How to print text starting from the top left corner of console on linux?

Question

I want to print some dynamic status text message starting from the top left corner of console, leaving the left area blank on linux(something like watch -n 1 pwd). How can I do it using C or C++?

Answer 1

There is a good chance that your terminal supports ANSI escape codes. These provide a way of altering terminal output properties, controlling cursors, etc.

In the program below ESC is defined to be an escape code prefix, CLS is defined to be the control sequence that clears a screen, and HOME is defined to be the control sequence that moves the cursor to its home position at the top left of the console window. Printing these codes to a terminal window should have the desired effect in terminal emulators that support ANSI escape codes.

Note that this is not supported by the C language, but is widely supported by terminal emulators.

#include <stdio.h>

/* ANSI Escape Sequences */
#define ESC  "\x1B"
#define CLS  ESC"[2J"
#define HOME  ESC"[H"

void clear_to_top(void) {
    printf(CLS);
    printf(HOME);
    fflush(stdout);
}

int main(void) {
    clear_to_top();
    puts("Starting from the top....");
}

Answer 2

You can clear the terminal screen and set the cursor to the top left corner by printing a '\f' byte to the terminal. eg: putchar('\f'), but remember that stdout is line buffered by default so you may need to flush the buffered output with fflush(stdout).

'\f' stands for form feed, a command used to eject the page from the printer, and is interpreted by terminals as a clear screen command.

The byte value in ASCII is 12, also referred to as Ctrl-L.

Some terminals handle it this way, but it seems neither the OP's ConEmu, nor macOS' Terminal or iTerm2, nor most X-Windows terminals... So this is definitely not a solution to the problem.