Welcome to Lua 5.2

About Lua

Lua is a powerful, fast, lightweight, embeddable scripting language developed by a team at PUC-Rio, the Pontifical Catholic University of Rio de Janeiro in Brazil. Lua is free software used in many products and projects around the world.

Lua's official web site provides complete information about Lua, including an executive summary and updated documentation, especially the reference manual, which may differ slightly from the local copy distributed in this package.

Installing Lua

Lua is distributed in source form. You need to build it before using it. Building Lua should be straightforward because Lua is implemented in pure ANSI C and compiles unmodified in all known platforms that have an ANSI C compiler. Lua also compiles unmodified as C++. The instructions given below for building Lua are for Unix-like platforms. See also instructions for other systems and customization options.

If you don't have the time or the inclination to compile Lua yourself, get a binary from LuaBinaries. Try also LuaDist, a multi-platform distribution of Lua that includes batteries.

Building Lua

In most Unix-like platforms, simply do "make" with a suitable target. Here are the details.

1. Open a terminal window and move to the top-level directory, which is named lua-5.2.x. The Makefile there controls both the build process and the installation process.

2. Do "make" and see if your platform is listed. The platforms currently supported are:

   aix ansi bsd freebsd generic linux macosx mingw posix solaris

   If your platform is listed, just do "make xxx", where xxx is your platform name.

   If your platform is not listed, try the closest one or posix, generic, ansi, in this order.

3. The compilation takes only a few moments and produces three files in the src directory: lua (the interpreter), luac (the compiler), and liblua.a (the library).

4. To check that Lua has been built correctly, do "make test" after building Lua. This will run the interpreter and print its version.

If you're running Linux and get compilation errors, make sure you have installed the readline development package (which is probably named libreadline-dev or readline-devel). If you get link errors after that, then try "make linux MYLIBS=-ltermcap".

Installing Lua

Once you have built Lua, you may want to install it in an official place in your system. In this case, do "make install". The official place and the way to install files are defined in the Makefile. You'll probably need the right permissions to install files.

To build and install Lua in one step, do "make xxx install", where xxx is your platform name.

To install Lua locally, do "make local". This will create a directory install with subdirectories bin, include, lib, man, share, and install Lua as listed below. To install Lua locally, but in some other directory, do "make install INSTALL_TOP=xxx", where xxx is your chosen directory. The installation starts in the src and doc directories, so take care if INSTALL_TOP is not an absolute path.

bin:

lua luac

include:

lua.h luaconf.h lualib.h lauxlib.h lua.hpp

lib:

liblua.a

man/man1:

lua.1 luac.1

These are the only directories you need for development. If you only want to run Lua programs, you only need the files in bin and man. The files in include and lib are needed for embedding Lua in C or C++ programs.

Customization

Three kinds of things can be customized by editing a file:

• Where and how to install Lua — edit Makefile.
• How to build Lua — edit src/Makefile.
• Lua features — edit src/luaconf.h.

You don't actually need to edit the Makefiles because you may set the relevant variables in the command line when invoking make. Nevertheless, it's probably best to edit and save the Makefiles to record the changes you've made.

On the other hand, if you need to customize some Lua features, you'll need to edit src/luaconf.h before building and installing Lua. The edited file will be the one installed, and it will be used by any Lua clients that you build, to ensure consistency. Further customization is available to experts by editing the Lua sources.

We strongly recommend that you enable dynamic loading in src/luaconf.h. This is done automatically for all platforms listed above that have this feature and also for Windows.

Building Lua on other systems

If you're not using the usual Unix tools, then the instructions for building Lua depend on the compiler you use. You'll need to create projects (or whatever your compiler uses) for building the library, the interpreter, and the compiler, as follows:

library:

lapi.c lcode.c lctype.c ldebug.c ldo.c ldump.c lfunc.c lgc.c llex.c lmem.c lobject.c lopcodes.c lparser.c lstate.c lstring.c ltable.c ltm.c lundump.c lvm.c lzio.c lauxlib.c lbaselib.c lbitlib.c lcorolib.c ldblib.c liolib.c lmathlib.c loslib.c lstrlib.c ltablib.c loadlib.c linit.c

interpreter:

library, lua.c

compiler:

library, luac.c

To use Lua as a library in your own programs you'll need to know how to create and use libraries with your compiler. Moreover, to dynamically load C libraries for Lua you'll need to know how to create dynamic libraries and you'll need to make sure that the Lua API functions are accessible to those dynamic libraries — but don't link the Lua library into each dynamic library. For Unix, we recommend that the Lua library be linked statically into the host program and its symbols exported for dynamic linking; src/Makefile does this for the Lua interpreter. For Windows, we recommend that the Lua library be a DLL. In all cases, the compiler luac should be linked statically.

As mentioned above, you may edit src/luaconf.h to customize some features before building Lua.

Changes since Lua 5.1

Here are the main changes introduced in Lua 5.2. The reference manual lists the incompatibilities that had to be introduced.

Main changes

• yieldable pcall and metamethods
• new lexical scheme for globals
• ephemeron tables
• new library for bitwise operations
• light C functions
• emergency garbage collector
• goto statement
• finalizers for tables

Language

• no more fenv for threads or functions
• tables honor the __len metamethod
• hex and \z escapes in strings
• support for hexadecimal floats
• order metamethods work for different types
• no more verification of opcode consistency
• hook event "tail return" replaced by "tail call"
• empty statement
• break statement may appear in the middle of a block

Libraries

• arguments for function called through xpcall
• optional 'mode' argument to load and loadfile (to control binary x text)
• optional 'env' argument to load and loadfile (environment for loaded chunk)
• loadlib may load libraries with global names (RTLD_GLOBAL)
• new function package.searchpath
• modules receive their paths when loaded
• optional base in math.log
• optional separator in string.rep
• file:write returns file
• closing a pipe returns exit status
• os.exit may close state
• new metamethods __pairs and __ipairs
• new option 'isrunning' for collectgarbage and lua_gc
• frontier patterns
• \0 in patterns
• new option *L for io.read
• options for io.lines
• debug.getlocal can access function varargs

C API

• main thread predefined in the registry
• new functions lua_absindex, lua_arith, lua_compare, lua_copy, lua_len, lua_rawgetp, lua_rawsetp, lua_upvalueid, lua_upvaluejoin, lua_version.
• new functions luaL_checkversion, luaL_setmetatable, luaL_testudata, luaL_tolstring.
• lua_pushstring and pushlstring return string
• nparams and isvararg available in debug API
• new lua_Unsigned

Implementation

• max constants per function raised to 2²⁶
• generational mode for garbage collection (experimental)
• NaN trick (experimental)
• internal (immutable) version of ctypes
• simpler implementation for string buffers
• parser uses much less C-stack space (no more auto arrays)

Lua standalone interpreter

• new -E option to avoid environment variables
• handling of non-string error messages

License

Lua is free software distributed under the terms of the MIT license reproduced below; it may be used for any purpose, including commercial purposes, at absolutely no cost without having to ask us. The only requirement is that if you do use Lua, then you should give us credit by including the appropriate copyright notice somewhere in your product or its documentation. For details, see this.

Copyright © 1994–2015 Lua.org, PUC-Rio.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.