Nvim :help pages, generated
from source
using the tree-sitter-vimdoc parser.
{ a } means 0 or more a's, and [ a ] means an optional a.
lua-names lua-identifiers
Names (also called identifiers) in Lua can be any string of letters, digits,
and underscores, not beginning with a digit. This coincides with the
definition of identifiers in most languages. (The definition of letter depends
on the current locale: any character considered alphabetic by the current
locale can be used in an identifier.) Identifiers are used to name variables
and table fields.
and break do else elseif end false for function if in local nil not or repeat return then true until while
and is a reserved word, but And and AND are
two different, valid names. As a convention, names starting with an underscore
followed by uppercase letters (such as _VERSION) are reserved for internal
global variables used by Lua.
+ - * / % ^ #
== ~= <= >= < > =
( ) { } [ ]
; : , . .. ...
lua-literal
Literal strings can be delimited by matching single or double quotes, and can
contain the following C-like escape sequences:
\a bell
\b backspace
\f form feed
\n newline
\r carriage return
\t horizontal tab
\v vertical tab
\\ backslash
\" quotation mark (double quote)
\' apostrophe (single quote)
\ddd, where ddd is a sequence of up to three
decimal digits. (Note that if a numerical escape is to be followed by a digit,
it must be expressed using exactly three digits.) Strings in Lua may contain
any 8-bit value, including embedded zeros, which can be specified as \0.
[[, an opening long
bracket of level 1 is written as [=[, and so on.
A closing long bracket is defined similarly; for instance, a closing long
bracket of level 4 is written as ]====]. A long string starts with an
opening long bracket of any level and ends at the first closing long bracket
of the same level. Literals in this bracketed form may run for several lines,
do not interpret any escape sequences, and ignore long brackets of any other
level. They may contain anything except a closing bracket of the proper level.
a is coded as 97, newline is coded as 10, and 1 is
coded as 49), the five literals below denote the same string:
a = 'alo\n123"'
a = "alo\n123\""
a = '\97lo\10\04923"'
a = [[alo
123"]]
a = [==[
alo
123"]==]lua-numconstant
A numerical constant may be written with an optional decimal part and an
optional decimal exponent. Lua also accepts integer hexadecimal constants, by
prefixing them with 0x. Examples of valid numerical constants are
3 3.0 3.1416 314.16e-2 0.31416E1 0xff 0x56
lua-comment
A comment starts with a double hyphen (--) anywhere outside a string. If the
text immediately after -- is not an opening long bracket, the comment is a
short comment, which runs until the end of the line. Otherwise, it is a long
comment, which runs until the corresponding closing long bracket. Long
comments are frequently used to disable code temporarily.
lua-types lua-nil
lua-true lua-false
lua-number lua-string
There are eight basic types in Lua: nil, boolean, number, string,
function, userdata, thread, and table. Nil is the type of the value
nil, whose main property is to be different from any other value; it usually
represents the absence of a useful value. Boolean is the type of the values
false and true. Both nil and false make a condition false; any other
value makes it true. Number represents real (double-precision floating-point)
numbers. (It is easy to build Lua interpreters that use other internal
representations for numbers, such as single-precision float or long integers;
see file luaconf.h.) String represents arrays of characters. Lua is 8-bit
clean: strings may contain any 8-bit character, including embedded zeros
(\0) (see lua-literal).
lua-userdatatype
The type userdata is provided to allow arbitrary C data to be stored in Lua
variables. This type corresponds to a block of raw memory and has no
pre-defined operations in Lua, except assignment and identity test. However,
by using metatables, the programmer can define operations for userdata values
(see lua-metatable). Userdata values cannot be created or modified in Lua,
only through the C API. This guarantees the integrity of data owned by the
host program.
lua-thread
The type thread represents independent threads of execution and it is used to
implement coroutines (see lua-coroutine). Do not confuse Lua threads with
operating-system threads. Lua supports coroutines on all systems, even those
that do not support threads.
