Lua 5.5 Reference Manual

The reference manual is the official definition of the Lua language.
For a complete introduction to Lua programming, see the book Programming in Lua.

Copyright © 2020–2025 Lua.org, PUC-Rio. Freely available under the terms of the Lua license.

Contents

• 1 – Introduction

• 2 – Basic Concepts
  • 2.1 – Values and Types
  • 2.2 – Scopes, Variables, and Environments
  • 2.3 – Error Handling
  • 2.4 – Metatables and Metamethods
  • 2.5 – Garbage Collection
    • 2.5.1 – Incremental Garbage Collection
    • 2.5.2 – Generational Garbage Collection
    • 2.5.3 – Garbage-Collection Metamethods
    • 2.5.4 – Weak Tables
  • 2.6 – Coroutines

• 3 – The Language
  • 3.1 – Lexical Conventions
  • 3.2 – Variables
  • 3.3 – Statements
    • 3.3.1 – Blocks
    • 3.3.2 – Chunks
    • 3.3.3 – Assignment
    • 3.3.4 – Control Structures
    • 3.3.5 – For Statement
    • 3.3.6 – Function Calls as Statements
    • 3.3.7 – Variable Declarations
    • 3.3.8 – To-be-closed Variables
  • 3.4 – Expressions
    • 3.4.1 – Arithmetic Operators
    • 3.4.2 – Bitwise Operators
    • 3.4.3 – Coercions and Conversions
    • 3.4.4 – Relational Operators
    • 3.4.5 – Logical Operators
    • 3.4.6 – Concatenation
    • 3.4.7 – The Length Operator
    • 3.4.8 – Precedence
    • 3.4.9 – Table Constructors
    • 3.4.10 – Function Calls
    • 3.4.11 – Function Definitions
    • 3.4.12 – Lists of expressions, multiple results, and adjustment

  • 4 – The Application Program Interface
    • 4.1 – The Stack
      • 4.1.1 – Stack Size
      • 4.1.2 – Valid and Acceptable Indices
      • 4.1.3 – Pointers to strings
    • 4.2 – C Closures
    • 4.3 – Registry
    • 4.4 – Error Handling in C
      • 4.4.1 – Status Codes
    • 4.5 – Handling Yields in C
    • 4.6 – Functions and Types
    • 4.7 – The Debug Interface

  • 5 – The Auxiliary Library
    • 5.1 – Functions and Types

  • 6 – The Standard Libraries
    • 6.1 – Loading the Libraries in C code
    • 6.2 – Basic Functions
    • 6.3 – Coroutine Manipulation
    • 6.4 – Modules
    • 6.5 – String Manipulation
      • 6.5.1 – Patterns
      • 6.5.2 – Format Strings for Pack and Unpack
    • 6.6 – UTF-8 Support
    • 6.7 – Table Manipulation
    • 6.8 – Mathematical Functions
    • 6.9 – Input and Output Facilities
    • 6.10 – Operating System Facilities
    • 6.11 – The Debug Library

  • 7 – Lua Standalone

  • 8 – Incompatibilities with the Previous Version
    • 8.1 – Incompatibilities in the Language
    • 8.2 – Incompatibilities in the Libraries
    • 8.3 – Incompatibilities in the API

  • 9 – The Complete Syntax of Lua

  Index

  Lua functions basic _G _VERSION assert collectgarbage dofile error getmetatable ipairs load loadfile next pairs pcall print rawequal rawget rawlen rawset require select setmetatable tonumber tostring type warn xpcall coroutine coroutine.close coroutine.create coroutine.isyieldable coroutine.resume coroutine.running coroutine.status coroutine.wrap coroutine.yield debug debug.debug debug.gethook debug.getinfo debug.getlocal debug.getmetatable debug.getregistry debug.getupvalue debug.getuservalue debug.sethook debug.setlocal debug.setmetatable debug.setupvalue debug.setuservalue debug.traceback debug.upvalueid debug.upvaluejoin io io.close io.flush io.input io.lines io.open io.output io.popen io.read io.stderr io.stdin io.stdout io.tmpfile io.type io.write file:close file:flush file:lines file:read file:seek file:setvbuf file:write

  math math.abs math.acos math.asin math.atan math.ceil math.cos math.deg math.exp math.floor math.fmod math.frexp math.huge math.ldexp math.log math.max math.maxinteger math.min math.mininteger math.modf math.pi math.rad math.random math.randomseed math.sin math.sqrt math.tan math.tointeger math.type math.ult os os.clock os.date os.difftime os.execute os.exit os.getenv os.remove os.rename os.setlocale os.time os.tmpname package package.config package.cpath package.loaded package.loadlib package.path package.preload package.searchers package.searchpath string string.byte string.char string.dump string.find string.format string.gmatch string.gsub string.len string.lower string.match string.pack string.packsize string.rep string.reverse string.sub string.unpack string.upper table table.concat table.create table.insert table.move table.pack table.remove table.sort table.unpack utf8 utf8.char utf8.charpattern utf8.codepoint utf8.codes utf8.len utf8.offset metamethods __add __band __bnot __bor __bxor __call __close __concat __div __eq __gc __idiv __index __le __len __lt __metatable __mod __mode __mul __name __newindex __pairs __pow __shl __shr __sub __tostring __unm environment variables LUA_CPATH LUA_CPATH_5_5 LUA_INIT LUA_INIT_5_5 LUA_PATH LUA_PATH_5_5

