Underline (SGR 4)

Category: sgr · Tags: ECMA-48 Standard, VT100 · Specification ↗

ESC [ 4 m

SGR 4 draws a single underline beneath text. The sequence is ESC [ 4 m. One of the original VT100 attributes, universally supported across terminals. Reset with SGR 24.

How this is tested: Send \x1b[4mX, verify the cell has a truthy underline attribute.

Analysis2026-03-26

Supported by all 8 tested terminals — universal adoption. Part of the Core TUI baseline.

Supported by 13 of 13 backends (100%)

Terminal Applications

Terminal	Version	Support	Notes
iTerm2	3.6.9	✓ yes
Ghostty	1.3.1	✓ yes
VS Code	1.112.0	✓ yes
Warp	0.2026.03.18.08.24.03	✓ yes
Cursor	2.6.21	✓ yes
tmux	3.6a	✓ yes
Kitty	0.46.2	✓ yes
Terminal.app	2.15	✓ yes
GNU Screen	5.0.1	✓ yes

Headless Backends

Parser correctness only — a ✓ means the parser accepts the sequence.

Backend	Version	Support	Notes
Alacritty	0.26.0	✓ yes
vt100	0.2.1	✓ yes
vterm	0.2.0	✓ yes
WezTerm	0.1.0-fork.5	✓ yes

← Back to matrix · sgr features