Golang命令行庫Cobra的使用

前言

Cobra既是用於創建強大的現代CLI應用程序的庫，也是用於生成應用程序和命令文件的程序。許多使用最廣泛的Go項目都是使用Cobra構建的，其中包括：
kubernetes
docker
openshift
...

一、安裝Cobra
在我們安裝Cobra之前，我們先解決大陸網絡無法訪問的問題（你懂得），否則是無法完成所有工具的安裝。這里我們使用Gopm來實現，gopm是Go Package Manager 的縮寫。是Golang上的包管理工具，十分好用。

1.1 gopm 安裝

go get -u github.com/gpmgo/gopm

這樣就將gopm完成了，在對應的$GOPATH/bin目錄下即可看到；

1.2 安裝Cobra

go get -g github.com/spf13/cobra/cobra
go build github.com/spf13/cobra/cobra

提示：在執行go install的時候，需要依賴golang.org/x/相關軟件包，請到該處下載即可。下載之后，將該包解壓到自己的$GOPATH/src目錄即可；

二、Cobra相關使用

2.1 使用Cobra生產應用程序

假設現在我們要開發一個基於CLI的命令程序，名字為demo。首先打開CMD，切換到GOPATH的bin目錄下，執行如下指令：

cobra init demo

在src目錄下會生成一個demo的文件夾，如下：

tree src/demo
src/demo
├── LICENSE
├── cmd
│   └── root.go
└── main.go

測試cobra效果：

demo go run main.go demo
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.

當初次創建完項目之后，即可使用項目(這里是"demo")來查看效果；

2.2 添加子命令（這里以51reboot培訓內容為例）

demo cobra add unbuf
unbuf created at /Users/yangsheng/go/src/demo/cmd/unbuf.go
demo tree
.
├── LICENSE
├── cmd
│   ├── root.go
│   └── unbuf.go
└── main.go

此時目錄結構變更為如上所示。現在我們來執行一下這個子命令：

go run main.go unbuf
unbuf called

2.3 完善子命令功能

創建unbuf代碼程序

mkdir unbuf

在該目錄下面新建文件unbuf.go文件，具體內容如下：

package unbuf

import (
    "fmt"
    "math/rand"
    "sync"
    "time"
)

func init() {
    rand.Seed(time.Now().UnixNano())
}

//Player xxx
type Player struct {
    User1 string
    User2 string
}

// NewPlayer  create a instance, Player is object
func NewPlayer(user1, user2 string) *Player {
    return &Player{
        User1: user1,
        User2: user2,
    }
}

func (p *Player) GoPlayer() {
    var wg sync.WaitGroup
    ch := make(chan int)
    wg.Add(2)
    go player(p.User1, ch, &wg)
    go player(p.User2, ch, &wg)
    ch <- 1
    wg.Wait()
}

//player  two players
func player(name string, ch chan int, wg *sync.WaitGroup) {
    defer wg.Done()
    for {
        ball, ok := <-ch
        if !ok {
            fmt.Printf("%s won!!!\n", name)
            break
        }
        n := rand.Intn(100)
        if n%15 == 0 {
            fmt.Printf("%s miss,the rand number is %d\n", name, n)
            close(ch)
            break
        }
        fmt.Printf("Player %s hit the ball %d,the rand number is %d\n", name, ball, n)
        ball++
        ch <- ball
    }
}

func Runner() {
    var wg sync.WaitGroup
    ch := make(chan int)
    wg.Add(1)
    go run(ch, &wg)
    ch <- 1
    wg.Wait()
}

func run(ch chan int, wg *sync.WaitGroup) {
    var newRunner int
    runner := <-ch
    fmt.Printf("runner %d running with Baton\n", runner)
    if runner != 4 {
        newRunner = runner + 1
        fmt.Printf("runner %d to the line\n", runner)
        go run(ch, wg)
    }
    // rand sleep time
    n := rand.Intn(100)
    time.Sleep(time.Duration(n) * time.Millisecond)
    if runner == 4 {
        fmt.Printf("runner %d finish,Race over\n", runner)
        wg.Done()
        return
    }
    fmt.Printf("runner %d exchange with runner %d\n", runner, newRunner)
    ch <- newRunner
}

對子命令進行完善，具體代碼如下：

// Copyright © 2018 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"

    "github.com/51reboot/golang-03-homework/lesson8/jkak/unbuf"
    "github.com/spf13/cobra"
)

// unbufCmd represents the unbuf command
var unbufCmd = &cobra.Command{
    Use:   "unbuf",
    Short: "A brief description of your command",
    Long: `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.`,
    Run: func(cmd *cobra.Command, args []string) {
        fmt.Println("unbuf called")
        // TODO: work your own magic here
        obj := unbuf.NewPlayer("chen", "song")
        obj.GoPlayer()

        fmt.Println("\n-- start running --\n")
        unbuf.Runner()
    },
}

func init() {
    rootCmd.AddCommand(unbufCmd)

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

    // Cobra supports Persistent Flags which will work for this command
    // and all subcommands, e.g.:
    // unbufCmd.PersistentFlags().String("foo", "", "A help for foo")

    // Cobra supports local flags which will only run when this command
    // is called directly, e.g.:
    // unbufCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
}

到此一個簡單demo功能就已經實現，我們運行一下看看實際效果：

go run main.go unbuf
unbuf called
Player song hit the ball 1,the rand number is 12
Player chen hit the ball 2,the rand number is 69
Player song hit the ball 3,the rand number is 58
Player chen hit the ball 4,the rand number is 77
Player song hit the ball 5,the rand number is 83
Player chen hit the ball 6,the rand number is 31
Player song hit the ball 7,the rand number is 16
Player chen hit the ball 8,the rand number is 67
Player song hit the ball 9,the rand number is 78
chen miss,the rand number is 15
song won!!!

-- start running --

runner 1 running with Baton
runner 1 to the line
runner 1 exchange with runner 2
runner 2 running with Baton
runner 2 to the line
runner 2 exchange with runner 3
runner 3 running with Baton
runner 3 to the line
runner 3 exchange with runner 4
runner 4 running with Baton
runner 4 finish,Race over

Cobra的使用就介紹到這里，更新細節可去github詳細研究一下。這里只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～

最后文中用到的代碼，如有侵權，請與我聯系；