The Three Building Blocks of a Script

Every script, no matter how complex, is built from three fundamental concepts.

States

A state is a mode of behavior. An object can be in an "on" state or an "off" state. A door can be "open" or "closed." Every script starts in the `default` state.

Events

Events are triggers. When someone touches an object (`touch_start`), a timer goes off (`timer`), or the object collides with something (`collision`), an event runs.

Functions

Functions are the actions. `llSay()` makes an object talk. `llSetColor()` changes its color. `llDie()` deletes the object. You use functions inside events to make things happen.

Example 1: The Classic "Hello, World!"

This is the traditional first step in any programming language. We'll make a prim say "Hello, World!" when you touch it.

Create a prim (Right-Click ground > Create).
In the Edit window, go to the `Content` tab.
Click `New Script`, delete the default text, and paste this in:

default
{
    touch_start(integer total_number)
    {
        llSay(0, "Hello, World!");
    }
}

What's Happening Here?

default { ... }: The script begins in its one and only state, the `default` state.
touch_start(...) { ... }: This defines the `touch_start` event. The code inside these curly braces `{}` will only run when someone clicks the object.
llSay(0, "Hello, World!");: This is the function that does the work. It tells the object to say "Hello, World!" in public chat.

Example 2: A Simple Light Switch

Let's make something more useful. This script will make a prim toggle between white ("on") and black ("off") when touched. This will teach you how to use multiple states and store information in a variable.

// Define colors to use later. This part is outside of any state.
vector COLOR_ON = <1.0, 1.0, 1.0>;  // White
vector COLOR_OFF = <0.0, 0.0, 0.0>; // Black

default // This will be our "ON" state
{
    state_entry()
    {
        llSay(0, "Light is now ON.");
        llSetColor(COLOR_ON, ALL_SIDES); // Set the color to white
    }

    touch_start(integer total_number)
    {
        state off; // When touched, switch to the 'off' state
    }
}

state off
{
    state_entry()
    {
        llSay(0, "Light is now OFF.");
        llSetColor(COLOR_OFF, ALL_SIDES); // Set the color to black
    }

    touch_start(integer total_number)
    {
        state default; // When touched, switch back to the 'default' (ON) state
    }
}

New Concepts in This Script:

Variables: `vector COLOR_ON` and `vector COLOR_OFF` are variables. We store the color values in them at the top so we can easily reuse them later.
`state_entry()` Event: This event runs automatically *as soon as* the script enters a new state. It's perfect for setting things up, like changing the color.
`llSetColor()` Function: This function changes the color of the prim.
`state off;` Command: This is how you tell the script to jump from the `default` state to the `state off`. The script then stops listening to events in `default` and starts listening to events in `off`.

Where to Go From Here?

You've learned the most important concepts! The best way to learn now is to experiment.

Modify the Code: Try changing the colors in the light switch script. Make it change to red or blue! Try changing the messages in `llSay`.
Explore Other Events: Look up other simple events like `listen()` to make an object respond to chat commands.
Visit the LSL Wiki: The official Second Life LSL Wiki is the ultimate reference for all events and functions. If you want to know what a function does, search for it there.

Suggestions for New Content and Images

To Make This Guide Even Better:

`lsl-new-script.jpg`: A screenshot of the `Content` tab in the edit window, with an arrow pointing to the `New Script` button.
`lsl-editor.jpg`: A screenshot of the LSL script editor window that opens, showing the default "Hello World" script inside.
Create an Advanced Scripting Guide: The bouncing ball example from the original guide was too advanced for an intro. Create a separate `howto/11-advanced-lsl-physics.php` guide for it. That's a perfect place for complex topics like physics, vectors, and collisions.

Intro to LSL Scripting