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Command-line input validation

Command-line input validation is the process of verifying that arguments and flags provided to a command-line interface (CLI) application meet the expected criteria before the application executes its core logic^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md]. This ensures the application receives the necessary data to function correctly and provides helpful feedback to the user if the input is malformed^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md].

Validation typically occurs within handler functions dedicated to specific subcommands^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md].

Checking Required Fields

A common validation strategy is to ensure that mutually dependent arguments or required fields are present^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md]. For example, a command might require that if a "get all" flag is not set, a specific resource ID must be provided^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md].

if *all == false && *id == "" {
    fmt.Print("id is required or specify --all for all videos")
    getCmd.PrintDefaults()
    os.Exit(1)
}

^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md]

Multiple Field Validation

When a command accepts multiple inputs (such as adding a new record), validation often checks that none of the required fields are empty^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md]. This is frequently implemented by checking if a pointer to a flag value equals an empty string^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md].

if *id == "" || *title == "" || *url == "" || *imageUrl == "" || *description == "" {
    fmt.Print("all fields are required for adding a video")
    addCmd.PrintDefaults()
    os.Exit(1)
}

^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md]

User Feedback

When validation fails, the application should not proceed with execution^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md]. Instead, it should:

  1. Print an error message: Inform the user specifically what is wrong (e.g., "id is required")^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md].
  2. Display usage hints: Use functions like PrintDefaults() to show the user the available flags and their expected syntax^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md].
  3. Exit: Terminate the program with a non-zero status code (e.g., os.Exit(1)) to indicate an error state^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md].
  • [[Command-line parsing]]
  • [[Subcommands]]
  • [[Flag package]]

Sources

^[400-devops__09-Scripting-Language__golang__introduction__part-4.commandline__readme.md]