Go CLI Development

Go CLI Development with Cobra

This skill guides the development of CLI commands for tfskel using cobra and viper.

Command Structure

Each command should be in its own file under cmd/:

package cmd

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

var initCmd = &cobra.Command{
    Use:   "init [flags]",
    Short: "Initialize a new Terraform project structure",
    Long: `Initialize a new Terraform project with best-practice directory structure.

Creates environment directories (dev, stg, prd) with regional subdirectories,
and sets up linting configuration files.`,
    Example: `  # Initialize with default settings
  tfskel init

  # Initialize with custom environments and regions
  tfskel init --envs dev,stg,prd --regions eu-central-1,us-east-1`,
    RunE: runInit,
}

func init() {
    rootCmd.AddCommand(initCmd)

    initCmd.Flags().StringP("project-name", "p", "", "Project name")
    initCmd.Flags().StringSliceP("envs", "e", []string{"dev", "stg", "prd"}, "Environments to create")
    initCmd.Flags().StringSliceP("regions", "r", []string{"eu-central-1"}, "AWS regions")
}

func runInit(cmd *cobra.Command, args []string) error {
    // Implementation
    return nil
}

Flag Handling

• Use viper for configuration hierarchy (flags > env vars > config file > defaults)
• Always provide sensible defaults
• Validate flags early in RunE function

func runInit(cmd *cobra.Command, args []string) error {
    // Bind flags to viper
    viper.BindPFlag("project-name", cmd.Flags().Lookup("project-name"))

    // Get values with fallback
    projectName := viper.GetString("project-name")
    if projectName == "" {
        projectName = filepath.Base(getCurrentDir())
    }

    // Validate
    if err := validateProjectName(projectName); err != nil {
        return fmt.Errorf("invalid project name: %w", err)
    }

    // Execute logic
    return createProjectStructure(projectName, ...)
}

Error Handling

1. Return errors from RunE, don't call os.Exit()
2. Provide actionable error messages
3. Use error wrapping for context

if err := os.MkdirAll(path, 0755); err != nil {
    return fmt.Errorf("failed to create directory %s: %w", path, err)
}

Output Formatting

• Use consistent output formatting:

import "github.com/fatih/color"

var (
    successMsg = color.New(color.FgGreen).SprintFunc()
    errorMsg   = color.New(color.FgRed).SprintFunc()
    infoMsg    = color.New(color.FgCyan).SprintFunc()
)

fmt.Printf("%s Project initialized successfully\n", successMsg("✓"))
fmt.Printf("%s Created directory: %s\n", infoMsg("→"), path)

Testing Commands

• Test commands using buffer capture:

func TestInitCommand(t *testing.T) {
    cmd := &cobra.Command{}
    buf := new(bytes.Buffer)
    cmd.SetOut(buf)

    err := runInit(cmd, []string{})
    assert.NoError(t, err)
    assert.Contains(t, buf.String(), "initialized successfully")
}

Converted and distributed by TomeVault — claim your Tome and manage your conversions.