第一个库 Cobra

1. Cobra库介绍

1. 学习资料：https://juejin.cn/post/6983299467537547294
2. github：https://github.com/spf13/cobra

2. 库学习

2.1 源码库例子解析

package main

import (
 "fmt"
 "strings"
 "github.com/spf13/cobra"
)

func main() {
 var echoTimes int

 var cmdPrint = &cobra.Command{
   Use:   "print [string to print]",
   Short: "Print anything to the screen",
   Long: `print is for printing anything back to the screen.
For many years people have printed back to the screen.`,
   Args: cobra.MinimumNArgs(1),
   Run: func(cmd *cobra.Command, args []string) {
     fmt.Println("Print: " + strings.Join(args, " "))
   },
 }

 var cmdEcho = &cobra.Command{
   Use:   "echo [string to echo]",
   Short: "Echo anything to the screen",
   Long: `echo is for echoing anything back.
Echo works a lot like print, except it has a child command.`,
   Args: cobra.MinimumNArgs(1),
   Run: func(cmd *cobra.Command, args []string) {
     fmt.Println("Echo: " + strings.Join(args, " "))
   },
 }

 var cmdTimes = &cobra.Command{
   Use:   "times [string to echo]",
   Short: "Echo anything to the screen more times",
   Long: `echo things multiple times back to the user by providing
a count and a string.`,
   Args: cobra.MinimumNArgs(1),
   Run: func(cmd *cobra.Command, args []string) {
     for i := 0; i < echoTimes; i++ {
       fmt.Println("Echo: " + strings.Join(args, " "))
     }
   },
 }

 cmdTimes.Flags().IntVarP(&echoTimes, "times", "t", 1, "times to echo the input")

 var rootCmd = &cobra.Command{Use: "app"}
 rootCmd.AddCommand(cmdPrint, cmdEcho)
 cmdEcho.AddCommand(cmdTimes)
 rootCmd.Execute()
} 

1. Args：可以对于参数进行相关的校验，提供的校验方式有

NoArgs - the command will report an error if there are any positional args.
ArbitraryArgs - the command will accept any args.
OnlyValidArgs - the command will report an error if there are any positional args that are not in the ValidArgs field of Command.
MinimumNArgs(int) - the command will report an error if there are not at least N positional args.
MaximumNArgs(int) - the command will report an error if there are more than N positional args.
ExactArgs(int) - the command will report an error if there are not exactly N positional args.
ExactValidArgs(int) - the command will report an error if there are not exactly N positional args OR if there are any positional args that are not in the ValidArgs field of Command
RangeArgs(min, max) - the command will report an error if the number of args is not between the minimum and maximum number of expected args.

2. 一个层级可以加多个方法，一个方法上可以在追加嵌套一个方法

1. rootCmd.AddCommand(func1,func2...)： 一个层级追加多个方法
2. func1.AddCommand(subFunc1, subFunc2...):在追加嵌套一个方法

3. 参数解析方式

• cmdTimes.Flags().类型：只有当前的命令可以使用该参数
• cmdTimes. PersistentFlags().类型：当前命令以及该命令的子命令都需要支持；
• rootCmd.MarkFlagRequired("region")：对于如果没有设置region参数的命令就会有问题

4. 添加Hook

• PreRun：真正的Run开始执行前先操作的步骤
• PostRun：真正的Run执行后的操作