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～
总结
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