在 Golang 中使用 Cobra 创建 CLI 应用

$ APPNAME Command Args --Flags
# 或者
$ APPNAME Command --Flags Args

git clone URL -bare
go get -u URL
npm install package –save
kubectl get pods -n kube-system -l app=cobra

$ mkdir my-calc && cd my-calc
# 如果 go modules 默认没有开启，需要执行 export GO111MODULE=on 开启
$ go mod init my-calc
go: creating new go.mod: module my-calc

# 强烈推荐配置该环境变量
$ export GOPROXY=https://goproxy.cn
$ go get -u github.com/spf13/cobra/cobra

$ cobra init --pkg-name my-calc
Your Cobra applicaton is ready at
/Users/ych/devs/workspace/youdianzhishi/course/my-calc

$ tree .
.
├── LICENSE
├── cmd
│   └── root.go
├── go.mod
├── go.sum
└── main.go

1 directory, 5 files

// main.go
package main

import "my-calc/cmd"

func main() {
	cmd.Execute()
}

var rootCmd = &cobra.Command{
	Use:   "my-calc",
	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.
This application is a tool to generate the needed files
to quickly create a Cobra application.`,
	Run: func(cmd *cobra.Command, args []string) {
        fmt.Println("Hello Cobra CLI")
    },
}

$ go build -o my-calc

func initConfig() {
    fmt.Println("I'm inside initConfig function in cmd/root.go")
    ...
}

$ go build -o my-calc
$ ./my-calc
I'm inside initConfig function in cmd/root.go
Hello Cobra CLI

// cmd/root.go
func init() {
    fmt.Println("I'm inside init function in cmd/root.go")
    cobra.OnInitialize(initConfig)
    ...
}

func initConfig() {
    fmt.Println("I'm inside initConfig function in cmd/root.go")
    ...
}

// main.go
func main() {
     fmt.Println("I'm inside main function in main.go")
     cmd.Execute()
}

$ go build -o my-calc
$ ./my-calc
I'm inside init function in cmd/root.go
I'm inside main function in main.go
I'm inside initConfig function in cmd/root.go
Hello Cobra CLI

// cmd/root.go
// initConfig 读取配置文件和环境变量
func initConfig() {
	if cfgFile != "" {
        // 使用 flag 标志中传递的配置文件
		viper.SetConfigFile(cfgFile)
	} else {
		// 获取 Home 目录
		home, err := homedir.Dir()
		if err != nil {
			fmt.Println(err)
			os.Exit(1)
		}
		// 在 Home 目录下面查找名为 ".my-calc" 的配置文件
		viper.AddConfigPath(home)
		viper.SetConfigName(".my-calc")
	}
    // 读取匹配的环境变量
	viper.AutomaticEnv()
	// 如果有配置文件，则读取它
	if err := viper.ReadInConfig(); err == nil {
		fmt.Println("Using config file:", viper.ConfigFileUsed())
	}
}

$ cobra add add
add created at /Users/ych/devs/workspace/youdianzhishi/course/my-calc
$ tree .
.
├── LICENSE
├── cmd
│   ├── add.go
│   └── root.go
├── go.mod
├── go.sum
├── main.go
└── my-calc

1 directory, 7 files

$ go build -o my-calc
$ ./my-calc
Hello Cobra CLI
$ ./my-calc add
add called

// cmd/add.go
func intAdd(args []string) {
	var sum int
	// 循环 args 参数，循环的第一个值为 args 的索引，这里我们不需要，所以用 _ 忽略掉
	for _, ival := range args {
		// 将 string 转换成 int 类型
		temp, err := strconv.Atoi(ival)
		if err != nil {
			panic(err)
		}
		sum = sum + temp
	}
	fmt.Printf("Addition of numbers %s is %d\n", args, sum)
}

// addCmd
Run: func(cmd *cobra.Command, args []string) {
    intAdd(args)
},

$ go build -o my-calc
$ ./my-calc
Hello Cobra CLI
# 注意参数之间的空格
$ ./my-calc add 1 2 3
Addition of numbers [1 2 3] is 6

$ ./my-calc add 1 2 3.5
panic: strconv.Atoi: parsing "3.5": invalid syntax

goroutine 1 [running]:
my-calc/cmd.intAdd(0xc0000a5890, 0x3, 0x3)
......

// cmd/add.go
func init() {
	rootCmd.AddCommand(addCmd)
	addCmd.Flags().BoolP("float", "f", false, "Add Floating Numbers")
}

func floatAdd(args []string) {
	var sum float64
	for _, fval := range args {
		// 将字符串转换成 float64 类型
		temp, err := strconv.ParseFloat(fval, 64)
		if err != nil {
			panic(err)
		}
		sum = sum + temp
	}
	fmt.Printf("Sum of floating numbers %s is %f\n", args, sum)
}

// cmd/add.go
// addCmd
Run: func(cmd *cobra.Command, args []string) {
    // 获取 float 标识符的值，默认为 false
    fstatus, _ := cmd.Flags().GetBool("float")
    if fstatus { // 如果为 true，则调用 floatAdd 函数
        floatAdd(args)
    } else {
        intAdd(args)
    }
},

$ go build -o my-calc
$ ./my-calc add 1 2 3
Addition of numbers [1 2 3] is 6
$ ./my-calc add 1 2 3.5 -f
Sum of floating numbers [1 2 3.5] is 6.500000
$./my-calc add 1 2 3.5 --float
Sum of floating numbers [1 2 3.5] is 6.500000

$ cobra add even
even created at /Users/ych/devs/workspace/youdianzhishi/course/my-calc

// cmd/even.go
func init() {
	addCmd.AddCommand(evenCmd)
}

// cmd/even.go
Run: func(cmd *cobra.Command, args []string) {
    var evenSum int
    for _, ival := range args {
        temp, _ := strconv.Atoi(ival)
        if temp%2 == 0 {
            evenSum = evenSum + temp
        }
    }
    fmt.Printf("The even addition of %s is %d\n", args, evenSum)
},

$ go build -o my-calc
$ ./my-calc add even 1 2 3 4 5 6
The even addition of [1 2 3 4 5 6] is 12