Random Doubt and Periodic Activities in Golang

Question

Is there any way I can get one executed fmt.Printf(choosenCity) every 6 hours and, at each run, he chooses a different element of the Array? I even managed to get him to perform periodically after a few gambiarras, but I read that it is not recommended to use time.sleep() and it always results in the same value, unless I close and run the script again.

arrCities := [6]string{
    "Teste1",
    "Teste2",
    "Teste3",
    "Teste4",
    "Teste5",
    "Teste6",
}
rand.Seed(time.Now().UnixNano())
choosenCity := arrCities[rand.Intn(len(arrCities))]

go func() {
        for true {
            fmt.Printf(choosenCity)
            time.Sleep(5 * time.Second)
        }
    }()
    // wait for 10 seconds before app finished
    time.Sleep(60 * time.Second)

}

//OBS a Função `go func()` está dentro da main()

I would like (without closing the script), every 6 hours, Pickar a random element of the Array, and then print.

Well, all the answers helped me in a way, I thought I could exemplify the problem with code syntax that I went through above. But in reality, what I desire is still a little different.

For more explanations:

Actually this "generator" of a random number, is to pull random data from an API. I thought with the example I gave in the post, I could do it, but I couldn’t. To explain better, here’s a snippet of code as I imagined it would work:

Choosen := fmt.Println(arrCities[r.Int64()]
URL := fmt.Sprintf("https://api.exemplo.io/data/?dado=%s", Choosen)
///... requisição e parsering da response
E então, aí, o "Ticker" que iria realizar tal atividade com a response da API.

///... requisição e parsering da response

//E AQUI VIRIA O TIMER 
fmt.Println(apiResults.Data1)
//

The question is that I need Random for the API and with the API answer, then yes, the Timer to perform

Answer 1

See if this example I made can help.

https://play.golang.org/p/pVlOFcmCnhO

I left a Sleep just so the program doesn’t run endlessly, but Voce can use something like the fmt.Scanln() to wait until some key is pressed or simply create some rule that leaves the systems running until something happens.

I hope I’ve helped.

Answer 2

When you use:

go func() {
        for true {
            fmt.Printf(choosenCity)
            time.Sleep(5 * time.Second)
        }
    }()
    // wait for 10 seconds before app finished
    time.Sleep(60 * time.Second)

}

You’re just printing the string choosenCity. I mean, it’s like doing: var choosenCity = "algum coisa" out of the loop. For this reason: "it always results in the same value".

---

You can just do:

go func() {
    for range time.Tick(1 * time.Second) {
            fmt.Println(arrCities[rand.Intn(len(cities))])
    }
}()

---

package main

import (
    "crypto/rand"
    "fmt"
    "math/big"
    "time"
)

var arrCities = []string{"Teste1", "Teste2", "Teste3", "Teste4", "Teste5", "Teste6"}

func main() {
    go func() {
        for range time.Tick(1 * time.Second) {
            l := big.NewInt(int64(len(arrCities)))
            if r, err := rand.Int(rand.Reader, l); err == nil {
                fmt.Println(arrCities[r.Int64()])
            }
        }
    }()

    select {} // Impede o fechamento.
}

https://play.golang.org/p/K2MV4HmQrHq