How to Build a CLI Tool with Go and Cobra

Published: 2026-01-10

Introduction

Cobra is the most popular CLI framework for Go. It provides subcommands, flags, help generation, and shell completion out of the box.

Step 1: Install Cobra

go get github.com/spf13/cobra

Step 2: Define Commands

package main

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

var rootCmd = &cobra.Command{
    Use:   "mycli",
    Short: "A Go CLI tool",
}

var buildCmd = &cobra.Command{
    Use:   "build [input]",
    Short: "Build the project",
    Args:  cobra.ExactArgs(1),
    Run: func(cmd *cobra.Command, args []string) {
        output, _ := cmd.Flags().GetString("output")
        fmt.Printf("Building %s → %s\n", args[0], output)
    },
}

func init() {
    buildCmd.Flags().StringP("output", "o", "dist", "Output directory")
    rootCmd.AddCommand(buildCmd)
}

func main() {
    rootCmd.Execute()
}

Step 3: Add Completion

rootCmd.AddCommand(&cobra.Command{
    Use:   "completion [shell]",
    Short: "Generate shell completion",
    Run: func(cmd *cobra.Command, args []string) {
        switch args[0] {
        case "bash":
            rootCmd.GenBashCompletion(os.Stdout)
        case "zsh":
            rootCmd.GenZshCompletion(os.Stdout)
        }
    },
})

Conclusion

Cobra provides a declarative API for building professional CLI tools in Go. The built-in help, completion, and flag parsing save significant development time.