使用gocmd构建Golang命令行应用程序

gocmd是一个轻量级的Golang库，用于快速构建命令行应用程序。它提供了参数解析、子命令、帮助文档生成等功能，非常适合开发CLI工具。下面我将详细介绍如何使用gocmd。

基本安装

首先安装gocmd库：

go get github.com/devfacet/gocmd

基本使用示例

package main

import (
	"fmt"
	"github.com/devfacet/gocmd"
)

func main() {
	// 定义命令选项
	options := []gocmd.Option{
		{
			Name:        "version",
			ShortName:   "v",
			Description: "Show version",
			Type:        gocmd.Bool,
		},
		{
			Name:        "config",
			ShortName:   "c",
			Description: "Config file path",
			Type:        gocmd.String,
		},
	}

	// 创建命令
	cmd := gocmd.NewCmd(gocmd.Options{
		Name:        "myapp",
		Version:     "1.0.0",
		Description: "A simple CLI application",
		Flags:       options,
		// 命令执行函数
		Func: func(cmd *gocmd.Cmd, args []string) error {
			if cmd.Flags.Bool["version"] {
				fmt.Println("Version:", cmd.Version)
				return nil
			}

			if path, ok := cmd.Flags.String["config"]; ok {
				fmt.Println("Using config file:", path)
			}

			fmt.Println("Hello from myapp!")
			return nil
		},
	})

	// 执行命令
	cmd.Run()
}

子命令支持

gocmd支持创建复杂的多级子命令结构：

package main

import (
	"fmt"
	"github.com/devfacet/gocmd"
)

func main() {
	cmd := gocmd.NewCmd(gocmd.Options{
		Name:        "myapp",
		Version:     "1.0.0",
		Description: "A CLI application with subcommands",
		Commands: []gocmd.Command{
			{
				Name:        "create",
				Description: "Create a resource",
				Flags: []gocmd.Option{
					{
						Name:        "name",
						Description: "Resource name",
						Type:        gocmd.String,
						Required:    true,
					},
				},
				Func: func(cmd *gocmd.Cmd, args []string) error {
					name := cmd.Flags.String["name"]
					fmt.Printf("Creating resource: %s\n", name)
					return nil
				},
			},
			{
				Name:        "delete",
				Description: "Delete a resource",
				Flags: []gocmd.Option{
					{
						Name:        "id",
						Description: "Resource ID",
						Type:        gocmd.Int,
						Required:    true,
					},
					{
						Name:        "force",
						Description: "Force deletion",
						Type:        gocmd.Bool,
					},
				},
				Func: func(cmd *gocmd.Cmd, args []string) error {
					id := cmd.Flags.Int["id"]
					force := cmd.Flags.Bool["force"]
					fmt.Printf("Deleting resource ID %d (force: %v)\n", id, force)
					return nil
				},
			},
		},
	})

	cmd.Run()
}

高级特性

1. 参数验证

Flags: []gocmd.Option{
	{
		Name:        "port",
		Description: "Server port",
		Type:        gocmd.Int,
		Validate: func(value interface{}) error {
			port := value.(int)
			if port < 1 || port > 65535 {
				return fmt.Errorf("port must be between 1 and 65535")
			}
			return nil
		},
	},
},

2. 自定义帮助信息

cmd := gocmd.NewCmd(gocmd.Options{
	Name:        "myapp",
	Description: "A custom CLI application",
	HelpStyle: gocmd.HelpStyle{
		Usage:       "Usage: myapp [global flags] <command> [command flags]",
		Description: "A longer description of what this application does",
		Examples: []string{
			"myapp create --name test",
			"myapp delete --id 123 --force",
		},
	},
	// ...其他配置
})

3. 环境变量支持

Flags: []gocmd.Option{
	{
		Name:        "api-key",
		Description: "API key for authentication",
		Type:        gocmd.String,
		EnvVar:      "MYAPP_API_KEY", // 从环境变量读取
	},
},

完整示例

下面是一个完整的CLI应用程序示例，包含多个子命令和复杂选项：

package main

import (
	"fmt"
	"os"

	"github.com/devfacet/gocmd"
)

func main() {
	// 主命令选项
	globalFlags := []gocmd.Option{
		{
			Name:        "verbose",
			ShortName:   "v",
			Description: "Enable verbose output",
			Type:        gocmd.Bool,
		},
		{
			Name:        "config",
			ShortName:   "c",
			Description: "Config file path",
			Type:        gocmd.String,
			Default:     "~/.myapp/config.yaml",
		},
	}

	cmd := gocmd.NewCmd(gocmd.Options{
		Name:        "myapp",
		Version:     "1.0.0",
		Description: "A complete CLI application example",
		Flags:       globalFlags,
		Commands: []gocmd.Command{
			{
				Name:        "user",
				Description: "User management",
				Commands: []gocmd.Command{
					{
						Name:        "create",
						Description: "Create a new user",
						Flags: []gocmd.Option{
							{
								Name:        "username",
								Description: "User login name",
								Type:        gocmd.String,
								Required:    true,
							},
							{
								Name:        "email",
								Description: "User email address",
								Type:        gocmd.String,
								Required:    true,
							},
							{
								Name:        "admin",
								Description: "Grant admin privileges",
								Type:        gocmd.Bool,
							},
						},
						Func: func(cmd *gocmd.Cmd, args []string) error {
							if cmd.Parent.Flags.Bool["verbose"] {
								fmt.Println("Verbose mode enabled")
							}
							fmt.Printf("Creating user %s (%s)", 
								cmd.Flags.String["username"],
								cmd.Flags.String["email"])
							if cmd.Flags.Bool["admin"] {
								fmt.Println(" with admin privileges")
							}
							return nil
						},
					},
					{
						Name:        "list",
						Description: "List all users",
						Func: func(cmd *gocmd.Cmd, args []string) error {
							fmt.Println("Listing all users...")
							// 实际应用中这里会查询并显示用户列表
							return nil
						},
					},
				},
			},
			{
				Name:        "server",
				Description: "Server operations",
				Flags: []gocmd.Option{
					{
						Name:        "port",
						Description: "Server port",
						Type:        gocmd.Int,
						Default:     8080,
					},
				},
				Func: func(cmd *gocmd.Cmd, args []string) error {
					fmt.Printf("Starting server on port %d\n", cmd.Flags.Int["port"])
					// 实际应用中这里会启动服务器
					return nil
				},
			},
		},
		Func: func(cmd *gocmd.Cmd, args []string) error {
			// 当没有子命令时显示帮助
			cmd.Help()
			return nil
		},
	})

	// 运行命令
	if err := cmd.Run(); err != nil {
		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
		os.Exit(1)
	}
}

总结

gocmd提供了以下主要功能：

1. 简单的命令行参数解析
2. 多级子命令支持
3. 自动生成帮助信息
4. 参数验证和默认值
5. 环境变量支持
6. 自定义帮助样式

相比标准库flag包，gocmd提供了更高级的功能和更友好的API，特别适合构建复杂的CLI应用程序。它比cobra更轻量，同时提供了足够的功能满足大多数CLI开发需求。

要了解更多高级用法，可以参考gocmd的官方文档和示例代码。