簡介

Cobra既是一個用來建立強大的現代CLI指令行的golang庫，也是一個生成程式應用和指令行檔案的程式。下面是Cobra使用的一個示範：

Cobra提供的功能

簡易的子指令行模式，如 app server， app fetch等等
完全相容posix指令行模式
嵌套子指令subcommand
支援全局，局部，串聯flags
使用Cobra很容易的生成應用程式和指令，使用cobra create appname和cobra add cmdname
如果指令輸入錯誤，将提供智能建議，如 app srver，将提示srver沒有，是否是app server
自動生成commands和flags的幫助資訊
自動生成詳細的help資訊，如app help
自動識别-h，--help幫助flag
自動生成應用程式在bash下指令自動完成功能
自動生成應用程式的man手冊
指令行别名
自定義help和usage資訊
可選的緊密內建的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，基本能夠滿足一般指令行程式的需求，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。安裝完成後，打開GOPATH目錄，bin目錄下應該有已經編譯好的cobra.exe程式，當然你也可以使用源代碼自己生成一個最新的cobra程式。

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

使用cobra生成應用程式

假設現在我們要開發一個基于CLIs的指令程式，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：

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的檔案夾，如下：

▾ demo
    ▾ cmd/
        root.go
    main.go

如果你的demo程式沒有subcommands，那麼cobra生成應用程式的操作就結束了。

如何實作沒有子指令的CLIs程式

接下來就是可以繼續demo的功能設計了。例如我在demo下面建立一個包，名稱為imp。如下：

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

imp.go檔案的代碼如下：

package imp

import(
    "fmt"
)

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

demo程式成指令行接收兩個參數name和age，然後列印出來。打開cobra自動生成的main.go檔案檢視：

// 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，是以我們隻需要在cmd包内調用imp包就能實作demo程式的需求。接着打開root.go檔案檢視：

// 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內建的配置檔案讀取的庫，這裡不需要使用，我們可以注釋掉（不注釋可能生成的應用程式很大約10M，這裡沒喲用到最好是注釋掉）。cobra的所有指令都是通過cobra.Command這個結構體實作的。為了實作demo功能，顯然我們需要修改RootCmd。修改後的代碼如下：

// 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的功能已經實作了，我們編譯運作一下看看實際效果：

>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

如何實作帶有子指令的CLIs程式

在執行

cobra.exe init demo

之後，繼續使用cobra為demo添加子指令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的檔案夾下生成了一個cmd\test.go檔案，如下：

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

接下來的操作就和上面修改root.go檔案一樣去配置test子指令。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既支援直接使用标記flag，又能使用子指令

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指令輸出資訊，這裡沒有對預設資訊進行修改。

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

這是錯誤指令提示功能

OVER

Cobra的使用就介紹到這裡，更新細節可去github詳細研究一下。這裡隻是一個簡單的使用入門介紹，如果有錯誤之處，敬請指出，謝謝～

cobra.exe隻能在GOPATH目錄下執行 ↩︎

golang指令行庫cobra的使用

簡介

Cobra提供的功能

如何使用

安裝cobra

使用cobra生成應用程式

如何實作沒有子指令的CLIs程式

如何實作帶有子指令的CLIs程式

OVER

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