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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.

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

table.concat (list [, sep [, i [, j]]]) Given a list where all elements are strings or numbers, returns the string list[i]..sep..list[i+1] ··· sep..list[j]. The default

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

type (v)nilnilnumberstringbooleantablefunctionthreaduserdata

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

file:write (···) Writes the value of each of its arguments to file. The arguments must be strings or numbers. In case of success, this function returns file

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

debug.getupvalue (f, up) This function returns the name and the value of the upvalue with index up of the function f. The function returns nil

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package.loadlib()
  • References/Lua/Lua/Standard Libraries/Modules

package.loadlib (libname, funcname) Dynamically links the host program with the C library libname. If funcname is "*", then it

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os.clock()
  • References/Lua/Lua/Standard Libraries/Operating System Facilities

os.clock () Returns an approximation of the amount in seconds of CPU time used by the program.

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

math.abs (x) Returns the absolute value of x. (integer/float)

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

ipairs (t) Returns three values (an iterator function, the table t, and 0) so that the construction for i,v in ipairs(t)

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

string.lower (s)

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

math.randomseed (x) Sets x as the "seed" for the pseudo-random generator: equal seeds produce equal sequences of numbers.

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