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.

io.input()
  • References/Lua/Lua/Standard Libraries/Input and Output Facilities

io.input ([file]) When called with a file name, it opens the named file (in text mode), and sets its handle as the default input file. When called with a file handle, it simply

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

math.sin (x) Returns the sine of x (assumed to be in radians).

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

select (index, ···) If index is a number, returns all arguments after argument number index; a negative number indexes from the end (-1 is the last argument)

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

math.atan (y [, x]) Returns the arc tangent of y/x (in radians), but uses the signs of both parameters to find the quadrant of the result. (It also handles correctly

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

table.insert (list, [pos,] value) Inserts element value at position pos in list, shifting up the elements list[pos], list[pos+1],

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

string.byte (s [, i [, j]])s[i]s[i+1]s[j]iji

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io.close()
  • References/Lua/Lua/Standard Libraries/Input and Output Facilities

io.close ([file]) Equivalent to file:close(). Without a file, closes the default output file.

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

table.remove (list [, pos]) Removes from list the element at position pos, returning the value of the removed element. When pos is an integer

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

pairs (t) If t has a metamethod __pairs, calls it with t as argument and returns the first three results from the call. Otherwise

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package.searchers
  • References/Lua/Lua/Standard Libraries/Modules

package.searchers A table used by require to control how to load modules.

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