cansi-escape

What does printf("\033[H\033[J") do in C?

I have gone through the below strange sequence of characters in some random website. When compiled and executed, this sequence cleared all previous content in terminal.

Does this clear the stdout buffer or only the tty buffers?

int main()
{
    printf("\033[H\033[J");
    return 0;
}
Solution

  • These are ANSI escape codes.

    \033 stands for ESC (ANSI value 27).

    ESC [ is a kind of escape sequence called Control Sequence Introducer (CSI).

    CSI commands starts with ESC[ followed by zero or more parameters.

    \033[H (ie, ESC[H) and \033[J are CSI codes.

    \033[H moves the cursor to the top left corner of the screen (ie, the first column of the first row in the screen).

    and

    \033[J clears the part of the screen from the cursor to the end of the screen.

    When used in combination, it results in the screen getting cleared with cursor positioned at the beginning of the screen.

    This is the functionality that you get when using Ctrl+L or clear command on bash.

    These CSI can have parameters as well. If none are provided, it will use the default values.