DECDHL / DECDWL / DECSWL — Double-height / double-width lines (ESC # 3 / # 4 / # 5 / # 6)

Byte forms

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

Description

Four C1-class escape sequences with intermediate byte # (0x23) and a digit final byte (3/4/5/6). No CSI, no parameter — just ESC # n. Each affects the current line (where the cursor sits) and persists until overwritten by another ESC # n on that line, scrolled out, or cleared.

- ESC # 3 — DECDHL top half: render this line at double height, displaying the top half of each glyph (so the visible row is twice as tall as a normal row, occupying its own grid row). - ESC # 4 — DECDHL bottom half: same line content as the # 3 line above it, but rendering the bottom half of the doubled glyphs. The convention is to write the same string on two consecutive lines and mark the first # 3 and the second # 4 — the terminal stitches them into one double-height word. - ESC # 5 — DECSWL: Single-Width Line — the default. Use this to explicitly clear a previous # 6 / # 3 / # 4 from the current line. - ESC # 6 — DECDWL: Double-Width Line — each glyph occupies two cell-widths. The line is the same height as a normal row but half as many glyphs fit. Glyphs past the new visible width are clipped (not wrapped).

Why four sequences and not two? The double-height pair (# 3 + # 4) requires the same text on two adjacent rows because the display engine renders the top half from the upper line and the bottom half from the lower line — each line still occupies one grid row, so cursor positioning, scroll math, and erase still work on a one-row-per-byte basis. Double-width (# 6) doesn't need a partner because it doubles only horizontally. Modern emulators that implement these (xterm, mlterm, urxvt, gnome-terminal partial, konsole partial) honour them visually; alacritty / kitty / wezterm / ghostty silent-ignore — they're considered a legacy aesthetic feature with no path forward in graphical-output-rich emulators. Use case today: nostalgia / retrocomputing demos, DECALN-paired alignment tests (ESC # 8, slug decaln), and faithful VT100 ROM emulators. Cursor behaviour: when entering a double-width line, the cursor's logical column 1-40 maps to visual column 1-80; a write past visual column 80 (logical 41) is clipped or wraps depending on DECAWM.

Spec citation: DEC VT100 (DECDHL / DECDWL / DECSWL) / xterm-ctlseqs

Parameters

Examples

# Banner-style double-height header:\nclear\nprintf '\033#3WELCOME\n'   # top half\nprintf '\033#4WELCOME\n'   # bottom half — same text, completes the doubled glyph

import sys\nsys.stdout.write('\x1b#6BIG\n')   # double-width single-height\nsys.stdout.write('\x1b#5normal again\n')   # explicit single-width

// Construct a 2-line splash header:\nfor _, half := range []string{"\x1b#3", "\x1b#4"} {\n    fmt.Print(half + "ANSICODE\n")\n}

process.stdout.write('\x1b#6Wide Title\n')   // double-width\nprocess.stdout.write('\x1b#5')               // reset line to normal width

printf("\x1b#3SPLASH\n");   /* top */\nprintf("\x1b#4SPLASH\n");   /* bottom — terminal stitches into doubled glyphs */

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

yes

GNU screen

yes

Related sequences

• DECALN — Screen alignment pattern (ESC # 8)
• DECSTR — Soft terminal reset
• RIS — Reset to Initial State (full terminal reset)
• DECCOLM — 80 / 132 column mode (CSI ? 3 h / l)

In the family cookbook

↗ESC cookbook · 4. Double-width / double-height lines + alignment test — `\x1b#3-#6` and `\x1b#8`