golang-cobra-development

name	golang-cobra-development
description	Use when building CLI commands, adding flags, creating subcommands, or integrating Viper configuration in this Go project

Go Cobra CLI Development

Overview

Patterns for building CLI applications with Cobra and Viper in huly-cli.

Project Structure

src/huly/
├── main.go              # Entry point
├── cmd/
│   ├── root.go          # Root command, global flags
│   └── version.go       # Version subcommand
├── internal/            # Private packages
└── version/
    └── version.go       # Build-time version variables

Adding a New Command

Create cmd/<command>.go:

package cmd

import (
    "fmt"
    "github.com/spf13/cobra"
)

var exampleCmd = &cobra.Command{
    Use:   "example",
    Short: "Short description",
    Long:  `Longer description.`,
    RunE: func(cmd *cobra.Command, args []string) error {
        name, _ := cmd.Flags().GetString("name")
        fmt.Printf("Hello, %s!\n", name)
        return nil
    },
}

func init() {
    rootCmd.AddCommand(exampleCmd)
    exampleCmd.Flags().StringP("name", "n", "world", "Name to greet")
}

Subcommands

var parentCmd = &cobra.Command{Use: "parent", Short: "Parent command"}
var childCmd = &cobra.Command{
    Use:   "child",
    Short: "Child command",
    RunE: func(cmd *cobra.Command, args []string) error {
        return nil
    },
}

func init() {
    rootCmd.AddCommand(parentCmd)
    parentCmd.AddCommand(childCmd)
}

Flags

Type	Method	Example
Persistent	PersistentFlags()	Available to command + subcommands
Local	Flags()	Only this command
Required	MarkFlagRequired()	Must be provided

// Persistent (inherited by subcommands)
rootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file")

// Local (only this command)
exampleCmd.Flags().BoolP("verbose", "v", false, "verbose output")

// Required
exampleCmd.MarkFlagRequired("name")

Viper Integration

func init() {
    exampleCmd.Flags().String("server", "localhost", "server address")
    viper.BindPFlag("server", exampleCmd.Flags().Lookup("server"))
}

func run(cmd *cobra.Command, args []string) error {
    // Checks: flag → env → config file → default
    server := viper.GetString("server")
    return nil
}

Error Handling

Always use RunE for proper error handling:

RunE: func(cmd *cobra.Command, args []string) error {
    if err := doThing(); err != nil {
        return fmt.Errorf("failed: %w", err)
    }
    return nil
}

Version Injection

Build with ldflags:

just build  # Injects version.Version, version.Commit, version.BuildDate

Quick Reference

Task	Code
Add command	rootCmd.AddCommand(cmd)
String flag	cmd.Flags().StringP("name", "n", "default", "help")
Bool flag	cmd.Flags().BoolP("verbose", "v", false, "help")
Get flag	cmd.Flags().GetString("name")
Viper get	viper.GetString("key")
Required	cmd.MarkFlagRequired("name")

References

• Cobra Documentation
• Cobra User Guide
• Viper Documentation