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：

▾ demo

▾ cmd/

root.go

main.go

如果你的demo程序没有subcommands，那么cobra生成应用程序的操作就结束了。

如何实现没有子命令的CLIs程序

接下来就是可以继续demo的功能设计了。例如我在demo下面新建一个包，名称为imp。如下：

▾ demo

▾ cmd/

root.go

▾ imp/

imp.go

imp_test.go

main.go

imp.go文件的代码如下：

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

//

// 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

//

// 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

//

// 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：

▾ demo

▾ cmd/

root.go

test.go

main.go

接下来的操作就和上面修改root.go文件一样去配置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?

test

Run 'demo --help' for usage.

unknown command "tst" for "demo"

Did you mean this?

test

这是错误命令提示功能

OVER

Cobra的使用就介绍到这里，更新细节可去github详细研究一下。这里只是一个简单的使用入门介绍，如果有错误之处，敬请指出，谢谢～

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