  C API lua_Alloc lua_CFunction lua_Debug lua_Hook lua_Integer lua_KContext lua_KFunction lua_Number lua_Reader lua_State lua_Unsigned lua_WarnFunction lua_Writer lua_absindex lua_arith lua_atpanic lua_call lua_callk lua_checkstack lua_close lua_closeslot lua_closethread lua_compare lua_concat lua_copy lua_createtable lua_dump lua_error lua_gc lua_getallocf lua_getextraspace lua_getfield lua_getglobal lua_gethook lua_gethookcount lua_gethookmask lua_geti lua_getinfo lua_getiuservalue lua_getlocal lua_getmetatable lua_getstack lua_gettable lua_gettop lua_getupvalue lua_insert lua_isboolean lua_iscfunction lua_isfunction lua_isinteger lua_islightuserdata lua_isnil lua_isnone lua_isnoneornil lua_isnumber lua_isstring lua_istable lua_isthread lua_isuserdata lua_isyieldable lua_len lua_load lua_newstate lua_newtable lua_newthread lua_newuserdatauv lua_next lua_numbertocstring lua_numbertointeger lua_pcall lua_pcallk lua_pop lua_pushboolean lua_pushcclosure lua_pushcfunction lua_pushexternalstring lua_pushfstring lua_pushglobaltable lua_pushinteger lua_pushlightuserdata lua_pushliteral lua_pushlstring lua_pushnil lua_pushnumber lua_pushstring lua_pushthread lua_pushvalue lua_pushvfstring lua_rawequal lua_rawget lua_rawgeti lua_rawgetp lua_rawlen lua_rawset lua_rawseti lua_rawsetp lua_register lua_remove lua_replace lua_resume lua_rotate lua_setallocf lua_setfield lua_setglobal lua_sethook lua_seti lua_setiuservalue lua_setlocal lua_setmetatable lua_settable lua_settop lua_setupvalue lua_setwarnf lua_status lua_stringtonumber lua_toboolean lua_tocfunction lua_toclose lua_tointeger lua_tointegerx lua_tolstring lua_tonumber lua_tonumberx lua_topointer lua_tostring lua_tothread lua_touserdata lua_type lua_typename lua_upvalueid lua_upvalueindex lua_upvaluejoin lua_version lua_warning lua_xmove lua_yield lua_yieldk

  auxiliary library luaL_Buffer luaL_Reg luaL_Stream luaL_addchar luaL_addgsub luaL_addlstring luaL_addsize luaL_addstring luaL_addvalue luaL_alloc luaL_argcheck luaL_argerror luaL_argexpected luaL_buffaddr luaL_buffinit luaL_buffinitsize luaL_bufflen luaL_buffsub luaL_callmeta luaL_checkany luaL_checkinteger luaL_checklstring luaL_checknumber luaL_checkoption luaL_checkstack luaL_checkstring luaL_checktype luaL_checkudata luaL_checkversion luaL_dofile luaL_dostring luaL_error luaL_execresult luaL_fileresult luaL_getmetafield luaL_getmetatable luaL_getsubtable luaL_gsub luaL_len luaL_loadbuffer luaL_loadbufferx luaL_loadfile luaL_loadfilex luaL_loadstring luaL_makeseed luaL_newlib luaL_newlibtable luaL_newmetatable luaL_newstate luaL_openlibs luaL_openselectedlibs luaL_opt luaL_optinteger luaL_optlstring luaL_optnumber luaL_optstring luaL_prepbuffer luaL_prepbuffsize luaL_pushfail luaL_pushresult luaL_pushresultsize luaL_ref luaL_requiref luaL_setfuncs luaL_setmetatable luaL_testudata luaL_tolstring luaL_traceback luaL_typeerror luaL_typename luaL_unref luaL_where standard library luaopen_base luaopen_coroutine luaopen_debug luaopen_io luaopen_math luaopen_os luaopen_package luaopen_string luaopen_table luaopen_utf8 constants LUA_ERRERR LUA_ERRFILE LUA_ERRMEM LUA_ERRRUN LUA_ERRSYNTAX LUA_HOOKCALL LUA_HOOKCOUNT LUA_HOOKLINE LUA_HOOKRET LUA_HOOKTAILCALL LUA_LOADED_TABLE LUA_MASKCALL LUA_MASKCOUNT LUA_MASKLINE LUA_MASKRET LUA_MAXINTEGER LUA_MININTEGER LUA_MINSTACK LUA_MULTRET LUA_NOREF LUA_OK LUA_OPADD LUA_OPBAND LUA_OPBNOT LUA_OPBOR LUA_OPBXOR LUA_OPDIV LUA_OPEQ LUA_OPIDIV LUA_OPLE LUA_OPLT LUA_OPMOD LUA_OPMUL LUA_OPPOW LUA_OPSHL LUA_OPSHR LUA_OPSUB LUA_OPUNM LUA_PRELOAD_TABLE LUA_REFNIL LUA_REGISTRYINDEX LUA_RIDX_GLOBALS LUA_RIDX_MAINTHREAD LUA_TBOOLEAN LUA_TFUNCTION LUA_TLIGHTUSERDATA LUA_TNIL LUA_TNONE LUA_TNUMBER LUA_TSTRING LUA_TTABLE LUA_TTHREAD LUA_TUSERDATA LUA_USE_APICHECK LUA_YIELD LUAL_BUFFERSIZE

  Last update: Sat Nov 15 00:51:05 UTC 2025