golang中命令行库cobra的使用方法示例

宇文娅绿

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。

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

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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

1. src> ..\bin\cobra.exe init demo
   
2. Your Cobra application is ready at
   
3. C:\Users\liubo5\Desktop\transcoding_tool\src\demo
   
4. Give it a try by going there and running `go run main.go`
   
5. Add commands to it by running `cobra add [cmdname]`

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在src目录下会生成一个demo的文件夹，如下：

1. ▾ demo
   
2.     ▾ cmd/
   
3.         root.go
   
4.     main.go

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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：

1. ▾ demo
   
2.     ▾ cmd/
   
3.         root.go
   
4.     ▾ imp/
   
5.         imp.go
   
6.         imp_test.go
   
7.     main.go

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imp.go文件的代码如下：

1. package imp
   
2. 
   
3. import(
   
4. "fmt"
   
5. )
   
6. 
   
7. func Show(name string, age int) {
   
8. fmt.Printf("My Name is %s, My age is %d\n", name, age)
   
9. }

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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：

1. // Copyright © 2016 NAME HERE <EMAIL ADDRESS>
   
2. //
   
3. // Licensed under the Apache License, Version 2.0 (the "License");
   
4. // you may not use this file except in compliance with the License.
   
5. // You may obtain a copy of the License at
   
6. //
   
7. //  http://www.apache.org/licenses/LICENSE-2.0
   
8. //
   
9. // Unless required by applicable law or agreed to in writing, software
   
10. // distributed under the License is distributed on an "AS IS" BASIS,
    
11. // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    
12. // See the License for the specific language governing permissions and
    
13. // limitations under the License.
    
14. 
    
15. package main
    
16. 
    
17. import "demo/cmd"
    
18. 
    
19. func main() {
    
20. cmd.Execute()
    
21. }

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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：

1. // Copyright © 2016 NAME HERE <EMAIL ADDRESS>
   
2. //
   
3. // Licensed under the Apache License, Version 2.0 (the "License");
   
4. // you may not use this file except in compliance with the License.
   
5. // You may obtain a copy of the License at
   
6. //
   
7. //  http://www.apache.org/licenses/LICENSE-2.0
   
8. //
   
9. // Unless required by applicable law or agreed to in writing, software
   
10. // distributed under the License is distributed on an "AS IS" BASIS,
    
11. // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    
12. // See the License for the specific language governing permissions and
    
13. // limitations under the License.
    
14. 
    
15. package cmd
    
16. 
    
17. import (
    
18. "fmt"
    
19. "os"
    
20. 
    
21. "github.com/spf13/cobra"
    
22. "github.com/spf13/viper"
    
23. )
    
24. 
    
25. var cfgFile string
    
26. 
    
27. // RootCmd represents the base command when called without any subcommands
    
28. var RootCmd = &cobra.Command{
    
29. Use: "demo",
    
30. Short: "A brief description of your application",
    
31. Long: `A longer description that spans multiple lines and likely contains
    
32. examples and usage of using your application. For example:
    
33. 
    
34. Cobra is a CLI library for Go that empowers applications.
    
35. This application is a tool to generate the needed files
    
36. to quickly create a Cobra application.`,
    
37. // Uncomment the following line if your bare application
    
38. // has an action associated with it:
    
39. // Run: func(cmd *cobra.Command, args []string) { },
    
40. }
    
41. 
    
42. // Execute adds all child commands to the root command sets flags appropriately.
    
43. // This is called by main.main(). It only needs to happen once to the rootCmd.
    
44. func Execute() {
    
45. if err := RootCmd.Execute(); err != nil {
    
46.   fmt.Println(err)
    
47.   os.Exit(-1)
    
48. }
    
49. }
    
50. 
    
51. func init() {
    
52. cobra.OnInitialize(initConfig)
    
53. 
    
54. // Here you will define your flags and configuration settings.
    
55. // Cobra supports Persistent Flags, which, if defined here,
    
56. // will be global for your application.
    
57. 
    
58. RootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file (default is $HOME/.demo.yaml)")
    
59. // Cobra also supports local flags, which will only run
    
60. // when this action is called directly.
    
61. RootCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
    
62. }
    
63. 
    
64. // initConfig reads in config file and ENV variables if set.
    
65. func initConfig() {
    
66. if cfgFile != "" { // enable ability to specify config file via flag
    
67.   viper.SetConfigFile(cfgFile)
    
68. }
    
69. 
    
70. viper.SetConfigName(".demo") // name of config file (without extension)
    
71. viper.AddConfigPath("$HOME") // adding home directory as first search path
    
72. viper.AutomaticEnv()   // read in environment variables that match
    
73. 
    
74. // If a config file is found, read it in.
    
75. if err := viper.ReadInConfig(); err == nil {
    
76.   fmt.Println("Using config file:", viper.ConfigFileUsed())
    
77. }
    
78. }

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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：

1. // Copyright © 2016 NAME HERE <EMAIL ADDRESS>
   
2. //
   
3. // Licensed under the Apache License, Version 2.0 (the "License");
   
4. // you may not use this file except in compliance with the License.
   
