golang erase symbols from console

Question

I want to create animation in console, when program waits. There are a lot of simple ways to do this, usually, we just draw symbols in iterations of some cycle. Let our code be:

func Spinner(delay time.Duration) {
    for !StopSpinner{
        for _, r := range `-\|/` {
            fmt.Printf("\r%c", r)
            time.Sleep(delay)
        }
    }
}

The problem is - how to remove animation, when there is no need in it from the console screen. I tried escape sequences like fmt.Print("\b") or fmt.Printf("\r%s", "") but no result. I can not remove last symbol from screen and it concatenates with next text. How do you erase characters already printed to the console?

How to do this depends on which OS you're using. If you're on a Unix-like OS, something like [goncurses](https://github.com/rthornton128/goncurses) may be what you need. — Jonathan Hall, Jan 10 '18 at 14:56
Hello! My app is crossplatform, so I need to work with *nix and Windows too. — Олег Сидоров, Jan 10 '18 at 15:25

score 9 · Answer 1 · edited Nov 26 '18 at 12:12

9

All you need to do is print a space (0x20) when you are done and that will overwrite the spinner.

ie: fmt.Fprint(os.Stdout, "\r \r") to put the cursor back to beginning of line after the space.

edited Nov 26 '18 at 12:12

Hasibul Hasn

318
5
16

answered Jan 10 '18 at 16:03

David Budworth

11,248
1
36
45

score 4 · Answer 2 · answered Jan 16 '18 at 08:10

All you need to do is print a space (0x20) when you are done and that will overwrite the spinner.

ie: fmt.Fprint("\r \r") to put the cursor back to beginning of line after the space.

This answer is helpful, thank you! But, there is an important detail! Because the spinner function has a delay, it cannot stop exactly when StopSpinner boolean flag is set to true. So, I have added a channel for synchronization.

func Spinner(delay time.Duration) {
    for !StopSpinner {
        for _, r := range `-\|/` {
            fmt.Printf("\r%c", r)
            time.Sleep(delay)
        }
    }
    fmt.Fprint("\r \r")
    c <- struct{}{}
}

Now, calling function waits, while my spinner stop.

var c chan struct{} = make(chan struct{}) // event marker

func callingFunc(){
  StopSpinner = false
  go Spinner(100 * time.Millisecond)

  // do something...
   StopSpinner = true

   <-c // wait spinner stop

   //do something else
}

In my opinion, this is the complete solution!

score 2 · Answer 3 · answered Jan 10 '18 at 16:11

2

fmt.Print("\033[H\033[2J")

This will put the cursor in the top left then clear the console as per this document of useful terminal commands:

https://www.student.cs.uwaterloo.ca/~cs452/terminal.html

answered Jan 10 '18 at 16:11

Iain Duncan

3,139
2
17
28

golang erase symbols from console

3 Answers3