> For the complete documentation index, see [llms.txt](https://luadoc.edgetx.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://luadoc.edgetx.org/2.9/part_i_-_script_type_overview/function_scripts.md).

# Function Scripts

## Overview

Function scripts are invoked via the **'Lua Script'** option of Special Functions configuration page.

Typical uses of Function scripts are:

* specialized handling in response to switch position changes
* customized announcements

Please be aware that:

* all function scripts are stopped if a One-Time Lua script is running
* Function scripts **DO NOT HAVE ACCESS TO LCD DISPLAY**

## Lifetime

* `init` function is called once when the model is selected
* depending on the switch associated with the Special Function, either the `run` function (switch = on) or the `background` function (switch = off) is called periodically
* the script is stopped and disabled if it misbehaves (e.g. run-time error or low memory)

## File Location

Scripts are located on the SD card in the folder /SCRIPTS/FUNCTIONS/<*name*>.lua. File name length (without extension) **must be 6 characters or less** (this limit was 8 characters in OpenTX 2.1).

## Interface

Every script must include a `return` statement at the end, defining its interface to EdgeTX. This statement returns a table with the following fields:

* `init` function (optional)
* `run` function
* `background` function (optional)

### Example

```lua
local function init()
  -- Called once when the script is loaded
end

local function run()
  -- Called periodically while the Special Function switch is on
end

local function background()
  -- Called periodically while the Special Function switch is off
end

return { run=run, background=background, init=init }
```


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