Embedding Lua in the Source Engine
Andrew Charles Parker McWatters (andrew@andrewmcwatters.com), 2010
Software Development Manager, Planimeter
What is Lua?
Lua is a powerful, fast, lightweight, embeddable scripting language.
Lua combines simple procedural syntax with powerful data description constructs based on associative arrays and extensible semantics. Lua is dynamically typed, runs by interpreting bytecode for a register-based virtual machine, and has automatic memory management with incremental garbage collection, making it ideal for configuration, scripting, and rapid prototyping.
Find out more about Lua on here.
Overview
Lua is currently the leading scripting language in games, and for Steam users, is synonymous with Garry's Mod. Unfortunately, Garry's Mod isn't open source. However, 
Half-Life 2: Sandbox is currently the leading open source project dedicated to bringing the developer community a method for embedding Lua into their mod nearly seamlessly, and this article will explain how.
Half-Life 2: Sandbox uses a pure variant of Lua, different than Facepunch's implementation of the language, which has restrictions on many libraries, and modified syntax for C++ styled comments. Half-Life 2: Sandbox goal is to provide a neutral, clean, standardized and well documented code base for interfacing with Lua, unlike articles seen within the Valve Developer Community such as the LuaBind oriented Lua tutorial or Adding Lua article.
Implementation
Files
Installation
The Lua manager scripts found in the Half-Life 2: Sandbox source code were written generically so they could be added to any mod.
- While working with a mod's source code, rather than a plugin, the files above should be placed within src/game/shared
- In the project files, place both the luamanager.cpp and luamanager.h in the Source Files filter
- Compile the binaries
- Simply add the precompiled lua51.dll to the mod's bin folder!
Source 2013 Implementation
KYPT1: Make sure your mod uses Git versioning software so we can cherry-pick the commit from OpenMod to your project. (Note this only supports the MultiPlayer & TF2 2013 SDK).
Installation of Git.
On 
Linux You should install it via your package manager (For example on Arch Linux you can run sudo pacman -Syu git). Then in your mod's directory run git init && git add . && git commit -m "Initial Git Commit".
On 
Windows You can install it via the .exe. Simply head to git's website and install it. Once you've done that head to your mod's directory and run git init && git add . && git commit -m "Initial Git Commit"
Installation of Lua.
Once you've set up Git cherrypick the 
https://github.com/ThePixelMoon/OpenMod via the command:
git remote add openmod https://github.com/ThePixelMoon/OpenMod.git && git fetch openmod 1dffddd557c5a1bfeec2a8c2ddad6883b2935b87 && git cherry-pick 1dffddd557c5a1bfeec2a8c2ddad6883b2935b87
Resolve conflicts (if any) and commit the changes using git cherry-pick --continue.