goconcurrencystdinkeypressnonblocking

How to catch keypress without enter in Golang loop


I've got a loop in which some things happen according to the state it runs in (manual/automatic/learning). I now want to be able to let the program switch between these states by pressing the accompanying letters on the keyboard ("m" for manual, "a" for automatic and "l" for learning).

So to do this I need to be able to catch a keypress during the loop and change the variable status accordingly. I now have the following, which can catch a keypress followed by an enter:

ch := make(chan string)
go func(ch chan string) {
    reader := bufio.NewReader(os.Stdin)
    for {
        s, _ := reader.ReadString('\n')
        ch <- s
    }
}(ch)

for {
    select {
        case stdin, _ := <-ch:
            fmt.Println("Keys pressed:", stdin)
        default:
            fmt.Println("Working..")
    }
    time.Sleep(time.Second)
}

But the fact that I need to hit the enter button is not acceptable.

Does anybody know a non-blocking way to catch a keypress of a normal letter (not a SIGINT) without the need to hit enter afterwards?


Solution

  • After reading about os.Stdin.Read() and finding this answer I created the following code:

    package main
    
    import (
        "fmt"
        "os"
        "time"
        "os/exec"
    )
    
    func main() {
        ch := make(chan string)
        go func(ch chan string) {
            // disable input buffering
            exec.Command("stty", "-F", "/dev/tty", "cbreak", "min", "1").Run()
            // do not display entered characters on the screen
            exec.Command("stty", "-F", "/dev/tty", "-echo").Run()
            var b []byte = make([]byte, 1)
            for {
                os.Stdin.Read(b)
                ch <- string(b)
            }
        }(ch)
    
        for {
            select {
                case stdin, _ := <-ch:
                    fmt.Println("Keys pressed:", stdin)
                default:
                    fmt.Println("Working..")
            }
            time.Sleep(time.Millisecond * 100)
        }
    }
    

    This works like a charm.