使用flag包做命令行参数解析 官方的example已经比较全面，可以满足一般的使用 根据官方example，使用方法可以总结为下面三步： 1. 定义全局变量来保存命令行参数值 2. 在init()函数中定义参数名与变量的关系 3. 在main()中执行flag.Parse() [Go 命令行解析 flag 包之通过子命令实现看 go 命令源码](https://zhuanlan.zhihu.com/p/94580903) [Go 命令行解析 flag 包之快速上手](https://mp.w

cmd_flag_ex1.go

// These examples demonstrate more intricate uses of the flag package.
package main

import (
	"errors"
	"flag"
	"fmt"
	"strings"
	"time"
)

// Example 1: A single string flag called "species" with default value "gopher".
var species = flag.String("species", "gopher", "the species we are studying")

// Example 2: Two flags sharing a variable, so we can have a shorthand.
// The order of initialization is undefined, so make sure both use the
// same default value. They must be set up with an init function.
var gopherType string

func init() {
	const (
		defaultGopher = "pocket"
		usage         = "the variety of gopher"
	)
	flag.StringVar(&gopherType, "gopher_type", defaultGopher, usage)
	flag.StringVar(&gopherType, "g", defaultGopher, usage+" (shorthand)")
}

// Example 3: A user-defined flag type, a slice of durations.
type interval []time.Duration

// String is the method to format the flag's value, part of the flag.Value interface.
// The String method's output will be used in diagnostics.
func (i *interval) String() string {
	return fmt.Sprint(*i)
}

// Set is the method to set the flag value, part of the flag.Value interface.
// Set's argument is a string to be parsed to set the flag.
// It's a comma-separated list, so we split it.
func (i *interval) Set(value string) error {
	// If we wanted to allow the flag to be set multiple times,
	// accumulating values, we would delete this if statement.
	// That would permit usages such as
	//	-deltaT 10s -deltaT 15s
	// and other combinations.
	if len(*i) > 0 {
		return errors.New("interval flag already set")
	}
	for _, dt := range strings.Split(value, ",") {
		duration, err := time.ParseDuration(dt)
		if err != nil {
			return err
		}
		*i = append(*i, duration)
	}
	return nil
}

// Define a flag to accumulate durations. Because it has a special type,
// we need to use the Var function and therefore create the flag during
// init.

var intervalFlag interval

func init() {
	// Tie the command-line flag to the intervalFlag variable and
	// set a usage message.
	flag.Var(&intervalFlag, "deltaT", "comma-separated list of intervals to use between events")
}

func main() {
	// All the interesting pieces are with the variables declared above, but
	// to enable the flag package to see the flags defined there, one must
	// execute, typically at the start of main (not init!):
	//	flag.Parse()
	// We don't run it here because this is not a main function and
	// the testing suite has already parsed the flags.
}

cmd_flag_ex2.go

// 显示usage
func main() {
    flag.Parse()
    if h {
        flag.Usage()
        return
    }

    cmdName := flag.Arg(0)
    switch cmdName {
    case "list":
        _ = list.Exec(cmdName, flag.Args()[1:])
    case "install":
        _ = install.Exec(cmdName, flag.Args()[1:])
    }
}

cmd_parse_flag.go

// 命令行使用方法:
// ./app --parm_name1 name1 --parm_name2

// step1: 定义命令行参数以及接收参数的变量
var (
	parm  = flag.String("parm_name1", "default_value", "description")
	parm2 = flag.Bool("parm_name2", false, "it's boolean value")
）

// step2: 
flag.Parse()

cmd_parse_flag_subcmd.go

package main

import (
    "flag"
    "fmt"
    "os"
)

func main() {

    fooCmd := flag.NewFlagSet("foo", flag.ExitOnError)
    fooEnable := fooCmd.Bool("enable", false, "enable")
    fooName := fooCmd.String("name", "", "name")

    barCmd := flag.NewFlagSet("bar", flag.ExitOnError)
    barLevel := barCmd.Int("level", 0, "level")

    if len(os.Args) < 2 {
        fmt.Println("expected 'foo' or 'bar' subcommands")
        os.Exit(1)
    }

    switch os.Args[1] {

    case "foo":
        fooCmd.Parse(os.Args[2:])
        fmt.Println("subcommand 'foo'")
        fmt.Println("  enable:", *fooEnable)
        fmt.Println("  name:", *fooName)
        fmt.Println("  tail:", fooCmd.Args())
    case "bar":
        barCmd.Parse(os.Args[2:])
        fmt.Println("subcommand 'bar'")
        fmt.Println("  level:", *barLevel)
        fmt.Println("  tail:", barCmd.Args())
    default:
        fmt.Println("expected 'foo' or 'bar' subcommands")
        os.Exit(1)
    }
}