Golang 基於 flag 庫實現一個簡單命令行工具

import "flag"
var nFlag = flag.Int("n", 1234, "help message for flag n")

var flagvar int
func init() {
	flag.IntVar(&flagvar, "flagname", 1234, "help message for flagname")
}

fmt.Println("ip has value ", *ip)
fmt.Println("flagvar has value ", flagvar)

package main

import (
  "fmt"
  "flag"
)
var (
  intflag int
  boolflag bool
  stringflag string
)
func init() {
  flag.IntVar(&intflag, "intflag", 0, "int flag value")
  flag.BoolVar(&boolflag, "boolflag", false, "bool flag value")
  flag.StringVar(&stringflag, "stringflag", "default", "string flag value")
}
func main() {
  flag.Parse()

  fmt.Println("int flag:", intflag)
  fmt.Println("bool flag:", boolflag)
  fmt.Println("string flag:", stringflag)
}

$ ./main -intflag 12 -boolflag 1 -stringflag test

int flag: 12
bool flag: true
string flag: test

type FlagSet struct {
	// Usage is the function called when an error occurs while parsing flags.
	// The field is a function (not a method) that may be changed to point to
	// a custom error handler. What happens after Usage is called depends
	// on the ErrorHandling setting; for the command line, this defaults
	// to ExitOnError, which exits the program after calling Usage.
	Usage func()
	// contains filtered or unexported fields
}

// src/flag/flag.go
var CommandLine = NewFlagSet(os.Args[0], ExitOnError)

func Parse() {
  CommandLine.Parse(os.Args[1:])
}

func IntVar(p *int, name string, value int, usage string) {
  CommandLine.Var(newIntValue(value, p), name, usage)
}

func Int(name string, value int, usage string) *int {
  return CommandLine.Int(name, value, usage)
}

func NFlag() int { return len(CommandLine.actual) }

func Arg(i int) string {
  return CommandLine.Arg(i)
}

func NArg() int { return len(CommandLine.args) }

package main
import (
    "flag"
    "fmt"
    "os"
)
type arguments struct {
	weatherCity string
}
func (a *arguments) parseArgs(args []string) error {
	f := flag.NewFlagSet(os.Args[0], flag.ContinueOnError)

	f.StringVar(&a.weatherCity, "weather", "", "check weather")

	f.Usage = func() {
		fmt.Fprintf(os.Stderr, `flags: %s`, os.Args[0])
		f.PrintDefaults()
		os.Exit(1)
	}
	if err := f.Parse(args[1:]); err != nil {
		return err
	}

	return nil
}

func Execute() error {

	args := &arguments{}
	if err := args.parseArgs(os.Args); err != nil {
		fmt.Println(err)
		os.Exit(2)
	}

	// weather
	if args.weatherCity != "" {
                // TODO 實現根據 city 名稱拿天氣，並打印的效果
	}

	return nil
}

func GetWeather(city string) (string, error)

func getWeatherData(city string) string {
    url := "https://wttr.in/" + city
    response, err := http.Get(url)
    if err != nil {
            return "", err
    }
    all, err := ioutil.ReadAll(response.Body)
    if err != nil {
            return "", err
    }
    weather := string(all)
    return weather
}

package weather
import (
	"io/ioutil"
	"net/http"

	md "github.com/JohannesKaufmann/html-to-markdown"
	markdown "github.com/MichaelMure/go-term-markdown"
)
func GetWeather(city string) (string, error) {
	url := "https://wttr.in/" + city
	response, err := http.Get(url)
	if err != nil {
		return "", err
	}
	all, err := ioutil.ReadAll(response.Body)
	if err != nil {
		return "", err
	}
	weather := string(all)
	md := getMD(weather)
	result := markdown.Render(md, 280, 6)
	return string(result), nil
}

func getMD(html string) string {
	converter := md.NewConverter("", true, nil)
	markdown, err := converter.ConvertString(html)
	if err != nil {
		return ""
	}
	return markdown
}

$ opb -weather beijing