DECCOLM — 80 / 132 column mode (CSI ? 3 h / l)

Byte forms

Every common string-literal form so you can paste-and-search either direction.

Description

Column Mode (DECCOLM, private mode 3). Set (`\x1b[?3h`) requests 132-column page width; reset (`\x1b[?3l`, the typical default) returns to 80 columns. Originally a hardware feature of the DEC VT100 — flipping this triggered a real font / clock-rate switch that physically narrowed each character cell so 132 glyphs fit on the same CRT. Software emulators implement it by resizing the page buffer; the side effects are the same as DECSCPP and intentional: - **Screen cleared** to current SGR background. - **Cursor homed** to (1, 1). - **DECSTBM and DECSLRM reset** to full-page. - Any pending **DECOM** (origin mode) state preserved but margins re-anchored. Why the resource gate? In the X11 / VT100 era, applications would emit `?3h` programmatically to gain wide-display real estate, surprising the user by clearing their buffer. Modern emulators (xterm `allowC132`, putty `disable_remote_resize`, others by default) suppress DECCOLM unless explicitly opted in. Result: a program that ships `?3h` today gets silent no-ops on alacritty / kitty / wezterm / ghostty / Windows Terminal — the safe assumption is that DECCOLM does nothing unless you've already verified it works in the target environment. Use DECCOLM (or its parameter-bearing cousin DECSCPP) only when you control the terminal config; otherwise emit a `resize`-style request through your platform's window-management protocol (e.g. ioctl `TIOCSWINSZ`). DECCOLM **persists** until reset or until DECSTR (soft reset returns it to default) or RIS (hard reset).

Spec citation: DEC VT100 (DECCOLM) / xterm-ctlseqs

Parameters

Examples

# Probe and request 132-col, fall back gracefully:\nprintf '\033[?3h'   # request wide\nprintf '\033[6n'    # cursor position report\nIFS='[;R' read -t 0.05 -rsd R _ rows cols < /dev/tty || true\nif [ "$cols" -lt 100 ]; then echo "emulator ignored DECCOLM"; fi

import sys, os\nsys.stdout.write('\x1b[?3h')   # ask for 132\nsys.stdout.flush()\nrows, cols = os.get_terminal_size()\nif cols < 100:\n    print('DECCOLM not honoured — staying narrow')

fmt.Print("\x1b[?3h")\ndefer fmt.Print("\x1b[?3l")   // always restore — clears screen on transition

process.stdout.write('\x1b[?3l')   // explicit 80-col (default; harmless on emulators that ignore DECCOLM)

printf("\x1b[?3h");   /* request 132 cols */\n/* WARNING: screen now cleared. Re-render entire UI. */

Terminal support

xterm

yes

Linux console (fbcon)

no

macOS Terminal.app

partial

iTerm2

partial

Windows Terminal

no

cmd.exe / ConPTY

no

kitty

no

alacritty

no

WezTerm

no

Ghostty

no

GNOME Terminal

partial

Konsole

partial

tmux

no

GNU screen

no

Related sequences

• DECSCPP — Select columns per page (CSI Pn $ |)
• DECSTBM — Set Top/Bottom Margins (CSI r)
• DECSLRM — Set left and right margins (CSI Pl ; Pr s)
• DECSTR — Soft terminal reset
• RIS — Reset to Initial State (full terminal reset)