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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.

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

os.execute ([command]) This function is equivalent to the ISO C function system. It passes command to be executed by an operating system shell. Its first

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

math.cos (x) Returns the cosine of x (assumed to be in radians).

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

os.rename (oldname, newname) Renames the file or directory named oldname to newname. If this function fails, it returns nil, plus a string describing

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

os.time ([table]) Returns the current time when called without arguments, or a time representing the local date and time specified by the given table. This table must have fields

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

math.asin (x) Returns the arc sine of x (in radians).

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

package.preload A table to store loaders for specific modules (see require).

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

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

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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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