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.

What programming language is this? It is not bash. Please remove the `bash` tag and add the appropriate tag. This will attract more attention from people who can better answer your question. — Adam Katz, Dec 18 '18 at 17:46
@AdamKatz Actually, I think the same principle applies to other languages, my code is just an example. — McGrady, Dec 19 '18 at 01:37

score 10 · Answer 1 · edited Aug 24 '22 at 16:08

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

score 0 · Answer 2 · answered Dec 14 '18 at 10:21

0

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

with an additional cursor-down (i.e., \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, e.g., cursor-forward (i.e., \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);
}

answered Dec 14 '18 at 10:21

Thomas Dickey

51,086
7
70
105

,let me try it. – McGrady Dec 14 '18 at 11:06
But if the input string is changeable, maybe multiple lines, can I reset the cursor to the end of last line? what about `\033[s` to save cursor position? – McGrady Dec 14 '18 at 11:31
That depends upon the terminal (see [this](https://stackoverflow.com/questions/28986776/ansi-escape-sequence-save-restore-cursor-position-support)). – Thomas Dickey Dec 14 '18 at 22:29

score 0 · Answer 3 · answered Dec 20 '18 at 14:14

0

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

For example:

watch df -h

answered Dec 20 '18 at 14:14

MrMartin

411
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Refresh first N lines and reset cursor to the end of current line with escape sequences?

3 Answers3