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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.

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

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

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coroutine.running()
  • References/Lua/Lua/Standard Libraries/Coroutine Manipulation

coroutine.running () Returns the running coroutine plus a boolean, true when the running coroutine is the main one.

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

tostring (v)string.format If the metatable of v

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

debug.getinfo ([thread,] f [, what]) Returns a table with information about a function. You can give the function directly or you can give a number as the value of f

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

debug.setlocal ([thread,] level, local, value) This function assigns the value value to the local variable with index local of the function at level

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

math.modf (x) Returns the integral part of x and the fractional part of x. Its second result is always a float.

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

string.format (formatstring, ···) Returns a formatted version of its variable number of arguments following the description given in its first argument (which must be a string)

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

setmetatable (table, metatable) Sets the metatable for the given table. (To change the metatable of other types from Lua code, you must use the debug library (

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

math.exp (x) Returns the value ex (where e is the base of natural logarithms).

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