Function Dump/Core Functions

< [[Function Dump]] | [[Core Functions]]

Basic Functions

The basic library provides some core functions to Lua. If you do not include this library in your application, you should check carefully whether you need to provide implementations for some of its facilities.

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!"

Example

assert (false, "This is an error message") 
Will result in:
Tue Oct 07 10:15:37 2008 - Cmd:1: This is an error message
Tue Oct 07 10:15:37 2008 - Cmd, line 1
Tue Oct 07 10:15:37 2008 - stack end

assert (false)
Will result in:
Tue Oct 07 10:14:18 2008 - Cmd:1: assertion failed!
Tue Oct 07 10:14:18 2008 - Cmd, line 1
Tue Oct 07 10:14:18 2008 - stack end

assert (true)

Won't display anything at all.

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/100 as the new value for the pause of the collector (see §2.10).
   * "setstepmul": sets arg/100 as the new value for the step multiplier of the collector (see §2.10).

Example

t = {}
for i = 0,20000 do
	table.insert(t,i,i)
end
print(collectgarbage("count")) --> ~535.7998046875

t = nil

print(collectgarbage("count")) --> ~23.7197265625

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).

Example

File: Hello.txt

Contents: print("Hello World!")

dofile("C:/Hello.txt")

Will result in:
Hello World!

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.

Example

error ("this is an error message")
Will result in:
Tue Oct 07 08:18:36 2008 - Cmd:1: this is an error message
Tue Oct 07 08:18:36 2008 - Cmd, line 1

Tue Oct 07 08:18:36 2008 - stack end

_G

A table that is shared between all scripts in one instance of Roblox. Scripts can use this to share data, including functions, between them.

Notes:

• In Online mode, scripts running in a LocalScript run on the player's computer, so they are in a separate instance of Roblox and can't share data with non-local scripts except by using objects such as IntValue.
• Until recently, this was the table that all the built-in functions were stored in, and it was possible to read values from it without writing "_G" in front. This is no longer the case.

Example

Script one:

_G.variable = "This a variable in _G."

Script two:

while _G.variable == nil do wait() end --make sure that script one sets the variable before this one tries to read it
print(_G.variable)
--Outputs: "This a variable in _G."

See also Global Functions.

gcinfo ()

Returns amount of dynamic memory in use. This is deprecated. Use collectgarbage ("count") instead.

Example

print (gcinfo ())
Will result in something like:
28 

a=collectgarbage ("count") 
print(a)
Will result in something like:
29.6875

getfenv ([f])

Returns the current environment in use by the function. 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.

Example

var1 = 7
var2 = 9
for i, v in pairs(getfenv()) do
	print(i, " = ", v)
end
Output:
script = Script
var1 = 7
var2 = 9

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.

Example

t = {}
print(getmetatable(t))

Will result in:
nil

t = {}
setmetatable(t,{})
print(getmetatable(t))

Will result in:
table: 0687D540

ipairs (t)

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.

Example

days = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}
revdays = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}
for i,v in ipairs(days) do
	revdays[v] = i
	print(revdays[v])
end

Will result in:
1
2
3
4
5
6
7

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 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.

loadfile ([filename])

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

Example

File: file.txt

Contents: print("This is the contents of a file.")

f = loadfile("C:/file.txt")

f()

Will result in:
This is the contents of a file.

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))()

Example

a = 2
loadstring("b = 3")()
print(a+b)

Will result in:
5

newproxy (boolean or proxy)

Undocumented feature of Lua.

Arguments: boolean - returned proxy has metatable or userdata - different proxy created with newproxy

Creates a blank userdata with an empty metatable, or with the metatable of another proxy.

Example

local a = newproxy(true) 
local mt = getmetatable(a) 
print( mt ~= nil ) --> true 

local b = newproxy(a) 
print( mt == getmetatable(b) ) --> true 

local c = newproxy(false) 
print( getmetatable(c) ~= nil ) --> false 

print( a.Name ) --> attempt to index local 'a' (a userdata value) 
mt.__index = {Name="Proxy"} 
print( a.Name ) --> Proxy 
print( b.Name ) --> Proxy

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.

Example

days = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}
print(next(days))
print(next(days,4))

Will result in:
1 Sunday
5 Thursday -- cf. print(days[4]), which gives you Wednesday

pairs (t)

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.

Example

t = {1,2,"a","d",c = 12, q = 20}
for i,v in pairs(t) do
	print(i,v)
end

Will result in:
1 1
2 2
3 a
4 d
c 12
q 20

pcall (f, arg1, ···)

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.

Example

if pcall (function() print("Hi Mom!") end) then
else print("There were errors")
end

Will result in:
Hi Mom!

if pcall (function() ppppprint("Hi Mom!") end) then
else print("There were errors")
end

Will result in:
There were errors

NOTE: You cannot use a function that yields the running coroutine in use by pcall. That includes the wait function. You will get an error about not being able to resume a dead coroutine and not being able to yield across the C boundary.

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.

Example

print ("Hello!")

Will result in:
Hello!

rawequal (v1, v2)

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

Example

print(rawequal (5, 3))

Will result in:
false

print(rawequal (5, 5))

Will result in:
true

rawget (table, index)

Gets the real value of table[index], without invoking any metamethod. table must be a table; index may be any value.

Example

days = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}
print(rawget (days, 2))

Will result in:
Monday

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.

Example

rawset (_G, "test", 42) 
print (test)

Will result in:
42

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.

Example

print(select (3, "a", "b", "c", "d", "e", 1, 2, 3))
Will result in:
c d e 1 2 3
print(select ("#", "a", "b", "c", "d", "e", 1, 2, 3))
Will result in:
8

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.

Example

_G.a = 1   -- create a global variable
setfenv(1, {_G = _G}) -- change current environment
_G.print(a)      --> nil
_G.print(_G.a)   --> 1

Will result in:
nil 1
[http://www.lua.org/pil/14.3.html]

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.

Example

t = {"a","b","c"}
mt = {"Orange","Apple","Microsoft"}

setmetatable(t,mt)

for i,v in pairs(getmetatable(t)) do
	print(i,v)
end

Will result in:
1 Orange
2 Apple
3 Microsoft

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 may have a decimal part, as well as an optional exponent part (see §2.1). In other bases, only unsigned integers are accepted.

Example

print(tonumber (11111111, 2))

Will result in:
255

print(tonumber ("FF", 16))

Will result in:
255

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.

Example

a=tostring("The answer to 2+2 is "  .. 2+2)
print(a)

Will result in:
The answer to 2+2 is 4

type (v)

Returns the type of its only argument, coded as a string. The possible results of this function are "nil" (a string, not the value nil), "number", "string", "boolean", "table", "function", "thread", and "userdata".

Example

print(type (true))

Will result in:
boolean

print(type (3))

Will result in:
number

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 (see §2.5.5).

Example

t = { "the", "quick", "brown" }
print (unpack (t))
Will result in:
the quick brown

_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".

Example

print(_VERSION)

Results in:
Lua 5.1

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.

Example

function handle(err)
	return "ERROR: " .. err:gsub("(.-:)","")
end

function f()
	local a = nil
	return a+1
end

print(xpcall(f,handle))

Will result in:
false ERROR: attempt to perform arithmetic on local 'a' (a nil value)

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