Customizing Your CLI

In this tutorial, we’ll build upon the basic CLI from the previous tutorial and add customization features like flags, custom descriptions, and configuration options.

Prerequisites

Completed the My First CLI tutorial
Your my-cli project from the previous tutorial

Steps

Customize the Root Command Description

Let’s start by updating the main application description. Open the cmd/root.go file and see how we transform a basic command into a professional one:

Before

var rootCmd = &cobra.Command{
     Use:   "my-cli",
     Short: "A brief description of your application",
     Long: `A longer description that spans multiple lines and likely contains
   examples and usage of using your application. For example:

   Cobra is a CLI library for Go that empowers applications.`,
     // Uncomment the following line if your bare application
     // has an action associated with it:
     // Run: func(cmd *cobra.Command, args []string) { },
   }

After

var rootCmd = &cobra.Command{
     Use:   "my-cli",
     Short: "A powerful CLI tool built with Cobra",
     Long: `My CLI is a demonstration application built with Cobra.
   
   This application shows how to create professional command-line
   tools with proper flag handling, subcommands, and configuration.`,
     // Uncomment the following line if your bare application
     // has an action associated with it:
     // Run: func(cmd *cobra.Command, args []string) { },
   }

Add Global Flags

Let’s see how adding global flags transforms your CLI from basic to feature-rich. Here’s how the init() function evolves:

Before

func init() {
     rootCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
   }

After

var verbose bool
   
   func init() {
     rootCmd.PersistentFlags().BoolVarP(&verbose, "verbose", "v", false, "verbose output")
     rootCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
   }

Enhance the Serve Command

Watch how a simple serve command evolves into a fully-featured server command with flags and verbose output:

Before

var serveCmd = &cobra.Command{
     Use:   "serve",
     Short: "A brief description of your command",
     Long: `A longer description that spans multiple lines and likely contains
   examples and usage of using your command.`,
     Run: func(cmd *cobra.Command, args []string) {
       fmt.Println("serve called")
     },
   }
   
   func init() {
     rootCmd.AddCommand(serveCmd)
   }

After

var port int
   var host string
   
   var serveCmd = &cobra.Command{
     Use:   "serve",
     Short: "Start the application server",
     Long: `Start the application server on the specified host and port.
   
   The serve command will start a web server that can handle requests
   and provide API endpoints for your application.`,
     Run: func(cmd *cobra.Command, args []string) {
       if verbose {
         fmt.Printf("Starting server on %s:%d\n", host, port)
         fmt.Println("Verbose mode enabled")
       } else {
         fmt.Printf("Server starting on %s:%d\n", host, port)
       }
     },
   }
   
   func init() {
     rootCmd.AddCommand(serveCmd)
     serveCmd.Flags().IntVarP(&port, "port", "p", 8080, "Port to run the server on")
     serveCmd.Flags().StringVarP(&host, "host", "H", "localhost", "Host to bind the server to")
   }

Test Your Enhanced CLI

Build and test your updated CLI:

go build -o my-cli

./my-cli --help

A powerful CLI tool built with Cobra

My CLI is a demonstration application built with Cobra.

This application shows how to create professional command-line

tools with proper flag handling, subcommands, and configuration.

Usage:

my-cli [command]

Available Commands:

completion  Generate the autocompletion script for the specified shell

help        Help about any command

serve       Start the application server

Flags:

-h, --help      help for my-cli

-t, --toggle    Help message for toggle

-v, --verbose   verbose output

Test the Serve Command with Flags

Try out the serve command with different flag combinations:

./my-cli serve --help

Start the application server on the specified host and port.

The serve command will start a web server that can handle requests

and provide API endpoints for your application.

Usage:

my-cli serve [flags]

Flags:

-h, --help          help for serve

-H, --host string   Host to bind the server to (default "localhost")

-p, --port int      Port to run the server on (default 8080)

Global Flags:

-v, --verbose   verbose output

Test with custom port and verbose mode:

./my-cli serve --port 3000 --host 0.0.0.0 --verbose

Starting server on 0.0.0.0:3000

Verbose mode enabled

Add Input Validation

See how adding validation transforms your command from basic functionality to production-ready code:

Before

Run: func(cmd *cobra.Command, args []string) {
     if verbose {
       fmt.Printf("Starting server on %s:%d\n", host, port)
       fmt.Println("Verbose mode enabled")
     } else {
       fmt.Printf("Server starting on %s:%d\n", host, port)
     }
   },

After

Run: func(cmd *cobra.Command, args []string) {
     if port < 1 || port > 65535 {
       fmt.Fprintf(os.Stderr, "Error: port must be between 1 and 65535\n")
       os.Exit(1)
     }
     
     if verbose {
       fmt.Printf("Starting server on %s:%d\n", host, port)
       fmt.Println("Verbose mode enabled")
       fmt.Println("Configuration validated successfully")
     } else {
       fmt.Printf("Server starting on %s:%d\n", host, port)
     }
   },

Summary

In this tutorial, you’ve learned how to:

Customize command descriptions with the Short and Long fields
Add global flags that work across all commands using PersistentFlags()
Create command-specific flags with Flags()
Use different flag types (bool, int, string)
Implement flag shortcuts with single letters
Add basic input validation
Access global flags from subcommands

Your CLI now has proper help text, configurable options, and professional command-line behavior!

Next Steps

Try adding more commands with cobra-cli add [command-name]
Explore configuration files with Viper integration
Add persistent configuration and environment variable support