How do I determine size of ANSI terminal?

Question

Standard input and output are connected to a terminal that implements ANSI escape sequences, but is of unknown dimensions.

I need to know how big the terminal so to facilitate drawing a full-screen text UI on it. How can I get the size?

The correct size is not loaded into environment variables. I cannot use TIOCGETS; the the call would return success but the values are not correct -- the kernel doesn't know the size either.

There are lots and lots of answers searching stackoverflow, but they all depend on the OS providing the answer one way or anther; but this time that is not true.

The best clue I can find is the DSR command which returns the current cursor position; but there's no move to bottom/right command.

https://www.gnu.org/software/termutils/manual/termcap-1.3/html_mono/termcap.html#SEC25 :: "co" and "li" — wildplasser, Feb 28 '16 at 21:19
Ok, Ok. I stand corrected. Let's assume 80*24 then, for crippled terminals (and maybe allow an override using command line flags on the client side) — wildplasser, Feb 28 '16 at 22:08
OP needs clarification on ANSI sequences; `resize` is a good example for starting that, since it does what OP actually needs to know. — Thomas Dickey, Feb 28 '16 at 22:22

Thomas Dickey · Accepted Answer · 2016-02-28T22:26:41.677

The resize program does this by moving the cursor to a very large column and row; the terminal moves as far as it can, e.g.,

CUP 999 999

Then resize asks where the cursor is:

DSR 6

The terminal replies with the actual cursor position (i.e., the cursor position report CPR), from which resize knows the terminal's size: the cursor is on the lower-right corner.

That's all done using standard (ECMA-48 / VT100) escape sequences. In XTerm Control Sequences (which should apply to your "ANSI" terminal)

CSI Ps n  Device Status Report (DSR).
            Ps = 6  -> Report Cursor Position (CPR) [row;column].
          Result is CSI r ; c R

How do I determine size of ANSI terminal?

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