Refresh first N lines and reset cursor to the end of current line with escape sequences?

Question

Here's the situation, I want to make some terminal interaction, I want to start child thread to refresh the first N lines, and use the main thread to handle user input.

After that the program will print changeable string, maybe some logs.

The child thread like this:

    let mut count: i32 = 0;
    loop {
        println!("\x1B[2F\x1B[2KHi user1, count:{}\n", count);
        count += 1;
        let ten_millis = time::Duration::from_millis(1000);
        thread::sleep(ten_millis);
    }

e.g.:

----------------
Hi user1, count: 0


Input:  1+1
Output: 2
----------------

The refresher code works well, but the cursor will reset to the start of line, and I want to move it always to the end of the last line. How can I do this trick?

Any help would be great appreciated.

Answer 1

When it boils down to moving the cursor around, you might be interested in simple ANSI escape Sequences:

ANSI escape sequences allow you to move the cursor around the screen at will. This is more useful for full screen user interfaces generated by shell scripts, but can also be used in prompts. The movement escape sequences are as follows:

Description	Sample
Put the cursor at line L and column C	\033[<L>;<C>H
Put the cursor at line L and column C	\033[<L>;<C>f
Move the cursor up N lines	\033[<N>A
Move the cursor down N lines	\033[<N>B
Move the cursor forward N columns	\033[<N>C
Move the cursor backward N columns	\033[<N>D
Clear the screen, move to (0,0)	\033[2J
Erase to end of line	\033[K
Save cursor position	\033[s
Restore cursor position	\033[u

_{source: Bash Prompt HOWTO: Cursor movement}

While these ANSI escape sequences work very nicely, you might, from time to time be interested in the usage of tput as it gives you more readablilty of your scripts. Explaining tput here would be a bit overkill, but the above commands can be done as:

Description	Sample
Put the cursor at line L and column C	tput cup <L> <C>
Move the cursor up N lines	tput cuu <N>
Move the cursor down N lines	tput cud <N>
Move the cursor forward N columns	tput cuf <N>
Move the cursor backward N columns	tput cub <N>
Clear the screen, move to (0,0)	tput clear
Erase to end of line	tput el
Save cursor position	tput sc
Restore cursor position	tput rc

There are many many many other options available. See

• man tput
• man 5 terminfo