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using_luarocks.md

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Using LuaRocks

So, you have followed the installation instructions (either on Unix or Windows) and now you have LuaRocks installed on your machine. Now you probably want to install some rocks (packages containing Lua modules) and use them in your Lua code.

For LuaRocks to function properly, we have a quick checklist to go through first:

Command-line tools (and the system path)

LuaRocks installs some command-line tools which are your interface for managing your rocks: luarocks and luarocks-admin. Make sure the directory where they are located is in your PATH -- the exact location depends on the flags you gave when installing LuaRocks.

Run luarocks to see the available commands:

luarocks

You can get help on any command by using the luarocks help command:

luarocks help install

Installing packages is done by typing commands such as:

luarocks install dkjson

Rocks trees and the Lua libraries path

When you install rocks using the luarocks install, you get new modules available for loading via require() from Lua. For example, after we install the dkjson rock, type luarocks show dkjson to show the module installed by the rock:

luarocks show dkjson

This should output something like this:

dkjson 2.5-2 - David Kolf's JSON module for Lua
  
dkjson is a module for encoding and decoding JSON data. It supports UTF-8.
  
JSON (JavaScript Object Notation) is a format for serializing data based on the
syntax for JavaScript data structures.
  
dkjson is written in Lua without any dependencies, but when LPeg is available
dkjson uses it to speed up decoding.
  
License: 	MIT/X11
Homepage: 	http://dkolf.de/src/dkjson-lua.fsl/
Installed in: 	/usr/local
  
Modules:
	dkjson (/usr/local/share/lua/5.3/dkjson.lua)

It presents a short description of the rock, its license, and the list of modules it provides (in this case, only one, dkjson). Note that "Installed in:" shows the directory tree where the rock was installed. This is the "rocks tree" in use.

Most LuaRocks installations will feature two rocks trees:

To be able to use the module, we need to make sure that Lua can find that dkjson.lua file when we run require("dkjson"). You can check your Lua paths from the Lua environment, using

print(package.path)
print(package.cpath)

These variables can be pre-configured from outside Lua, using the LUA_PATH and LUA_CPATH environment variables.

If you installed both Lua and LuaRocks in their default directories (/usr/local on Linux and Mac OSX), then the "system" tree is /usr/local and it will work by default. However, the "user" tree (for installing rocks without admin privileges) is not detected by Lua by default. For that we'll need to configure these environment variables.

LuaRocks offers a semi-automated way to do this. If you type the following command:

luarocks path --bin

...it will print commands suitable for your platform for setting up your environment. On typical Unix terminal environments, you can type this:

eval "$(luarocks path --bin)"

and it apply the changes, temporarily, to your shell. To have these variables set permanently, you have to configure the environment variables to your shell configuration (for example, by adding the above line to your .bashrc file if your shell is Bash).

Multiple versions using the LuaRocks package loader

If you want to make use of LuaRocks' support for multiple installed versions of modules, you need to load a custom package loader: luarocks.loader.

You should be able to launch the Lua interpreter with the LuaRocks-enabled loader by typing:

lua -lluarocks.loader

Alternatively, you can load the LuaRocks module loader from Lua by issuing this command:

require "luarocks.loader"

If your system is correctly set up so that this command runs with no errors, subsequent calls to require() are LuaRocks-aware and the exact version of each module will be determined based on the dependency tree of previously loaded modules.

Scripts installed by rocks (and the scripts path)

Besides modules, rocks can also install command-line scripts. The default location of this directory (unless you configured your local repository differently) is /usr/local/bin for system-wide installs and ~/.luarocks/bin for per-user installs on Unix and %APPDATA%/luarocks/bin on Windows -- make sure it is in your PATH as well.

If you use the --bin argument in luarocks path, it will also print the appropriate PATH configuration:

luarocks path --bin

Using in Unix systems with sudo

When you use LuaRocks to install a package while you aren't root, the package will get installed in $HOME/.luarocks/ instead of the system-wide (by default, /usr/local/) and become only available for you. Moreover Lua doesn't know with its default setup that packages can be available in the current user's home. If you want to install a package available for all users, you should run it as superuser, typically using sudo.

For example:

sudo luarocks install stdlib

After that, some files may not have correct permissions. For example, if /usr/local/share/lua/5.1/base.lua is only readable by root user, you should at least set them to readable for all users (chmod a+r or chmod 644).

For example:

cd /usr/local/share/lua/5.1
 sudo chmod a+r *

Using a C compiler

Because rocks are generally available in the repository as source rocks rather than binary rocks, it is best to have a C compiler available.

On Windows, MinGW and Microsoft compilers are supported. The compiler should be in the system path, or explicitly configured in the LuaRocks config files. On Windows systems, one way of getting the compiler in the system path is to open the appropriate command prompt as configured by your compiler package (for example, the MSVC Command Prompt for Visual Studio).

Note that for compiling binary rocks that have dependencies on other libraries, LuaRocks needs to be able to find external dependencies.
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