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簡介

Cobra既是一個用來創建強大的現代CLI命令行的golang庫，也是一個生成程序應用和命令行文件的程序。下面是Cobra使用的一個演示：

golang中命令行庫cobra的使用方法示例

Cobra提供的功能

簡易的子命令行模式，如 app server， app fetch等等
完全兼容posix命令行模式
嵌套子命令subcommand
支持全局，局部，串聯flags
使用Cobra很容易的生成應用程序和命令，使用cobra create appname和cobra add cmdname
如果命令輸入錯誤，將提供智能建議，如 app srver，將提示srver沒有，是否是app server
自動生成commands和flags的幫助信息
自動生成詳細的help信息，如app help
自動識別-h，--help幫助flag
自動生成應用程序在bash下命令自動完成功能
自動生成應用程序的man手冊
命令行別名
自定義help和usage信息
可選的緊密集成的viper apps

如何使用

上面所有列出的功能我沒有一一去使用，下面我來簡單介紹一下如何使用Cobra，基本能夠滿足一般命令行程序的需求，如果需要更多功能，可以研究一下源碼github。

安裝cobra

Cobra是非常容易使用的，使用go get來安裝最新版本的庫。當然這個庫還是相對比較大的，可能需要安裝它可能需要相當長的時間，這取決于你的速網。安裝完成后，打開GOPATH目錄，bin目錄下應該有已經編譯好的cobra.exe程序，當然你也可以使用源代碼自己生成一個最新的cobra程序。

				?

									> go get -v github.com/spf13/cobra/cobra

使用cobra生成應用程序

假設現在我們要開發一個基于CLIs的命令程序，名字為demo。首先打開CMD，切換到GOPATH的src目錄下[^1]，執行如下指令：
[^1]:cobra.exe只能在GOPATH目錄下執行

				?

									src> ..\bin\cobra.exe init demo 

									Your Cobra application is ready at

									C:\Users\liubo5\Desktop\transcoding_tool\src\demo

									Give it a try by going there and running `go run main.go`

									Add commands to it by running `cobra add [cmdname]`

在src目錄下會生成一個demo的文件夾，如下：

? demo
    ? cmd/
        root.go
    main.go

如果你的demo程序沒有subcommands，那么cobra生成應用程序的操作就結束了。

如何實現沒有子命令的CLIs程序

接下來就是可以繼續demo的功能設計了。例如我在demo下面新建一個包，名稱為imp。如下：

? demo
    ? cmd/
        root.go
    ? imp/
        imp.go
        imp_test.go
    main.go

imp.go文件的代碼如下：

				?

									package imp

									import(

									 "fmt"

									)

									func Show(name string, age int) {

									 fmt.Printf("My Name is %s, My age is %d\n", name, age)

									}

demo程序成命令行接收兩個參數name和age，然后打印出來。打開cobra自動生成的main.go文件查看：

				?

									// Copyright © 2016 NAME HERE <EMAIL ADDRESS>

									//

									// Licensed under the Apache License, Version 2.0 (the "License");

									// you may not use this file except in compliance with the License.

									// You may obtain a copy of the License at

									//

									//  http://www.apache.org/licenses/LICENSE-2.0

									//

									// Unless required by applicable law or agreed to in writing, software

									// distributed under the License is distributed on an "AS IS" BASIS,

									// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

									// See the License for the specific language governing permissions and

									// limitations under the License.

									package main

									import "demo/cmd"

									func main() {

									 cmd.Execute()

									}

可以看出main函數執行cmd包，所以我們只需要在cmd包內調用imp包就能實現demo程序的需求。接著打開root.go文件查看：

				?

									// Copyright © 2016 NAME HERE <EMAIL ADDRESS>

									//

									// Licensed under the Apache License, Version 2.0 (the "License");

									// you may not use this file except in compliance with the License.

									// You may obtain a copy of the License at

									//

									//  http://www.apache.org/licenses/LICENSE-2.0

									//

									// Unless required by applicable law or agreed to in writing, software

									// distributed under the License is distributed on an "AS IS" BASIS,

									// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

									// See the License for the specific language governing permissions and

									// limitations under the License.

									package cmd

									import (

									 "fmt"

									 "os"

									 "github.com/spf13/cobra"

									 "github.com/spf13/viper"

									)

									var cfgFile string

									// RootCmd represents the base command when called without any subcommands

									var RootCmd = &cobra.Command{

									 Use: "demo",

									 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.`,

									// Uncomment the following line if your bare application

									// has an action associated with it:

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

									}

									// Execute adds all child commands to the root command sets flags appropriately.

									// This is called by main.main(). It only needs to happen once to the rootCmd.

									func Execute() {

									 if err := RootCmd.Execute(); err != nil {

									  fmt.Println(err)

									  os.Exit(-1)

									 }

									}

									func init() {

									 cobra.OnInitialize(initConfig)

									 // Here you will define your flags and configuration settings.

									 // Cobra supports Persistent Flags, which, if defined here,

									 // will be global for your application.

									 RootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file (default is $HOME/.demo.yaml)")

									 // Cobra also supports local flags, which will only run

									 // when this action is called directly.

