golang常见库cobra

cobra 是 go 语言的一个库，能够用于编写命令行工具。一般咱们能够看到git pull 、docker container start 、apt install 等等这样命令，均可以很容易用corba来实现，另外，go 语言是很容易编译成一个二进制文件，本文将实现一个简单的命令行工具。

具体写一个例子, 设计一个命令叫blog， 有四个子命令

blog new [post-name] ：建立一篇新的blog
 blog list   ：列出当前有哪些文章
 blog delete [post-name]: 删除某一篇文章
 blog edit [post-name]：编辑某一篇文章

计划有如下几个步骤

• 建立模块
• 用cobra的命令行，建立命令行入口
• 用cobra的命令行，建立子命令
• 编写功能逻辑

建立模块

$ go mod init github.com/shalk/blog
go: creating new go.mod: module github.com/shalk/blog

建立命令行入口

说到命令行，可能会想到bash的getopt 或者 java 的jcommand，能够解析各类风格的命令行，可是一般这些命令行都有固定的写法，这个写法通常还记不住要找一个模板参考如下。cobra除了能够解析命令行以外，还提供了命令行，能够生成模板。先安装这个命令行, 而且把库的依赖加到go.mod里

$ go get -u github.com/spf13/cobra/cobra

cobra会安装到$GOPATH\bin 目录下，注意环境变量中把它加入PATH中

$ cobra init --pkg-name github.com/shalk/blog -a shalk -l mit
Your Cobra applicaton is ready at
D:\code\github.com\shalk\blog

目录结构以下:

./cmd
./cmd/root.go
./go.mod
./go.sum
./LICENSE
./main.go

编译一下

go build  -o blog .

执行一下

$blog -h
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.

命令行就建立好了，看上去一行代码也不用写，因为随着了解的深刻，后面须要调整生成的代码，仍是要了解一下cobra代码的套路。

cobra代码的套路

有三个概念，command、flag和args ，例如：

go get -u test.com/a/b

这里 get 就是commond（这里比较特殊）， -u 就是flag， test.com/a/b 就是args

那么命令行就是有三部分构成，因此须要定义好这个

• 命令自身的一些基本信息，用command表示，具体对象是 cobra.Command
• 命令的一些标致或者选项，用flag表示，具体对象是 flag.FlagSet
• 最后的参数，用args表示，一般是[]string

还有一个概念是子命令，好比get就是go的子命令，这是一个树状结构的关系。

我可使用go命令，也可使用 go get命令

例如: root.go，定义了root命令，另外在init里面 定义了flag，若是它自己有具体执行，就填充Run字段。

// rootCmd represents the base command when called without any subcommands
var rootCmd = &cobra.Command{
    Use:   "blog",
    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 and 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/.blog.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")

}

若是须要子命令，就须要在init 里，给 rootCmd.AddCommand() 其余的command，其余的子命令一般也会单独用一个文件编写，而且有一个全局变量，让rootCmd能够add它

建立子命令

D:\code\github.com\shalk\blog>cobra add  new
new created at D:\code\github.com\shalk\blog

D:\code\github.com\shalk\blog>cobra add  delete
delete created at D:\code\github.com\shalk\blog

D:\code\github.com\shalk\blog>cobra add  list
list created at D:\code\github.com\shalk\blog

D:\code\github.com\shalk\blog>cobra add  edit
edit created at D:\code\github.com\shalk\blog

cmd 目录下增长了 new.go, delete.go,list.go,edit.go

增长功能代码

new.go

var newCmd = &cobra.Command{
    Use:   "new",
    Short: "create new post",
    Long:  `create new post `,
    Args: func(cmd *cobra.Command, args []string) error {
        if len(args) != 1 {
            return errors.New("requires a color argument")
        }
        return nil
    },
    Run: func(cmd *cobra.Command, args []string) {
        fileName := "posts/" + args[0]
        err := os.Mkdir("posts", 644)
        if err != nil {
            log.Fatal(err)
        }
        _, err = os.Stat( fileName)
        if os.IsNotExist(err) {
            file, err := os.Create(fileName)
            if err != nil {
                log.Fatal(err)
            }
            log.Printf("create file %s", fileName)
            defer file.Close()
        } else {
        }
    },
}

list.go

var listCmd = &cobra.Command{
    Use:   "list",
    Short: "list all blog in posts",
    Long: `list all blog in posts `,
    Run: func(cmd *cobra.Command, args []string) {
        _, err := os.Stat("posts")
        if os.IsNotExist(err) {
            log.Fatal("posts dir is not exits")
        }
        dirs, err := ioutil.ReadDir("posts")
        if err != nil {
            log.Fatal("read posts dir fail")
        }
        fmt.Println("------------------")
        for _, dir := range dirs {
            fmt.Printf(" %s\n", dir.Name() )
        }
        fmt.Println("------------------")
        fmt.Printf("total: %d blog\n", len(dirs))

    },
}

delete.go

var deleteCmd = &cobra.Command{
    Use:   "delete",
    Short: "delete a post",
    Long: `delete a post`,
    Args: func(cmd *cobra.Command, args []string) error {
        if len(args) != 1 {
            return errors.New("requires a color argument")
        }
        if strings.Contains(args[0],"/") || strings.Contains(args[0],"..") {
            return errors.New("posts name should not contain / or .. ")
        }
        return nil
    },
    Run: func(cmd *cobra.Command, args []string) {
        fileName := "./posts/" +  args[0]
        stat, err := os.Stat(fileName)
        if os.IsNotExist(err) {
            log.Fatalf("post %s is not exist", fileName)
        }
        if stat.IsDir() {
            log.Fatalf("%s is dir ,can not be deleted", fileName)
        }
        err = os.Remove(fileName)
        if err != nil {
            log.Fatalf("delete %s fail, err %v", fileName, err)
        } else {
            log.Printf("delete post %s success", fileName)
        }
    },
}

edit.go 这个有一点麻烦，由于若是调用一个程序好比vim 打开文件，而且golang程序自己要退出，须要detach。暂时放一下（TODO）

编译测试

我是window测试，linux 更简单一点

PS D:\code\github.com\shalk\blog> go build -o blog.exe .
PS D:\code\github.com\shalk\blog> .\blog.exe list
------------------
------------------
total: 0 blog
PS D:\code\github.com\shalk\blog> .\blog.exe new blog1.md
2020/07/26 22:37:15 create file posts/blog1.md
PS D:\code\github.com\shalk\blog> .\blog.exe new blog2.md
2020/07/26 22:37:18 create file posts/blog2.md
PS D:\code\github.com\shalk\blog> .\blog.exe new blog3.md
2020/07/26 22:37:20 create file posts/blog3.md
PS D:\code\github.com\shalk\blog> .\blog list
------------------
 blog1.md
 blog2.md
 blog3.md
------------------
total: 3 blog
PS D:\code\github.com\shalk\blog> .\blog delete blog1.md
2020/07/26 22:37:37 delete post ./posts/blog1.md success
PS D:\code\github.com\shalk\blog> .\blog list
------------------
 blog2.md
 blog3.md
------------------
total: 2 blog
PS D:\code\github.com\shalk\blog> ls .\posts\


    目录: D:\code\github.com\shalk\blog\posts


Mode                LastWriteTime         Length Name
----                -------------         ------ ----
-a----        2020/7/26     22:37              0 blog2.md
-a----        2020/7/26     22:37              0 blog3.md


PS D:\code\github.com\shalk\blog>

小结

cobra 是一个高效的命令行解析库，利用cobra的脚手架，能够快速的实现一个命令行工具。若是须要更细致的控制，能够参考cobra的官方文档。