k8s源码阅读基础 flag标准库(K8s source code reading basic Flag Standard Library)

参考文档:https://pkg.go.dev/flag@go1.18.2

应用:Package flag implements command-line flag parsing.

示例:util 包

package util

import (
	"fmt"
	"strings"
)

type StringList []string

func (sl *StringList) String() string {
	return fmt.Sprint(*sl)
}

func (sl *StringList) Set(value string) error {
	for _, s := range strings.Split(value, ",") {
		if len(s) == 0 {
			return fmt.Errorf("value should not be an empty string")
		}
		*sl = append(*sl, s)
	}
	return nil
}

main 包

package main

import (
	"TestGolang/util"
	"flag"
	"fmt"
)


//注意:port、address、apiPrefix均为指针类型
var (
	port                        = flag.Uint("port", 8080, "The port to listen on.  Default 8080.")
	address                     = flag.String("address", "127.0.0.1", "The address on the local server to listen to. Default 127.0.0.1")
	apiPrefix                   = flag.String("api_prefix", "/api/v1beta1", "The prefix for API requests on the server. Default '/api/v1beta1'")
	etcdServerList util.StringList
)

func init() {
	//Var方法使用指定的名字、使用信息注册一个flag。该flag的类型和值由第一个参数表示,该参数应实现了Value接口。
	flag.Var(&etcdServerList, "etcd_servers", "Value type is string; Servers for the etcd (http://ip:port), comma separated")
}

func main() {
	//从os.Args[1:]中解析注册的flag。 os.Args []string 保管了命令行参数,第一个是程序名。
	flag.Parse()

	fmt.Printf("port type is %T \n", port)

	fmt.Println("port:", *port)
	fmt.Println("address:", *address)
	fmt.Println("apiPrefix:", *apiPrefix)
	fmt.Println("etcdServerList:", etcdServerList)
}

help 效果:

D:\Projects\GolangProject\src\TestGolang>TestGolang.exe --help
Usage of TestGolang.exe:
  -address string
        The address on the local server to listen to. Default 127.0.0.1 (default "127.0.0.1")
  -api_prefix string
        The prefix for API requests on the server. Default '/api/v1beta1' (default "/api/v1beta1")
  -etcd_servers value
        Value type is string; Servers for the etcd (http://ip:port), comma separated
  -port uint
        The port to listen on.  Default 8080. (default 8080)

参数传递效果:

D:\Projects\GolangProject\src\TestGolang>TestGolang.exe -address "127.0.0.1" -api_prefix "/api/v1" -etcd_servers "http://192.168.1.2,http://192.168.1.3" -port 8090
port type is *uint
port: 8090
address: 127.0.0.1
apiPrefix: /api/v1
etcdServerList: [http://192.168.1.2 http://192.168.1.3]
————————

Reference documents: https://pkg.go.dev/flag @go1. eighteen point two

应用:Package flag implements command-line flag parsing.

Example: util package

package util

import (
	"fmt"
	"strings"
)

type StringList []string

func (sl *StringList) String() string {
	return fmt.Sprint(*sl)
}

func (sl *StringList) Set(value string) error {
	for _, s := range strings.Split(value, ",") {
		if len(s) == 0 {
			return fmt.Errorf("value should not be an empty string")
		}
		*sl = append(*sl, s)
	}
	return nil
}

main 包

package main

import (
	"TestGolang/util"
	"flag"
	"fmt"
)


//注意:port、address、apiPrefix均为指针类型
var (
	port                        = flag.Uint("port", 8080, "The port to listen on.  Default 8080.")
	address                     = flag.String("address", "127.0.0.1", "The address on the local server to listen to. Default 127.0.0.1")
	apiPrefix                   = flag.String("api_prefix", "/api/v1beta1", "The prefix for API requests on the server. Default '/api/v1beta1'")
	etcdServerList util.StringList
)

func init() {
	//Var方法使用指定的名字、使用信息注册一个flag。该flag的类型和值由第一个参数表示,该参数应实现了Value接口。
	flag.Var(&etcdServerList, "etcd_servers", "Value type is string; Servers for the etcd (http://ip:port), comma separated")
}

func main() {
	//从os.Args[1:]中解析注册的flag。 os.Args []string 保管了命令行参数,第一个是程序名。
	flag.Parse()

	fmt.Printf("port type is %T \n", port)

	fmt.Println("port:", *port)
	fmt.Println("address:", *address)
	fmt.Println("apiPrefix:", *apiPrefix)
	fmt.Println("etcdServerList:", etcdServerList)
}

Help effect:

D:\Projects\GolangProject\src\TestGolang>TestGolang.exe --help
Usage of TestGolang.exe:
  -address string
        The address on the local server to listen to. Default 127.0.0.1 (default "127.0.0.1")
  -api_prefix string
        The prefix for API requests on the server. Default '/api/v1beta1' (default "/api/v1beta1")
  -etcd_servers value
        Value type is string; Servers for the etcd (http://ip:port), comma separated
  -port uint
        The port to listen on.  Default 8080. (default 8080)

Parameter transfer effect:

D:\Projects\GolangProject\src\TestGolang>TestGolang.exe -address "127.0.0.1" -api_prefix "/api/v1" -etcd_servers "http://192.168.1.2,http://192.168.1.3" -port 8090
port type is *uint
port: 8090
address: 127.0.0.1
apiPrefix: /api/v1
etcdServerList: [http://192.168.1.2 http://192.168.1.3]