ECH — Erase Character (CSI Pn X)

Used in

Real-world tools that emit this sequence — anchors the bytes to commands you've already used.

• vim / neovim `:redraw!` per-cell repaint—When `'lazyredraw'` is off, vim's screen repaint emits ECH for spans where the new cell content is blank with the same SGR background as the prior row — cheaper than DCH because the line width doesn't change so the right edge doesn't need a redraw pass
• bash readline prompt redraw on history-back—bash readline emits ECH for the prior prompt's trailing width during `Up`-arrow history recall when the new line is the same length, avoiding the `\x1b[K` full-EOL clear cost — visible in `bind -p | grep delete-char` traces and the `READLINE_DEBUG` log
• htop column-cell update—htop redraws CPU / memory bar fills using ECH per cell rather than the whole row — cells whose value didn't change keep their prior render; cells whose value changed get a one-shot ECH+rewrite, keeping the per-frame byte cost proportional to the changed-cell count
• less / more status-line update on file-position change—less ≥ 600 redraws its bottom-line `:` status using ECH for the byte-count and percent-loaded slots when the file scrolls — keeps the status redraw under 30 bytes per keystroke vs ~80 for a `\x1b[K` + full reprint
• terminfo `ech` capability (`ech1` is intentionally absent)—The `ech` cap is parameterised in every modern terminfo entry — there is no `ech1` shortcut because the no-shift semantics make the count argument universally needed; `tput ech 5` resolves to `\x1b[5X` on `xterm-256color` and `tmux-256color`

Related pitfalls

Known footguns this sequence creates in the wild. Each links to the full symptom + cause + fix.

• ⚠ECH with omitted Pn (\x1b[X) defaults to 1 per ECMA-48 §8.3.38 — explicit \x1b[0X is also 1, not zero / no-op·#csi-default-params

Frequently asked

Short answers to the questions developers actually search for this sequence.

What's the difference between ECH (\x1b[5X) and DCH (\x1b[5P)?

ECH (Erase Character — final byte X, 0x58) *overwrites* Pn cells starting at the cursor with SP, leaving the row's overall width unchanged. DCH (Delete Character — final byte P, 0x50) *removes* Pn cells and shifts the trailing row content left by Pn. Pick ECH when you need to clear a fixed-width field (input prompt, table cell, progress-bar segment) without disturbing what's after it; pick DCH when the row content past the cursor should genuinely move left (e.g. a delete-char in a line editor). Both leave the cursor in place; both honour the current SGR background colour for the blanked cells.

Why doesn't \x1b[K (EL) cover what ECH does?

EL (Erase in Line) clears *to end of line*, *from start of line*, or the *whole row* depending on the mode byte (0/1/2) — it has no fixed-width count. ECH clears exactly Pn cells. Use EL when redrawing a prompt and you want any leftover tail ("old prompt was longer than new prompt") gone; use ECH when you have a precise width to wipe without affecting what follows. The common idiom in prompt redrawing is ECH the known-width prefix, then \x1b[K as a tail safety in case the new content is shorter than the previous render.