> For the complete documentation index, see [llms.txt](https://documentation.hak5.org/packet-squirrel-mark-ii/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://documentation.hak5.org/packet-squirrel-mark-ii/advanced-payloads/background-commands.md).

# Background commands

## Running commands in the background

Normally, commands in a payload are run until they complete, then the next command runs.  This blocks the rest of the payload from executing while a long-running command runs.

Often this is desirable:  This functionality is what allows a payload to pause until a button is pressed, for instance.

At other times, a payload may need a command to run in the background; to run multiple `KILLSTREAM` commands with different patterns, monitor status of a command, or for other reasons.

To solve this, commands can be run concurrently, called "backgrounding".  Any number of commands or functions can be run in the background at once; when backgrounded, the payload immediately executes the next command.

Appending an `&` to the end of a command tells Bash to run this command in the background.

To run multiple commands, simply run all of them with an `&` after each:

```bash
#!/bin/bash 

# Title: Killstream multi example
#
# Description: Kill multiple types of streams

NETMODE BRIDGE
LED R SINGLE


KILLSTREAM br-lan ANY 'Authorization: Basic' 80 &
KILLSTREAM br-lan ANY 'Foobar' 80 &
KILLSTREAM br-lan ANY '[0-9}{3}-[0-9]{2}-[0-9]{4}' 80 &

wait
```

All the commands will be run, regardless if the commands are successful.

### Waiting for commands

In the example above, the `wait` command is used.  This keeps the payload running until all backgrounded commands have finished.

Without the `wait` command, the payload above would run the `KILLSTREAM` command, but then immediately complete:  Backgrounded commands will not keep a payload running!

Using the `wait` command tells the payload to continue running.  In this case, it will run indefinitely, as the `KILLSTREAM` command runs forever.

## Running groups of commands in the background

A group of commands can be made using the `{` and `}` symbols, and run in the background.

This can easily be combined with the `while true` loop to run forever, and something like the `BUTTON` command to wait for user input, for example:

```bash
#!/bin/bash

# Title: Button blinky
# 
# Description: Blink the LED whenever the button is pressed

NETMODE NAT

# Group the commands inside {} and run them in the background with &
{
    # Repeat forever
    while true; do
        # Wait for the button
        BUTTON
        
        # Set the LED to blue
        LED B SOLID
        
        # Wait a second
        sleep 1
    done
} &

# Do whatever else in the payload here

wait
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://documentation.hak5.org/packet-squirrel-mark-ii/advanced-payloads/background-commands.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.