> 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/overview/script-types/function-scripts.md).

# Function Scripts

## Purpose

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

Typical uses of Function scripts are:

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

## Execution & Lifetime

Function script is loded when model is selected.\
\
Script executes until

* it misbehaves (e.g. run-time error or low memory)
* [One-time Script](/overview/script-types/one-time-scripts.md) is running. When One-time script finishes execution, Wigdet Script resumes execution.

{% hint style="warning" %}
Function scripts **DO NOT HAVE ACCESS TO LCD DISPLAY**
{% endhint %}

## File Location

Function scripts are located on the SD card in the folder /SCRIPTS/FUNCTIONS/

{% hint style="warning" %}
File name length (without extension) **must be 6 characters or less**
{% endhint %}

## Interface

Every Function script must include a `return` statement at the end, defining its interface to EdgeTX.

This statement returns a table with the following fields:

<table><thead><tr><th width="142.33333333333331">Field</th><th width="108">Type</th><th width="105" data-type="checkbox">Required</th><th>Desctiption</th></tr></thead><tbody><tr><td><strong>run</strong></td><td>function</td><td>true</td><td>This function is called periodicaly when <strong>switch</strong> assiociated the Special Function <strong>is ON</strong>.</td></tr></tbody></table>

*Parameters*\
\&#xNAN;*none*

*Return values*\
\&#xNAN;*none*

<table><thead><tr><th width="142.33333333333331">Field</th><th width="108">Type</th><th width="105" data-type="checkbox">Required</th><th>Desctiption</th></tr></thead><tbody><tr><td><strong>init</strong></td><td>function</td><td>false</td><td>This function is called once when Function script is loaded and executed for the first time</td></tr></tbody></table>

*Parameters*\
none

*Return Values*\
none

<table><thead><tr><th width="142.33333333333331">Field</th><th width="108">Type</th><th width="105" data-type="checkbox">Required</th><th>Desctiption</th></tr></thead><tbody><tr><td><strong>background</strong></td><td>function</td><td>true</td><td>This function is called periodicaly when <strong>switch</strong> assiociated the Special Function <strong>is OFF</strong></td></tr></tbody></table>

*Parameters*\
none

*Return Values*\
none\\

### Example

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

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

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

return { run = my_run, background = my_background, init = my_init }
```


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