6 – Standard Libraries

The standard Lua libraries provide useful functions that are implemented directly through the C API. Some of these functions provide essential services to the language (e.g., type and getmetatable); others provide access to "outside" services (e.g., I/O); and others could be implemented in Lua itself, but are quite useful or have critical performance requirements that deserve an implementation in C (e.g., table.sort).

All libraries are implemented through the official C API and are provided as separate C modules. Currently, Lua has the following standard libraries:

  • basic library (§6.1);
  • coroutine library (§6.2);
  • package library (§6.3);
  • string manipulation (§6.4);
  • basic UTF-8 support (§6.5);
  • table manipulation (§6.6);
  • mathematical functions (§6.7) (sin, log, etc.);
  • input and output (§6.8);
  • operating system facilities (§6.9);
  • debug facilities (§6.10).

Except for the basic and the package libraries, each library provides all its functions as fields of a global table or as methods of its objects.

To have access to these libraries, the C host program should call the luaL_openlibs function, which opens all standard libraries. Alternatively, the host program can open them individually by using luaL_requiref to call luaopen_base (for the basic library), luaopen_package (for the package library), luaopen_coroutine (for the coroutine library), luaopen_string (for the string library), luaopen_utf8 (for the UTF8 library), luaopen_table (for the table library), luaopen_math (for the mathematical library), luaopen_io (for the I/O library), luaopen_os (for the operating system library), and luaopen_debug (for the debug library). These functions are declared in lualib.h.

math.ceil()
  • References/Lua/Lua/Standard Libraries/Mathematical Functions

math.ceil (x) Returns the smallest integral value larger than or equal to x.

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collectgarbage()
  • References/Lua/Lua/Standard Libraries/Basic Functions

collectgarbage ([opt [, arg]]) This function is a generic interface to the garbage collector. It performs different functions according to its first argument, opt:

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table.unpack()
  • References/Lua/Lua/Standard Libraries/Table Manipulation

table.unpack (list [, i [, j]]) Returns the elements from the given list. This function is equivalent to return list[i], list[i+1]

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math.huge
  • References/Lua/Lua/Standard Libraries/Mathematical Functions

math.huge The float value HUGE_VAL, a value larger than any other numeric value.

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math.acos()
  • References/Lua/Lua/Standard Libraries/Mathematical Functions

math.acos (x) Returns the arc cosine of x (in radians).

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string.find()
  • References/Lua/Lua/Standard Libraries/String Manipulation

string.find (s, pattern [, init [, plain]]) Looks for the first match of pattern (see

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debug.upvalueid()
  • References/Lua/Lua/Standard Libraries/The Debug Library

debug.upvalueid (f, n) Returns a unique identifier (as a light userdata) for the upvalue numbered n from the given function. These unique identifiers allow

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math.tointeger()
  • References/Lua/Lua/Standard Libraries/Mathematical Functions

math.tointeger (x) If the value x is convertible to an integer, returns that integer. Otherwise, returns nil.

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file:read()
  • References/Lua/Lua/Standard Libraries/Input and Output Facilities

file:read (···) Reads the file file, according to the given formats, which specify what to read. For each format, the function returns a string or a number with the

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string.gsub()
  • References/Lua/Lua/Standard Libraries/String Manipulation

string.gsub (s, pattern, repl [, n])snpattern§6.4.1

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