刷新前N行并使用转义序列将光标重置到当前行的末尾？

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);
    }

eg:

----------------
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:

• Position the Cursor: \\033[<L>;<C>H or \\033[<L>;<C>f puts the cursor at line L and column C.
• 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:

• Position the Cursor: tput cup <L> <C> puts the cursor at line L and column 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

Answer 2

You could make the child "know" that input is in progress, and in that case, follow the println!

• with an additional cursor-down (ie, \\x1B[B ) or next-line ( \\x1B[E ),
• followed by a movement in that line using the length of the prompt plus the length of the current input, eg, cursor-forward (ie, \\x1B[C with the number of columns as a parameter before the C ).

Something like

if (input_length) {
    cursor_down();
    cursor_forward(prompt_length + input_length);
}

Answer 3

While not quite answering your question, the standard bash way to do this is watch

For example:

watch df -h