PrintDefaults()) and exit with an error status^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md].
For example, when adding an item where all fields are mandatory, a validation function might check if any field is an empty string and trigger an error message if so^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md].
Mutually Exclusive or Conditional Logic¶
Validation logic often handles conditional requirements, such as ensuring that if a specific flag (like --all) is not set, an alternative identifier (like an --id) must be provided^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md]. This ensures the program has enough context to proceed.
Subcommand Validation¶
Before processing specific flags, a CLI application must validate the high-level command or action requested by the user (e.g., get vs. add)^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md].
A standard pattern for this involves checking the length of the arguments list (os.Args) to ensure at least a subcommand is present^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md]. If the argument count is insufficient (e.g., length < 2), the application typically prints an "expected subcommand" message and exits^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md].
Subsequently, a switch statement can be used to match the subcommand against known handlers (e.g., case "get") or default to an error state for unrecognized inputs^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md].