Read line of numbers in Go

I have the following input, where on the first line is N - count of numbers, and on the second line N numbers, separated by space:

5
2 1 0 3 4

In Python I can read numbers without specifying its count (N):

_ = input()
numbers = list(map(int, input().split()))

How can I do the same in Go? Or I have to know exactly how many numbers are?

You can iterate through a file line-by-line using bufio, and the strings module can split a string into a slice. So that gets us something like:

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	readFile, err := os.Open("data.txt")
	defer readFile.Close()

	if err != nil {
		fmt.Println(err)
	}
	fileScanner := bufio.NewScanner(readFile)

	fileScanner.Split(bufio.ScanLines)

	for fileScanner.Scan() {

		// get next line from the file
		line := fileScanner.Text()

		// split it into a list of space-delimited tokens
		chars := strings.Split(line, " ")

		// create an slice of ints the same length as
		// the chars slice
		ints := make([]int, len(chars))

		for i, s := range chars {
			// convert string to int
			val, err := strconv.Atoi(s)
			if err != nil {
				panic(err)
			}

			// update the corresponding position in the
			// ints slice
			ints[i] = val
		}

		fmt.Printf("%v\n", ints)
	}
}

Which given your sample data will output:

[5]
[2 1 0 3 4]

Since you know the delimiter and you only have 2 lines, this is also a more compact solution:

package main

import (
	"fmt"
	"os"
	"regexp"
	"strconv"
	"strings"
)

func main() {

	parts, err := readRaw("data.txt")
	if err != nil {
		panic(err)
	}

	n, nums, err := toNumbers(parts)
	if err != nil {
		panic(err)
	}

	fmt.Printf("%d: %v\n", n, nums)
}

// readRaw reads the file in input and returns the numbers inside as a slice of strings
func readRaw(fn string) ([]string, error) {
	b, err := os.ReadFile(fn)
	if err != nil {
		return nil, err
	}
	return regexp.MustCompile(`\s`).Split(strings.TrimSpace(string(b)), -1), nil
}

// toNumbers plays with the input string to return the data as a slice of int
func toNumbers(parts []string) (int, []int, error) {
	n, err := strconv.Atoi(parts[0])
	if err != nil {
		return 0, nil, err
	}
	nums := make([]int, 0)
	for _, p := range parts[1:] {
		num, err := strconv.Atoi(p)
		if err != nil {
			return n, nums, err
		}
		nums = append(nums, num)
	}

	return n, nums, nil
}

The output out be:

5: [2 1 0 3 4]