# Prompt Start (OSC 9 ; 12)

> Mark where the shell's prompt starts, the ConEmu way.

- **Sequence:** `OSC 9 ; 12 ST`
- **ECMA-48:** [§8.3.89 OSC – Operating System Command, p. 51](https://archive.org/details/ecma-48-5th-edition-june-1991/page/n64/mode/1up)
- **Specification:** [ConEmu specific OSC, ConEmu's ANSI escape codes](https://conemu.github.io/en/AnsiEscapeCodes.html#ConEmu_specific_OSC)

`OSC 9 ; 12 ST` tells the terminal that the prompt starts at the cursor, so
that it can find the prompts in what scrolled by. A shell sends it from its
prompt string. It does the job of the `A` mark of
[OSC 133](https://control-codes.page/osc/prompt/index.html.md).

It is one of the commands ConEmu, a Windows terminal, put under `OSC 9`; the
[progress report](https://control-codes.page/osc/progress/index.html.md) page lists them all, and their definition
is the [ConEmu specific OSC](https://conemu.github.io/en/AnsiEscapeCodes.html#ConEmu_specific_OSC) table in ConEmu's documentation.
iTerm2 uses `OSC 9 ; text ST` for a [notification](https://control-codes.page/osc/notify/index.html.md), and a
terminal that has both tells them apart by what follows the `9`.

A default xterm ignores all of `OSC 9`, which is not among [the OSC numbers it knows](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/misc.c#L3476-L3504).

libghostty-vt marks the prompt, as it does for OSC 133, so the case is a
known difference.

## Support

| Terminal | Version | Support | Notes |
| --- | --- | --- | --- |
| VT220 | [manual](https://vt100.net/docs/vt220-rm/), 2nd ed., 1984 | No | OSC is not among the controls it recognizes ([§4.2](https://vt100.net/docs/vt220-rm/chapter4.html#S4.2)) |
| VT510 | [manual](https://vt100.net/docs/vt510-rm/), 1st ed., 1993 | No | ignores an OSC string ([chapter 4](https://vt100.net/docs/vt510-rm/chapter4.html)) |
| xterm | patch 412, [xterm-411a](https://github.com/ThomasDickey/xterm-snapshots/tree/xterm-411a) | No | `OSC 9` is not among the OSC numbers it knows |
| libghostty-vt | [0f171f6](https://github.com/ghostty-org/ghostty/tree/0f171f650a1cbbd6df4a2573b6b0c7de57cc6d90) | Yes | CONEMU12-1: marks the prompt start, as for OSC 133 |
| Konsole | 26.11.70, [a24c3d71](https://invent.kde.org/utilities/konsole/-/tree/a24c3d71be3684f24d030aa2dbe9bd723d985233) | No | only `OSC 9 ; 4`, the progress report, is acted on |
| ConEmu | build 230724, its [documentation](https://conemu.github.io/en/AnsiEscapeCodes.html) | Yes | [ConEmu specific OSC](https://conemu.github.io/en/AnsiEscapeCodes.html#ConEmu_specific_OSC) |

## Validation

### CONEMU12-1: The start of a prompt

*A known difference: libghostty-vt does not pass this case.*

Input, one step per line:

```text
\e]9;12\a
$
```

Expected screen:

```text
|$_____|
attr 1,1 semantic=output
```

---

This is the Markdown version of <https://control-codes.page/osc/conemu-prompt/>. On that page every validation case runs live in libghostty-vt, the terminal emulation core of Ghostty, compiled to WebAssembly.

The validation cases are written in the notation described in <https://control-codes.page/notation/index.html.md>.