# Control mode vs one-shot

Source: https://libtmux.org/en/ts/latest/concepts/transports/

> Choose subprocesses, command batches, or persistent connections to send commands and receive events.

libtmux sends commands to tmux through subprocesses or persistent control-mode
connections. tmux also accepts several commands in one invocation:

1. **One-shot subprocess.** Each command spawns a fresh `tmux` process,
   which sends the request to the server, prints the result, and exits.
2. **A persistent control-mode client.** [`tmux -C attach-session`](https://libtmux.org/en/tmux/latest/manual/attach-session/) starts one
   long-lived tmux process that stays attached and speaks a line-oriented
   protocol over its stdout: commands go in, replies and asynchronous
   notifications (`%window-add`, `%output`, ...) come out, without starting a
   process per call.
3. **One invocation, several commands.** tmux accepts more than one command
   per invocation (`;`-joined, or one `-F`-tagged `list-*` per line). Grouping
   operations this way reduces process starts without opening a control-mode
   connection.

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## Available transports

Commands use a subprocess by default. [`pipeline()`](<https://libtmux.org/en/ts/latest/reference/server-server-pipeline/>) and [`batch()`](<https://libtmux.org/en/ts/latest/reference/server-server-batch/>) group
operations. [`connect()`](<https://libtmux.org/en/ts/latest/reference/server-server-connect/>) and [`watch()`](<https://libtmux.org/en/ts/latest/reference/server-server-watch/>) keep a connection for notifications;
ordinary commands still use separate processes.

Choose based on whether you need command results, notifications, or a batch of
changes.

## Notifications and commands are separable

TypeScript's [`connect()`](<https://libtmux.org/en/ts/latest/reference/server-server-connect/>) adds an event observer while commands such as
[`session.newWindow(...)`](<https://libtmux.org/en/ts/latest/reference/session-session-newwindow/>) and [`pane.sendKeys(...)`](<https://libtmux.org/en/ts/latest/reference/pane-pane-sendkeys/>) continue to run as separate
tmux processes. A dedicated process provides a completion boundary for output
from alias-expanded or waiting commands.

## A control client is a real client

A persistent control connection attaches a tmux client. It appears in
[`list-clients`](https://libtmux.org/en/tmux/latest/manual/list-clients/), increments [`session_attached`](https://libtmux.org/en/tmux/latest/catalog/formats/session_attached/), and affects [`destroy-unattached`](https://libtmux.org/en/tmux/latest/catalog/options/destroy-unattached/),
client hooks, and idle-client accounting. Each connection counts separately.

## Why fold several commands into one invocation

Creating an object can require a second command to read its resulting state.
Batching can reduce repeated reads and process starts.

[`batch()`](<https://libtmux.org/en/ts/latest/reference/server-server-batch/>) resolves planned mutations from one final snapshot.

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## What this costs in practice

A persistent connection avoids starting a client for each command. A chain
groups a known sequence into one invocation. For occasional commands, use the
default subprocess transport; measure your workload before changing transports
for performance. Use a notification stream when your program needs tmux events.

## Sending a command

The example uses the subprocess API. See the reference for batching and
control-mode setup.

```typescript
import { Server } from "libtmux";

// Each awaited command uses a tmux subprocess.
const server = new Server();
const session = await server.newSession({ name: "work" });
const editor = await session.newWindow({ name: "editor" });
await editor.panes.at(0)?.sendKeys("echo hello");
```

To inspect tmux's control protocol, attach a control client:

```console
$ tmux -C attach-session -t work
```