# 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.

## 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>.