---
name: pardes-9p
description: Inspect and drive a running Pardes editor through its virtual filesystem (served over 9P), or exercise its panes, builtins, terminal input and rendered output in an isolated session. Use for Pardes interaction, plugin development and end-to-end debugging.
---

# Pardes over 9P

Pardes is files: `cat`, `echo >`, `ls` and shell scripts are the whole
interface. The recipes are in the Scripting chapter
([docs/typ/scripting.typ](../../../docs/typ/scripting.typ)), every file's
semantics in the Reference chapter
([docs/typ/reference.typ](../../../docs/typ/reference.typ)), and a running
session serves a summary at `$m/README`. Paths are relative to the
repository root.

## Find the session

```sh
m=${PARDES_MOUNT:-}
[ -n "$m" ] || echo 'no mount: use 9p -a "unix!$PARDES_9P" read index'
cat "$m/index"
```

Under `9ns --mntgen` every pane gets `$PARDES_MOUNT`, its session as a
directory (also in a `Tty9p` shell). `$PARDES_9P` is the session socket of
the pane you run in, `$PARDES_PANE` that pane's serial. A dead session's
entry answers `Input/output error`: name the session, never glob. Without a
mount, plan9port's `9p -a "unix!$PARDES_9P"` works, and `test/ninep.py` in the source tree (Reference, "Other ways in").

## Traps

- A refused write says only `Invalid argument` or `Input/output error`;
  `grep '^err' $m/log | tail -1` says why. Not the log's last line: after
  a refused Del, Exit or Restore that may be `+Unsaved`'s `new`.
- Work through a pane of your own (`n=$(cat $m/pane/new)`) and its own
  `look` and `exec`: the root's act at the pane with the keyboard, which another
  client, an idle shell or an event helper may own.
- `head` on `index`, `layout`, `log` or `recent` through 9ns says `Illegal
  seek`: use `sed -n 1p`. In `index`, `term` is a shell, `cmd` a command's
  pane.
- `addr` is the pane's and moves on: each `/re/` searches from the last
  address, and a `data` write leaves it just past the text. Write `addr`
  before each replacement; a failed address leaves none.
- An Edit `x` that matches nothing succeeds: check the text afterwards.
- Each open of `pane/new` makes a pane: read it once.
- Through a mount, `printf 'a\nb\n' > ctl` arrives one write per line: send
  a block as one write (`cat block > $p/ctl`), ending in a newline.
- Pane words (`Save`, `Undo`, `Del`) go to `pane/<n>/ctl`, settings and
  session words to `$m/ctl`.
- `Exit`, `Restore`, `Del` and `get` refuse once over unsaved text.
- Never experiment on a session someone is using: strip every `PARDES_*`
  variable and start your own (Scripting, "An isolated session"); build
  with `-Dplatform=tty`, since a bare `zig build` installs over
  `~/.local/bin`.