Version check program, from https://janithl.github.io/2019/12/a-simple-version-checker-in-go

versioncheck.go

package main

import (
	"encoding/json"
	"io/ioutil"
	"net/http"
	"os"
	"regexp"
	"time"
)

// Site type holds information about sites
type Site struct {
	Name, URL, Version, TimeTaken string
}

var sites = []Site{
	{"Site A", "https://a.web.site", "N/A", ""},
	{"Site B", "https://b.web.site", "N/A", ""},
	{"Site C", "https://c.web.site", "N/A", ""},
}

// Parser type holds information about the parsing
// A new instance of it is created on each scraping Goroutine
type Parser struct {
	url, body string
}

func (p *Parser) setURL(url string) {
	p.url = url
	p.body = ""
}

// getMatches tries to match the given regex and return the value
func (p *Parser) getMatches(regexString string, index int) string {
	regex, _ := regexp.Compile(regexString)

	matches := regex.FindStringSubmatch(p.body)
	if len(matches) == index+1 {
		return matches[index]
	}

	return "N/A"
}

// getVersion simply gets and reads the page body
func (p *Parser) getVersion() string {
	res, err := http.Get(p.url)
	if err != nil {
		return "Fetch Error"
	}

	body, err := ioutil.ReadAll(res.Body)
	res.Body.Close()
	if err != nil {
		return "Parse Error"
	}

	p.body = string(body)
	return p.getMatches("(<meta name=\"generator\" content=\")([^\"]+)", 2)
}

// getSiteVersion gets called in a loop, initialises a Parser, does the scrape,
// and does simple time keeping of how long a scrape takes
func getSiteVersion(key int, done chan<- bool) {
	start := time.Now() // to check the time taken

	site := Parser{}
	site.setURL(sites[key].URL)
	sites[key].Version = site.getVersion()
	sites[key].TimeTaken = time.Since(start).String()

	done <- true
}

func main() {
	// We're simply using a channel called done to make sure all
	// the Goroutines are done executing before we quit the application
	done := make(chan bool)
	for index := range sites {
		go getSiteVersion(index, done)
	}

	for i := 0; i < len(sites); i++ {
		<-done
	}

	// Finally, we output the sites slice as JSON
	enc := json.NewEncoder(os.Stdout)
	enc.Encode(sites)
}