Loads the given module. The function starts by looking into the table to determine whether modname is already loaded. If it is, then require returns the value stored at package.loaded[modname]. (The absence of a second result in this case signals that this call did not have to load the module.) Otherwise, it tries to find a loader for the module.

To find a loader, require is guided by the table package.searchers. Each item in this table is a search function, that searches for the module in a particular way. By changing this table, we can change how require looks for a module. The following explanation is based on the default configuration for .

First require queries package.preload[modname]. If it has a value, this value (which must be a function) is the loader. Otherwise require searches for a Lua loader using the path stored in package.path. If that also fails, it searches for a C loader using the path stored in . If that also fails, it tries an all-in-one loader (see package.searchers).

Once a loader is found, require calls the loader with two arguments: modname and an extra value, a loader data, also returned by the searcher. The loader data can be any value useful to the module; for the default searchers, it indicates where the loader was found. (For instance, if the loader came from a file, this extra value is the file path.) If the loader returns any non-nil value, require assigns the returned value to package.loaded[modname]. If the loader does not return a non-nil value and has not assigned any value to package.loaded[modname], then require assigns true to this entry. In any case, require returns the final value of package.loaded[modname]. Besides that value, require also returns as a second result the loader data returned by the searcher, which indicates how require found the module.

If there is any error loading or running the module, or if it cannot find any loader for the module, then require raises an error.

package.config

A string describing some compile-time configurations for packages. This string is a sequence of lines:

• The second line is the character that separates templates in a path. Default is ‘;‘.
• The third line is the string that marks the substitution points in a template. Default is ‘?‘.
• The fourth line is a string that, in a path in Windows, is replaced by the executable’s directory. Default is ‘‘.
• The fifth line is a mark to ignore all text after it when building the luaopen_ function name. Default is ‘-‘.

package.cpath

A string with the path used by to search for a C loader.

Lua initializes the C path package.cpath in the same way it initializes the Lua path , using the environment variable LUA_CPATH_5_4, or the environment variable LUA_CPATH, or a default path defined in luaconf.h.

A table used by require to control which modules are already loaded. When you require a module modname and package.loaded[modname] is not false, simply returns the value stored there.

This variable is only a reference to the real table; assignments to this variable do not change the table used by require.

package.loadlib (libname, funcname)

If funcname is “*“, then it only links with the library, making the symbols exported by the library available to other dynamically linked libraries. Otherwise, it looks for a function funcname inside the library and returns this function as a C function. So, funcname must follow the lua_CFunction prototype (see ).

This is a low-level function. It completely bypasses the package and module system. Unlike require, it does not perform any path searching and does not automatically adds extensions. libname must be the complete file name of the C library, including if necessary a path and an extension. funcname must be the exact name exported by the C library (which may depend on the C compiler and linker used).

This function is not supported by Standard C. As such, it is only available on some platforms (Windows, Linux, Mac OS X, Solaris, BSD, plus other Unix systems that support the dlfcn standard).

package.path

A string with the path used by require to search for a Lua loader.

At start-up, Lua initializes this variable with the value of the environment variable LUA_PATH_5_4 or the environment variable LUA_PATH or with a default path defined in luaconf.h, if those environment variables are not defined. A “;;“ in the value of the environment variable is replaced by the default path.

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

This variable is only a reference to the real table; assignments to this variable do not change the table used by .

package.searchers

A table used by require to control how to find modules.

Each entry in this table is a searcher function. When looking for a module, calls each of these searchers in ascending order, with the module name (the argument given to require) as its sole argument. If the searcher finds the module, it returns another function, the module loader, plus an extra value, a loader data, that will be passed to that loader and returned as a second result by . If it cannot find the module, it returns a string explaining why (or nil if it has nothing to say).

Lua initializes this table with four searcher functions.

The second searcher looks for a loader as a Lua library, using the path stored at package.path. The search is done as described in function .

The third searcher looks for a loader as a C library, using the path given by the variable package.cpath. Again, the search is done as described in function . For instance, if the C path is the string

the searcher for module foo will try to open the files ./foo.so, ./foo.dll, and /usr/local/foo/init.so, in that order. Once it finds a C library, this searcher first uses a dynamic link facility to link the application with the library. Then it tries to find a C function inside the library to be used as the loader. The name of this C function is the string “luaopen_“ concatenated with a copy of the module name where each dot is replaced by an underscore. Moreover, if the module name has a hyphen, its suffix after (and including) the first hyphen is removed. For instance, if the module name is a.b.c-v2.1, the function name will be luaopen_a_b_c.

The fourth searcher tries an all-in-one loader. It searches the C path for a library for the root name of the given module. For instance, when requiring a.b.c, it will search for a C library for a. If found, it looks into it for an open function for the submodule; in our example, that would be luaopen_a_b_c. With this facility, a package can pack several C submodules into one single library, with each submodule keeping its original open function.

All searchers except the first one (preload) return as the extra value the file path where the module was found, as returned by package.searchpath. The first searcher always returns the string “:preload:“.

Searchers should raise no errors and have no side effects in Lua. (They may have side effects in C, for instance by linking the application with a library.)

package.searchpath (name, path [, sep [, rep]])

Searches for the given name in the given path.

A path is a string containing a sequence of templates separated by semicolons. For each template, the function replaces each interrogation mark (if any) in the template with a copy of name wherein all occurrences of sep (a dot, by default) were replaced by rep (the system’s directory separator, by default), and then tries to open the resulting file name.

For instance, if the path is the string

the search for the name foo.a will try to open the files ./foo/a.lua, ./foo/a.lc, and , in that order.