# Control mode vs one-shot

Source: https://libtmux.org/en/py/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.

<a id="where-each-port-draws-the-line"></a>

## Available transports

Each library call starts a tmux subprocess. [`ControlMode`](<https://libtmux.org/en/py/latest/reference/libtmux-_internal-control_mode-controlmode/>) in
`libtmux._internal` is an internal test helper, not a public command transport.

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

## 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.
Python's internal [`ControlMode`](<https://libtmux.org/en/py/latest/reference/libtmux-_internal-control_mode-controlmode/>) test helper uses this behavior for commands that
require an attached client, such as [`display-popup`](https://libtmux.org/en/tmux/latest/manual/display-popup/) and [`detach-client`](https://libtmux.org/en/tmux/latest/manual/detach-client/).

## 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.

<a id="choosing-a-lane"></a>

## 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.

```python
import libtmux

# One-shot: every call underneath this handle spawns a `tmux` process.
server = libtmux.Server()
session = server.new_session(session_name="work")
session.active_window.active_pane.send_keys("echo hello")
```

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

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