Module `global`

Lua global variables.

The basic library provides some core functions to Lua. All the preloaded module of Lua are declared here.

Global(s)

_G	A global variable (not a function) that holds the global environment (that is, `_G._G = _G`).
_VERSION	A global variable (not a function) that holds a string containing the current interpreter version.
assert(v, message)	Issues an error when the value of its argument `v` is false (i.e., nil or false); otherwise, returns all its arguments.
collectgarbage(opt, arg)	This function is a generic interface to the garbage collector.
debug	The Debug Library.
dofile(filename)	Opens the named file and executes its contents as a Lua chunk.
error(message, level)	Terminates the last protected function called and returns `message` as the error message.
getfenv(f)	Returns the current environment in use by the function.
getmetatable(object)	If `object` does not have a metatable, returns nil.
ipairs(t)	Use to iterate over a table by index.
load(func, chunkname)	Loads a chunk using function `func` to get its pieces.
loadfile(filename)	Similar to `load`, but gets the chunk from file `filename` or from the standard input, if no file name is given.
loadstring(string, chunkname)	Similar to `load`, but gets the chunk from the given string.
math	This library is an interface to the standard C math library.
next(table, index)	Allows a program to traverse all fields of a table.
os	Operating System Facilities.
pairs(t)	Use to iterate over a table.
pcall(f, ...)	Calls function `f` with the given arguments in protected mode.
print(...)	Receives any number of arguments, and prints their values to `stdout`, using the `tostring` function to convert them to strings.
rawequal(v1, v2)	Checks whether `v1` is equal to `v2`, without invoking any metamethod.
rawget(table, index)	Gets the real value of `table[index]`, without invoking any metamethod.
rawset(table, index, value)	Sets the real value of `table[index]` to `value`, without invoking any metamethod.
require(modname)	Loads the given module.
select(index, ...)	If `index` is a number, returns all arguments after argument number `index`.
setfenv(f, table)	Sets the environment to be used by the given function.
setmetatable(table, metatable)	Sets the metatable for the given table.
string	This library provides generic functions for string manipulation.
table	This library provides generic functions for table manipulation.
tonumber(e, base)	Tries to convert its argument to a number.
tostring(e)	Receives an argument of any type and converts it to a string in a reasonable format.
unpack(list, i, j)	Returns the elements from the given table.
xpcall(f, err)	This function is similar to `pcall`, except that you can set a new error handler.

Global(s)

#table _G

A global variable (not a function) that holds the global environment (that is, _G._G = _G).

Lua itself does not use this variable; changing its value does not affect any environment, nor vice-versa. (Use setfenv to change environments.)

#string _VERSION

A global variable (not a function) that holds a string containing the current interpreter version.

The current contents of this variable is "Lua 5.1".

assert(v, message)

Issues an error when the value of its argument v is false (i.e., nil or false); otherwise, returns all its arguments.

message is an error message; when absent, it defaults to "assertion failed!".

Parameters

v : if this argument is false an error is issued.
#string message : an error message. defaults value is "assertion failed".

Return value

All its arguments.

collectgarbage(opt, arg)

This function is a generic interface to the garbage collector.

It performs different functions according to its first argument, opt:

"stop": stops the garbage collector.
"restart": restarts the garbage collector.
"collect": performs a full garbage-collection cycle.
"count": returns the total memory in use by Lua (in Kbytes).
"step": performs a garbage-collection step. The step "size" is controlled by arg (larger values mean more steps) in a non-specified way. If you want to control the step size you must experimentally tune the value of arg. Returns true if the step finished a collection cycle.
"setpause": sets arg as the new value for the pause of the collector. Returns the previous value for pause.
"setstepmul": sets arg as the new value for the step multiplier of the collector. Returns the previous value for step.

Parameters

#string opt : the command to send.
arg : the argument of the command. (optional)

coroutine#coroutine coroutine

This library provides generic functions for coroutine manipulation.

This is a global variable which hold the preloaded coroutine module.

debug#debug debug

The Debug Library.

This is a global variable which hold the preloaded debug module.

dofile(filename)

Opens the named file and executes its contents as a Lua chunk.

When called without arguments, dofile executes the contents of the standard input (stdin). Returns all values returned by the chunk. In case of errors, dofile propagates the error to its caller (that is, dofile does not run in protected mode).

Parameter

#string filename : the path to the file. (optional)

error(message, level)

Terminates the last protected function called and returns message as the error message.

