简介

Cobra既是一个用来创建强大的现代CLI命令行的golang库，也是一个生成程序应用和命令行文件的程序。下面是Cobra使用的一个演示：

Cobra提供的功能

• 简易的子命令行模式，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，串联flags
• 使用Cobra很容易的生成应用程序和命令，使用cobra create appname和cobra add cmdname
• 如果命令输入错误，将提供智能建议，如 app srver，将提示srver没有，是否是app server
• 自动生成commands和flags的帮助信息
• 自动生成详细的help信息，如app help
• 自动识别-h，--help帮助flag
• 自动生成应用程序在bash下命令自动完成功能
• 自动生成应用程序的man手册
• 命令行别名
• 自定义help和usage信息
• 可选的紧密集成的viper apps
  

如何使用

上面所有列出的功能我没有一一去使用，下面我来简单介绍一下如何使用Cobra，基本能够满足一般命令行程序的需求，如果需要更多功能，可以研究一下源码github。

安装cobra

Cobra是非常容易使用的，使用go get来安装最新版本的库。当然这个库还是相对比较大的，可能需要安装它可能需要相当长的时间，这取决于你的速网。安装完成后，打开GOPATH目录，bin目录下应该有已经编译好的cobra.exe程序，当然你也可以使用源代码自己生成一个最新的cobra程序。

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

使用cobra生成应用程序

假设现在我们要开发一个基于CLIs的命令程序，名字为demo。首先打开CMD，切换到GOPATH的src目录下[^1]，执行如下指令：
[^1]:cobra.exe只能在GOPATH目录下执行

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目录下会生成一个demo的文件夹，如下：

"htmlcode">

package imp

import(
 "fmt"
)

func Show(name string, age int) {
 fmt.Printf("My Name is %s, My age is %d\n", name, age)
}

demo程序成命令行接收两个参数name和age，然后打印出来。打开cobra自动生成的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函数执行cmd包，所以我们只需要在cmd包内调用imp包就能实现demo程序的需求。接着打开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())
 }
}

从源代码来看cmd包进行了一些初始化操作并提供了Execute接口。十分简单，其中viper是cobra集成的配置文件读取的库，这里不需要使用，我们可以注释掉（不注释可能生成的应用程序很大约10M，这里没哟用到最好是注释掉）。cobra的所有命令都是通过cobra.Command这个结构体实现的。为了实现demo功能，显然我们需要修改RootCmd。修改后的代码如下：

// 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的功能已经实现了，我们编译运行一下看看实际效果：

>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

如何实现带有子命令的CLIs程序

在执行cobra.exe init demo之后，继续使用cobra为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目录下demo的文件夹下生成了一个cmd\test.go文件，如下：

"htmlcode">

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既支持直接使用标记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]

调用test命令输出信息，这里没有对默认信息进行修改。

src\demo>demo tst
Error: unknown command "tst" for "demo"

Did you mean this"tst" for "demo"

Did you mean this"color: #ff0000">总结

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