如何使用Go在stdout中将格式化的字符串打印到同一行？

Question

I am iterating over an array and printing a formatted string with each array element to the terminal (stdout). Rather than printing each element on a new line, I want to overwrite the previous output with the program's newest output.

I am using macosx.

I have tried a few ways:

// 'f' is the current element of the array
b := bytes.NewBufferString("")
if err != nil {
    fmt.Printf("Could not retrieve file info for %s
", f)
    b.Reset()
} else {
    fmt.Printf("Retrieved %s
", f)
    b.Reset()
}

A second way was to remove from the string and add and additional Printf before each output: fmt.Printf("\033[0;0H").

Answer 1

You can use the ANSI Escape Codes

First, save the position of the cursor with fmt.Print("\033[s"), then for each line, restore the position and clear the line before printing the line with fmt.Print("\033[u\033[K")

Your code could be:

// before entering the loop
fmt.Print("\033[s") // save the cursor position

for ... {
    ...
    fmt.Print("\033[u\033[K") // restore the cursor position and clear the line
    if err != nil {
        fmt.Printf("Could not retrieve file info for %s
", f)
    } else {
        fmt.Printf("Retrieved %s
", f)
    }
    ...
}

It should work unless your program prints the line at the bottom of the screen, generating a scrolling of your text. In this case, you should remove the and make sure that no line exceeds the screen (or window) width.

Another option could be to move the cursor up after each write:

for ... {
    ...
    fmt.Print("\033[G\033[K") // move the cursor left and clear the line
    if err != nil {
        fmt.Printf("Could not retrieve file info for %s
", f)
    } else {
        fmt.Printf("Retrieved %s
", f)
    }
    fmt.Print("\033[A") // move the cursor up
    ...
}

Again, this works as long as your line fits on the screen/window width.