Scripting Documentation

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About OpenSimulator scripting

An important ingredient in virtual worlds simulation is scripting.
Scripts allow the addition of actions to 'entities' in world, like making a door react to a touch and open.
Since version, you can chose between old XEngine or new YEngine script engines.
Script engines do script compilation and control script execution.
OpenSimulator script language supports a subset of the Linden Labs Second Life script language (LSL) plus its own extensions (OSSL).

LSL in a nutshell

LSL is a event-driven language. A script is a collection of functions called event handlers.

Events are generated by the environment (mouse clicks, collisions and many more). Many of those events happen at time critical moments, so those event handlers should be small and fast to reduce impact on the rest of simulation. YEngine may allow long processing to happen with less impact on the simulation, but that will happen at lower priority.

(Hopefully), a script does nothing when there is no event to process. Is sits waiting for an event. Only events matching a event handler present in the script will be generated. If the script has no handler for mouse clicks, mouse clicks won't be reported.

LSL functions may also generate events. For example, llRezObject will trigger a object_rez event. llMessageLinked, a link_message event. This makes your script asynchronous (request action in a handler, get result in another handler). Understanding the flow of events in your script is essential.

An event cannot interrupt another event. Processing of the previous event must be finished before accepting a new one. Events are queued up to the number of 300 (OpenSim.ini, MaxScriptEventQueue). Finally, LSL has states that implements the concept of state machine. A script can respond differently to a same event in different states, or to another set of events.

String type in OpenSimulator

Most OpenSimulator LSL/OSSL string functions are only safe with characters that can be represented by a single .net (UTF-16) char. This means strings with characters of the Basic Multilingual Plane excluding combining characters
That is Unicode code points up to U+FFF0, except:

  • U+0300..U+036F (combining characters)
  • U+1AB0..U+1AFF (combining characters)
  • U+1DC0..U+1DFF (combining characters)
  • U+20D0..U+20FF (combining characters)
  • U+D800..U+DFFF (reserved for higher planes encode using 2 chars)
  • U+FE20..U+FE2F

Only in this case some compatibility with SL is possible.
OpenSimulator strings are internally encoded as .net strings that are basically arrays of UTF-16 chars.
A unicode character may be represented by more than one of those chars, but most .net and mono string functions ignore this and just assume all characters are single utf16 chars.
For example llStringLength returns the number of .net chars on the string, not necessary the real number of its characters.
Functions that take a index or in string position arguments use them as a index to the array of chars and so that may point to the middle of a complex character. In this case some of this functions may even create strings with invalid characters.
SL string functions do support most cases of 2 char characters, so full compatibility is not possible without breaking compatibility with older OpenSimulator versions. Only in this case some compatibility with SL is possible. Multiple char characters support also has a high performance cost.

LSL (Linden Scripting Language)
OSSL (OpenSimulator Scripting Language)

Configuring scripting

There are a number of parameters that can be tweaked for scripting, such as those which enable OSSL commands or increase the limits on certain script facilities (e.g. listeners).

For standalone and small grid use, the default scripting settings should be fine. See Configuring Scripting for information on configuring these parameters.

How to use scripts in OpenSimulator

If you have never written a script in LSL before, then please have a look at the LSL wiki to learn the scripting basics. If you do have (some) experience with writing or editing LSL scripts, then the procedure is identical to the procedure on SL. Known problems:

  • Error messages about scripting errors are often cryptic, and tend to be long.
  • Script syntax and execution may depend on the engine used, old XEngine or YEngine
  • On teleports or crossings from a region using YEngine to a region using XEngine, script state (like changed values on global variables) is lost. Should be okay on the inverse direction.

Scripting System Status

Status Tables / Charts related to LSL and OSSL functions, constants and related material.

LSL/OSSL Status Overview


Additional Resources for Scripting (LSL)

There have been many questions regarding scripts and tools for scripting lately. Presented here are a variety of Links to Resources which will help most people with Scripting LSL.

OpenSimulator Specific Materials:

Suggested Links for LSL wikis:

Note the Tutorials, Examples & Script Libraries

Off-World Local LSL Editing Tools & Syntax Highlighters

Note: most do not support osFunctions

All EDITORS (no osFunctions) Windows version availableMacOSX version availableLinux version available

In this repository you can find the syntax grammar, syntax highlighting and snippet files for the Linden Scripting Language (LSL) of Second Life for different kinds of software.

LSL EDITOR (no osFunctions) Windows version available

Now an Open Source project. New release is February 2012 (Ver.2.44.2). A valuable tool and easy install.

LSL Plus (no osFunctions) Windows version availableMacOSX version availableLinux version available

Open source Eclipse plugin. Regular updates. Not quite as quick to get installed as LSLEditor, but very good tool.

Notepad++ (osFunctions supported with add-on UDF) Windows version available

Windows only Editor with enhanced capabilities & supports most languages. Very powerful & feature rich.

KATE (no osFunctions) Windows version availableMacOSX version availableLinux version available

Free and open source text editor, supporting lots of scriptinmg and programming languages out of the box. This includes LSL.

Sublime Text 2 (os*/wl*/mod* functions supported with the bundle below) Windows version availableMacOSX version availableLinux version available

Completions & syntax coloring of LSL/OSSL functions/events/constants & in-world editor look-and-feel theme.
To use OSSL feature, use ".ossl" for your script file extension.
It is currently compatible with LL v3.4.1 and OpenSimulator v0.7.4+ (master r/21068).

More editors are listed at


Additional Resources for Scripting (OSSL)

There have been many questions regarding scripts and tools for scripting lately. Presented here are a a few links to Resources which will help most people with OSSL scripting.

How to contribute

The ScriptEngine is being developed by many developers. New developers are always welcome. If you want to contribute, even just a tiny little bit, have a look at the OpenSim.Region.ScriptEngine page. There is a lot of developer activity on IRC (Support), feel free to drop in.

Example LSL Scripts

See Also