Function error never returns.

Usually, error adds some information about the error position at the beginning of the message. The level argument specifies how to get the error position.
With level 1 (the default), the error position is where the error function was called.
Level 2 points the error to where the function that called error was called; and so on.
Passing a level 0 avoids the addition of error position information to the message.

Parameters

#string message : an error message.
#number level : specifies how to get the error position, default value is 1.

getfenv(f)

Returns the current environment in use by the function.

Parameter

f : can be a Lua function or a number that specifies the function at that stack level: Level 1 is the function calling getfenv. If the given function is not a Lua function, or if f is 0, getfenv returns the global environment. The default for f is 1.

getmetatable(object)

If object does not have a metatable, returns nil.

Otherwise, if the object's metatable has a "__metatable" field, returns the associated value. Otherwise, returns the metatable of the given object.

Parameter

object :

Return value

#table: the metatable of object.

io#io io

The I/O library provides function for file manipulation.

This is a global variable which hold the preloaded io module.

ipairs(t)

Use to iterate over a table by index.

Returns three values: an iterator function, the table t, and 0, so that the construction :

for i,v in ipairs(t) do *body* end

will iterate over the pairs (1,t[1]), (2,t[2]), ..., up to the first integer key absent from the table.

Parameter

#table t : a table by index.

load(func, chunkname)

Loads a chunk using function func to get its pieces.

Each call to func must return a string that concatenates with previous results. A return of an empty string, nil, or no value signals the end of the chunk.

If there are no errors, returns the compiled chunk as a function; otherwise, returns nil plus the error message. The environment of the returned function is the global environment.

chunkname is used as the chunk name for error messages and debug information. When absent, it defaults to "=(load)".

Parameters

func : function which loads the chunk.
#string chunkname : chunk name used for error messages and debug information, default value is "=(load)".

loadfile(filename)

Similar to load, but gets the chunk from file filename or from the standard input, if no file name is given.

Parameter

#string filename : the path to the file. (optional)

loadstring(string, chunkname)

Similar to load, but gets the chunk from the given string.

To load and run a given string, use the idiom

assert(loadstring(s))()

When absent, chunkname defaults to the given string.

Parameters

#string string : lua code to load.
#string chunkname : chunk name used for error messages and debug information, default value is the given string.

math#math math

This library is an interface to the standard C math library.

This is a global variable which hold the preloaded math module.

next(table, index)

Allows a program to traverse all fields of a table.

Its first argument is a table and its second argument is an index in this table. next returns the next index of the table and its associated value.

When called with nil as its second argument, next returns an initial index and its associated value. When called with the last index, or with nil in an empty table, next returns nil.

If the second argument is absent, then it is interpreted as nil. In particular, you can use next(t) to check whether a table is empty. The order in which the indices are enumerated is not specified, even for numeric indices. (To traverse a table in numeric order, use a numerical for or the ipairs function.)

The behavior of next is undefined if, during the traversal, you assign any value to a non-existent field in the table. You may however modify existing fields. In particular, you may clear existing fields.

Parameters

#table table : table to traverse.
index : initial index.

os#os os

Operating System Facilities.

This is a global variable which hold the preloaded os module.

package#package package

The package library provides basic facilities for loading and building modules in Lua.

This is a global variable which hold the preloaded package module.

pairs(t)

Use to iterate over a table.

Returns three values: the next function, the table t, and nil, so that the construction :

for k,v in pairs(t) do *body* end

will iterate over all key-value pairs of table t.

See function next for the caveats of modifying the table during its traversal.

Parameter

#table t : table to traverse.

pcall(f, ...)

Calls function f with the given arguments in protected mode.

This means that any error inside f is not propagated; instead, pcall catches the error and returns a status code. Its first result is the status code (a boolean), which is true if the call succeeds without errors. In such case, pcall also returns all results from the call, after this first result. In case of any error, pcall returns false plus the error message.

Parameters

f : function to be call in protected mode.
... : function arguments.

Return values

#boolean: true plus the result of f function if its call succeeds without errors.
#boolean, #string: false plus the error message in case of any error.

print(...)

Receives any number of arguments, and prints their values to stdout, using the tostring function to convert them to strings.

print is not intended for formatted output, but only as a quick way to show a value, typically for debugging. For formatted output, use string.format.

Parameter

... : values to print to stdout.

rawequal(v1, v2)

Checks whether v1 is equal to v2, without invoking any metamethod.

