Features›Editing›Repeat character (REP)

Repeat character (REP)

Category: editing · Baseline: modern · Tags: ECMA-48 Standard · Specification ↗

ESC [ N b

REP repeats the preceding graphic character N times. The sequence is ESC [ N b (default N=1). This is a bandwidth optimization — instead of sending the same character hundreds of times (e.g., filling a row with dashes), the application sends the character once followed by REP. Not all terminals implement this sequence.

How this is testedautomated
Write "X" then send \x1b[4b (REP 4), verify 5 consecutive X characters (1 original + 4 repeats).

The same probe runs against headless backends (via Termless) and real terminal apps (via a daemon launched in each terminal). This lets us distinguish parser correctness from rendering correctness.

Analysis2026-04-06

Supported by 11 of 12 terminals (92%). Not supported by: vt100.js. Part of the Modern TUI baseline. Notes: vt100.js: REP not implemented — pure TypeScript emulator.

Supported by 12 of 14 backends (86%)

Terminal Applications

Terminal	Version	Support	Notes
iTerm2	3.6.9	✓ yes
Ghostty	1.3.1	✓ yes
VS Code		✓ yes
Warp		✓ yes
Cursor		✓ yes
Terminal.app		✓ yes

Headless Backends

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

Backend	Version	Support	Notes
Alacritty	0.26.0	✓ yes
Kitty	0.40.0	✓ yes
vterm	0.2.0	✓ yes
WezTerm	0.1.0-fork.5	✓ yes
xterm.js	5.5.0	✓ yes
vt100.js	0.2.1	✗ no	REP not implemented — pure TypeScript emulator

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