A forgotten terminal trick: the host-writable status line.

The VT102 (1978) and VT220 (1983) had the familiar 24-line terminal screen 1. This the reason your terminal defaults to 80×24, or 132×24. The VT320 (1987) kept a 24-line main display for compatibility, but added something extra: a 25th line at the bottom, reserved for status information. That extra line could be hidden, used by the terminal itself, or made writable by the host. In its normal “indicator” mode, the terminal used it for local state: cursor position, printer status, modem status, and similar information. But in host-writable mode, software on the host side of the terminal connection could write directly to that line. 2 The two relevant control sequences are DECSSDT and DECSASD. 3 # Make the status line host-writable printf '\e[2$~' # Send subsequent output to the status line printf '\e[1$}Build running…' # Return subsequent output to the main display printf '\e[0$}' DECSSDT selects the status-display type: CSI 0 $ ~ no status line CSI 1 $ ~ indicator status line CSI 2 $ ~…