Returns a boolean.

Parameters

v1 :
v2 :

Return value

#boolean: true if v1 is equal to v2.

rawget(table, index)

Gets the real value of table[index], without invoking any metamethod.

table must be a table; index may be any value.

Parameters

#table table :
index : may be any value.

Return value

The real value of table[index], without invoking any metamethod.

rawset(table, index, value)

Sets the real value of table[index] to value, without invoking any metamethod.

table must be a table, index any value different from nil, and value any Lua value.
This function returns table.

Parameters

#table table :
index : any value different from nil.
value : any Lua value.

require(modname)

Loads the given module.

The function starts by looking into the package.loaded table to determine whether modname is already loaded. If it is, then require returns the value stored at package.loaded[modname]. Otherwise, it tries to find a loader for the module.

To find a loader, require is guided by the package.loaders array. By changing this array, we can change how require looks for a module. The following explanation is based on the default configuration for package.loaders.

First require queries package.preload[modname]. If it has a value, this value (which should 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 package.cpath. If that also fails, it tries an all-in-one loader (see package.loaders).

Once a loader is found, require calls the loader with a single argument, modname. If the loader returns any value, require assigns the returned value to package.loaded[modname]. If the loader returns no 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].

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

Parameter

#string modname : name of module to load.

select(index, ...)

If index is a number, returns all arguments after argument number index.

Otherwise, index must be the string "#", and select returns the total number of extra arguments it received.

Parameters

index : a number or the string "#"
... :

setfenv(f, table)

Sets the environment to be used by the given function.

f can be a Lua function or a number that specifies the function at that stack level: Level 1 is the function calling setfenv. setfenv returns the given function.
As a special case, when f is 0 setfenv changes the environment of the running thread. In this case, setfenv returns no values.

Parameters

f : a Lua function or a number that specifies the stack level.
#table table : used as environment for f.

Return value

The given function.

setmetatable(table, metatable)

Sets the metatable for the given table.

(You cannot change the metatable of other types from Lua, only from C.) If metatable is nil, removes the metatable of the given table. If the original metatable has a "__metatable" field, raises an error.
This function returns table.

Parameters

#table table :
#table metatable :

Return value

The first argument table.

string#string string

This library provides generic functions for string manipulation.

This is a global variable which hold the preloaded string module.

table#table table

This library provides generic functions for table manipulation.

This is a global variable which hold the preloaded table module.

tonumber(e, base)

Tries to convert its argument to a number.

If the argument is already a number or a string convertible to a number, then tonumber returns this number; otherwise, it returns nil.

An optional argument specifies the base to interpret the numeral. The base may be any integer between 2 and 36, inclusive. In bases above 10, the letter 'A' (in either upper or lower case) represents 10, 'B' represents 11, and so forth, with 'Z' representing 35. In base 10 (the default), the number can have a decimal part, as well as an optional exponent part. In other bases, only unsigned integers are accepted.

Parameters

e : a number or string to convert to a number.
#number base : the base to interpret the numeral, any integer between 2 and 36.(default is 10).

Return value

#number: a number if conversion succeeds else nil.

tostring(e)

Receives an argument of any type and converts it to a string in a reasonable format.

For complete control of how numbers are converted, use string.format.

If the metatable of e has a "__tostring" field, then tostring calls the corresponding value with e as argument, and uses the result of the call as its result.

Parameter

e : an argument of any type.

Return value

#string: a string in a reasonable format.

unpack(list, i, j)

Returns the elements from the given table.

This function is equivalent to

return list[i], list[i+1], ..., list[j]

except that the above code can be written only for a fixed number of elements. By default, i is 1 and j is the length of the list, as defined by the length operator.

Parameters

#table list : a table by index
i : index of first value.
j : index of last value.

xpcall(f, err)

This function is similar to pcall, except that you can set a new error handler.

xpcall calls function f in protected mode, using err as the error handler. Any error inside f is not propagated; instead, xpcall catches the error, calls the err function with the original error object, and returns a status code. Its first result is the status code (a boolean), which is true if the call succeeds without errors. In this case, xpcall also returns all results from the call, after this first result. In case of any error, xpcall returns false plus the result from err.

Parameters

f : function to be call in protected mode.
err : function used as error handler.

Return values

#boolean: true plus the result of f function if its call succeeds without errors.
#boolean, #string: false plus the result of err function.

Modules

Module global

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Module `global`