									 RootCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")

									}

									// initConfig reads in config file and ENV variables if set.

									func initConfig() {

									 if cfgFile != "" { // enable ability to specify config file via flag

									  viper.SetConfigFile(cfgFile)

									 }

									 viper.SetConfigName(".demo") // name of config file (without extension)

									 viper.AddConfigPath("$HOME") // adding home directory as first search path

									 viper.AutomaticEnv()   // read in environment variables that match

									 // If a config file is found, read it in.

									 if err := viper.ReadInConfig(); err == nil {

									  fmt.Println("Using config file:", viper.ConfigFileUsed())

									 }

									}

從源代碼來看cmd包進行了一些初始化操作并提供了Execute接口。十分簡單，其中viper是cobra集成的配置文件讀取的庫，這里不需要使用，我們可以注釋掉（不注釋可能生成的應用程序很大約10M，這里沒喲用到最好是注釋掉）。cobra的所有命令都是通過cobra.Command這個結構體實現的。為了實現demo功能，顯然我們需要修改RootCmd。修改后的代碼如下：

				?

									// Copyright © 2016 NAME HERE <EMAIL ADDRESS>

									//

									// Licensed under the Apache License, Version 2.0 (the "License");

									// you may not use this file except in compliance with the License.

									// You may obtain a copy of the License at

									//

									//  http://www.apache.org/licenses/LICENSE-2.0

									//

									// Unless required by applicable law or agreed to in writing, software

									// distributed under the License is distributed on an "AS IS" BASIS,

									// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

									// See the License for the specific language governing permissions and

									// limitations under the License.

									package cmd

									import (

									 "fmt"

									 "os"

									 "github.com/spf13/cobra"

									 // "github.com/spf13/viper"

									 "demo/imp"

									)

									//var cfgFile string

									var name string

									var age int

									// RootCmd represents the base command when called without any subcommands

									var RootCmd = &cobra.Command{

									 Use: "demo",

									 Short: "A test demo",

									 Long: `Demo is a test appcation for print things`,

									 // Uncomment the following line if your bare application

									 // has an action associated with it:

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

									  if len(name) == 0 {

									   cmd.Help()

									   return

									  }

									  imp.Show(name, age)

									 },

									}

									// Execute adds all child commands to the root command sets flags appropriately.

									// This is called by main.main(). It only needs to happen once to the rootCmd.

									func Execute() {

									 if err := RootCmd.Execute(); err != nil {

									  fmt.Println(err)

									  os.Exit(-1)

									 }

									}

									func init() {

									 // cobra.OnInitialize(initConfig)

									 // Here you will define your flags and configuration settings.

									 // Cobra supports Persistent Flags, which, if defined here,

									 // will be global for your application.

									 // RootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file (default is $HOME/.demo.yaml)")

									 // Cobra also supports local flags, which will only run

									 // when this action is called directly.

									 // RootCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")

									 RootCmd.Flags().StringVarP(&name, "name", "n", "", "person's name")

									 RootCmd.Flags().IntVarP(&age, "age", "a", 0, "person's age")

									}

									// initConfig reads in config file and ENV variables if set.

									//func initConfig() {

									// if cfgFile != "" { // enable ability to specify config file via flag

									//  viper.SetConfigFile(cfgFile)

									// }

									// viper.SetConfigName(".demo") // name of config file (without extension)

									// viper.AddConfigPath("$HOME") // adding home directory as first search path

									// viper.AutomaticEnv()   // read in environment variables that match

									// // If a config file is found, read it in.

									// if err := viper.ReadInConfig(); err == nil {

									//  fmt.Println("Using config file:", viper.ConfigFileUsed())

									// }

									//}

到此demo的功能已經實現了，我們編譯運行一下看看實際效果：

>demo.exe
Demo is a test appcation for print things

Usage:
demo [flags]

Flags:
-a, --age int       person's age
-h, --help          help for demo
-n, --name string   person's name

>demo -n borey --age 26
My Name is borey, My age is 26

如何實現帶有子命令的CLIs程序

在執行cobra.exe init demo之后，繼續使用cobra為demo添加子命令test：

				?

									src\demo>..\..\bin\cobra add test

									test created at C:\Users\liubo5\Desktop\transcoding_tool\src\demo\cmd\test.go

在src目錄下demo的文件夾下生成了一個cmd\test.go文件，如下：

? demo
    ? cmd/
        root.go
        test.go
    main.go

接下來的操作就和上面修改root.go文件一樣去配置test子命令。效果如下：

				?

									src\demo>demo

									Demo is a test appcation for print things

									Usage:

									 demo [flags]

									 demo [command]

									Available Commands:

									 test  A brief description of your command

									Flags:

									 -a, --age int  person's age

									 -h, --help   help for demo

									 -n, --name string person's name

									Use "demo [command] --help" for more information about a command.

可以看出demo既支持直接使用標記flag，又能使用子命令

				?

									src\demo>demo test -h

									A longer description that spans multiple lines and likely contains examples

									and usage of using your command. 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.

									Usage:

									 demo test [flags]

調用test命令輸出信息，這里沒有對默認信息進行修改。

				?

									src\demo>demo tst

									Error: unknown command "tst" for "demo"

									Did you mean this?

									  test

									Run 'demo --help' for usage.

									unknown command "tst" for "demo"

									Did you mean this?

									  test