Question

I have always wondered how people update a previous line in a command line. a great example of this is when using the wget command in linux. It creates an ASCII loading bar of sorts that looks like this:

[======>                    ] 37%

and of course the loading bar moves and the percent changes, But it doesn’t make a new line. I cannot figure out how to do this. Can someone point me in the right direction?

Answer 1

There are two ways I know of to do this:

• Use the backspace escape character (‘\b’) to erase your line
• Use the curses package, if your programming language of choice has bindings for it.

And a Google revealed ANSI Escape Codes, which appear to be a good way. For reference, here is a function in C++ to do this:

void DrawProgressBar(int len, double percent) {   cout << '\x1B[2K'; // Erase the entire current line.   cout << '\x1B[0E'; // Move to the beginning of the current line.   string progress;   for (int i = 0; i < len; ++i) {     if (i < static_cast<int>(len * percent)) {       progress += '=';     } else {       progress += ' ';     }   }   cout << '[' << progress << '] ' << (static_cast<int>(100 * percent)) << '%';   flush(cout); // Required. }