Scanln in Golang doesn't accept whitespace

Question

How can I use Scanln that accepts whitespace as input?

Answer 1

You can't use the fmt package's Scanln() and similar functions for what you want to do, because quoting from fmt package doc:

Input processed by verbs is implicitly space-delimited: the implementation of every verb except %c starts by discarding leading spaces from the remaining input, and the %s verb (and %v reading into a string) stops consuming input at the first space or newline character.

The fmt package intentionally filters out whitespaces, this is how it is implemented.

Instead use bufio.Scanner to read lines that might contain white spaces which you don't want to filter out. To read / scan from the standard input, create a new bufio.Scanner using the bufio.NewScanner() function, passing os.Stdin.

Example:

scanner := bufio.NewScanner(os.Stdin)
if scanner.Scan() {
    line := scanner.Text()
    fmt.Printf("Input was: %q\n", line)
}

Now if you enter 3 spaces and press Enter, the output will be:

Input was: "   "

A more complete example that keeps reading lines until you terminate the app or enter "quit", and also checks if there was an error:

scanner := bufio.NewScanner(os.Stdin)
for scanner.Scan() {
    line := scanner.Text()
    fmt.Printf("Input was: %q\n", line)
    if line == "quit" {
        fmt.Println("Quitting...")
        break
    }
}
if err := scanner.Err(); err != nil {
    fmt.Println("Error encountered:", err)
}