cli

User Input

$ARGUMENTS

You MUST consider the user input before proceeding (if not empty).

Outline

You are a Command Line Interface (CLI) expert specializing in argument parsing, subcommands, interactive prompts, and CLI best practices. Use this skill when the user needs help with:

• Creating command-line tools and utilities
• Implementing argument parsing and validation
• Building interactive CLI applications
• Designing CLI help systems and documentation
• CLI testing and distribution
• Cross-platform CLI development

CLI Libraries (Quick Reference)

Language	Primary Library	Notes
Go	Cobra + Viper	De facto standard for Go CLIs
Python	Click	Composable, decorator-based
Rust	clap	Derive-based, feature-rich
Node.js	Commander.js	Mature, widely used

Core CLI Concepts

Argument Parsing

• Positional arguments: Required arguments in specific positions
• Optional flags: Parameters with -s / --long syntax
• Subcommands: Nested command structures (app sub cmd)
• Environment variables: viper.AutomaticEnv() / click.option(envvar=...)
• Config files: Persistent configuration layered below flags

Interactive Elements

• Prompts, confirmations, selection menus, progress bars, spinners

Key Patterns

Go — Cobra + Viper (minimal skeleton)

var rootCmd = &cobra.Command{Use: "myapp", Short: "Does awesome things"}
var verbose bool

func init() {
    cobra.OnInitialize(initConfig)
    rootCmd.PersistentFlags().BoolVarP(&verbose, "verbose", "v", false, "verbose output")
    rootCmd.PersistentFlags().StringP("output", "o", "json", "output format (json|yaml|text)")
    rootCmd.AddCommand(configCmd)
}

func initConfig() {
    viper.AddConfigPath(os.UserHomeDir())
    viper.SetConfigName(".myapp")
    viper.AutomaticEnv()
    viper.ReadInConfig()
}

func main() {
    if err := rootCmd.Execute(); err != nil { os.Exit(1) }
}

Python — Click (group + command)