SGR 4 — Underline

Render following text with an underline.

Byte forms

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

\\x1b[\x1b[4m

\\033[\033[4m

\\e[\e[4m

ESC [ESC [ 4 m

hex1b 5b 34 6d

Description

Single underline. Kitty introduced extensions for styled underlines: `\x1b[4:1m` (single), `4:2m` (double), `4:3m` (curly), `4:4m` (dotted), `4:5m` (dashed); colored underline via `\x1b[58;5;Nm` or `\x1b[58;2;R;G;Bm`. Disable underline with `\x1b[24m`. The double-underline pattern `\x1b[21m` is recognized by xterm and most modern terminals (originally SGR 21 meant 'doubly underlined' in ECMA-48; some terminals interpret it as 'bold off').

Spec citation: ECMA-48 §8.3.117 (SGR parameter 4); kitty underline extensions

Examples

bash

printf '\033[4munderline\033[24m back\033[0m\n'

python

print('\x1b[4munderline\x1b[0m')

fmt.Print("\x1b[4munderline\x1b[0m")

javascript

console.log('\x1b[4munderline\x1b[0m')

printf("\x1b[4munderline\x1b[0m\n");

Terminal support

xterm: yes
Linux console (fbcon): yes
macOS Terminal.app: yes
iTerm2: yes
Windows Terminal: yes
cmd.exe / ConPTY: partial
kitty: yes
alacritty: yes
WezTerm: yes
Ghostty: yes
GNOME Terminal: yes
Konsole: yes
tmux: no
GNU screen: no

xterm	Linux console (fbcon)	macOS Terminal.app	iTerm2	Windows Terminal	cmd.exe / ConPTY	kitty	alacritty	WezTerm	Ghostty	GNOME Terminal	Konsole	tmux	GNU screen
yes	yes	yes	yes	yes	partial	yes	yes	yes	yes	yes	yes	no	no

Related sequences

In the family cookbook

SGR cookbook · 6. SGR colon sub-params — the standards-correct form