5. // You may obtain a copy of the License at
   
6. //
   
7. //  http://www.apache.org/licenses/LICENSE-2.0
   
8. //
   
9. // Unless required by applicable law or agreed to in writing, software
   
10. // distributed under the License is distributed on an "AS IS" BASIS,
    
11. // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    
12. // See the License for the specific language governing permissions and
    
13. // limitations under the License.
    
14. 
    
15. package cmd
    
16. 
    
17. import (
    
18. "fmt"
    
19. "os"
    
20. 
    
21. "github.com/spf13/cobra"
    
22. // "github.com/spf13/viper"
    
23. "demo/imp"
    
24. )
    
25. 
    
26. //var cfgFile string
    
27. var name string
    
28. var age int
    
29. 
    
30. // RootCmd represents the base command when called without any subcommands
    
31. var RootCmd = &cobra.Command{
    
32. Use: "demo",
    
33. Short: "A test demo",
    
34. Long: `Demo is a test appcation for print things`,
    
35. // Uncomment the following line if your bare application
    
36. // has an action associated with it:
    
37. Run: func(cmd *cobra.Command, args []string) {
    
38.   if len(name) == 0 {
    
39.    cmd.Help()
    
40.    return
    
41.   }
    
42.   imp.Show(name, age)
    
43. },
    
44. }
    
45. 
    
46. // Execute adds all child commands to the root command sets flags appropriately.
    
47. // This is called by main.main(). It only needs to happen once to the rootCmd.
    
48. func Execute() {
    
49. if err := RootCmd.Execute(); err != nil {
    
50.   fmt.Println(err)
    
51.   os.Exit(-1)
    
52. }
    
53. }
    
54. 
    
55. func init() {
    
56. // cobra.OnInitialize(initConfig)
    
57. 
    
58. // Here you will define your flags and configuration settings.
    
59. // Cobra supports Persistent Flags, which, if defined here,
    
60. // will be global for your application.
    
61. 
    
62. // RootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file (default is $HOME/.demo.yaml)")
    
63. // Cobra also supports local flags, which will only run
    
64. // when this action is called directly.
    
65. // RootCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
    
66. RootCmd.Flags().StringVarP(&name, "name", "n", "", "person's name")
    
67. RootCmd.Flags().IntVarP(&age, "age", "a", 0, "person's age")
    
68. }
    
69. 
    
70. // initConfig reads in config file and ENV variables if set.
    
71. //func initConfig() {
    
72. // if cfgFile != "" { // enable ability to specify config file via flag
    
73. //  viper.SetConfigFile(cfgFile)
    
74. // }
    
75. 
    
76. // viper.SetConfigName(".demo") // name of config file (without extension)
    
77. // viper.AddConfigPath("$HOME") // adding home directory as first search path
    
78. // viper.AutomaticEnv()   // read in environment variables that match
    
79. 
    
80. // // If a config file is found, read it in.
    
81. // if err := viper.ReadInConfig(); err == nil {
    
82. //  fmt.Println("Using config file:", viper.ConfigFileUsed())
    
83. // }
    
84. //}

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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：

1. >demo.exe
   
2. Demo is a test appcation for print things
   
3. Usage:
   
4.   demo [flags]
   
5. Flags:
   
6.   -a, --age int       person's age
   
7.   -h, --help          help for demo
   
8.   -n, --name string   person's name

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1. >demo -n borey --age 26
   
2. My Name is borey, My age is 26

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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：

1. src\demo>..\..\bin\cobra add test
   
2. test created at C:\Users\liubo5\Desktop\transcoding_tool\src\demo\cmd\test.go

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在src目录下demo的文件夹下生成了一个cmd\test.go文件，如下：

1. ▾ demo
   
2.     ▾ cmd/
   
3.         root.go
   
4.         test.go
   
5.     main.go

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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：

1. src\demo>demo
   
2. Demo is a test appcation for print things
   
3. 
   
4. Usage:
   
5. demo [flags]
   
6. demo [command]
   
7. 
   
8. Available Commands:
   
9. test  A brief description of your command
   
10. 
    
11. Flags:
    
12. -a, --age int  person's age
    
13. -h, --help   help for demo
    
14. -n, --name string person's name
    
15. 
    
16. Use "demo [command] --help" for more information about a command.

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可以看出demo既支持直接使用标记flag，又能使用子命令

1. src\demo>demo test -h
   
2. A longer description that spans multiple lines and likely contains examples
   
3. and usage of using your command. For example:
   
4. 
   
5. Cobra is a CLI library for Go that empowers applications.
   
6. This application is a tool to generate the needed files
   
7. to quickly create a Cobra application.
   
8. 
   
9. Usage:
   
10. demo test [flags]

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调用test命令输出信息，这里没有对默认信息进行修改。

1. src\demo>demo tst
   
2. Error: unknown command "tst" for "demo"
   
3. 
   
4. Did you mean this?
   
5.   test
   
6. 
   
7. Run 'demo --help' for usage.
   
8. unknown command "tst" for "demo"
   
9. 
   
10. Did you mean this?
    
11.   test

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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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感谢楼主，顶。