lua-table
The type table implements associative arrays, that is, arrays that can be
indexed not only with numbers, but with any value (except nil). Tables can
be heterogeneous; that is, they can contain values of all types (except
nil). Tables are the sole data structuring mechanism in Lua; they may be
used to represent ordinary arrays, symbol tables, sets, records, graphs,
trees, etc. To represent records, Lua uses the field name as an index. The
language supports this representation by providing a.name as syntactic sugar
for a["name"]. There are several convenient ways to create tables in Lua
(see lua-tableconstructor).
nil). In
particular, because functions are first-class values, table fields may contain
functions. Thus tables may also carry methods (see lua-function-define).
type returns a string describing the type of a given
value (see lua-type()).
format function from the string library (see
string.format()).
var ::= Name
nil.
var ::= prefixexp [ exp ]
prefixexp) should result in a table value; the second
expression (exp) identifies a specific entry inside that table. The
expression denoting the table to be indexed has a restricted syntax; see
lua-expressions for details.
var.NAME is just syntactic sugar for var["NAME"] :
var ::= prefixexp . Name
getfenv (see
lua_getfenv()). To replace it, you call setfenv (see setfenv()).
(You can only manipulate the environment of C functions through the debug
library; see lua-lib-debug.)
x is equivalent to _env.x, which in turn is
equivalent to
gettable_event(_env, "x")_env is the environment of the running function. (The _env variable is
not defined in Lua. We use it here only for explanatory purposes.)
t[i] is equivalent to a
call gettable_event(t,i). (See lua-metatable for a complete description of
the gettable_event function. This function is not defined or callable in
Lua. We use it here only for explanatory purposes.)
chunk ::= {stat [ ; ]}
;; is not legal.
luac for
details. Programs in source and compiled forms are interchangeable; Lua
automatically detects the file type and acts accordingly.
block ::= chunk
lua-do lua-end
A block may be explicitly delimited to produce a single statement:
stat ::= do block end
return or break statement
in the middle of another block (see lua-control).
stat ::= varlist1 = explist1
varlist1 ::= var { , var }
explist1 ::= exp { , exp }
nils as needed. If the list of expressions ends with a function
call, then all values returned by this call enter in the list of values,
before the adjustment (except when the call is enclosed in parentheses; see
lua-expressions).
i = 3
i, a[i] = i+1, 20a[3] to 20, without affecting a[4] because the i in a[i] is evaluated (to
3) before it is assigned 4. Similarly, the line
x, y = y, xx and y.
t[i] = val is
equivalent to settable_event(t,i,val). (See lua-metatable for a complete
description of the settable_event function. This function is not defined or
callable in Lua. We use it here only for explanatory purposes.)
x = val is equivalent to the
assignment _env.x = val, which in turn is equivalent to
settable_event(_env, "x", val)_env is the environment of the running function. (The _env variable is
not defined in Lua. We use it here only for explanatory purposes.)
lua-if lua-then lua-else lua-elseif
lua-while lua-repeat lua-until
The control structures if, while, and repeat have the usual meaning and
familiar syntax:
stat ::= while exp do block end
stat ::= repeat block until exp
stat ::= if exp then block { elseif exp then block }
[ else block ] end
for statement, in two flavors (see lua-for).
false and nil are considered false. All values different
from nil and false are considered true (in particular, the number 0 and the
empty string are also true).
repeat-until loop, the inner block does not end at the until keyword,
but only after the condition. So, the condition can refer to local variables
declared inside the loop block.
lua-return
The return statement is used to return values from a function or a chunk
(which is just a function). Functions and chunks may return more than one
value, so the syntax for the return statement is
stat ::= return [explist1]
lua-break
The break statement is used to terminate the execution of a while, repeat,
or for loop, skipping to the next statement after the loop:
stat ::= break
break ends the innermost enclosing loop.
return and break statements can only be written as the last
statement of a block. If it is really necessary to return or break in the
middle of a block, then an explicit inner block can be used, as in the idioms
do return end and do break end, because now return and break are
the last statements in their (inner) blocks.
for statement has two forms: one numeric and one generic.
for loop repeats a block of code while a control variable runs
through an arithmetic progression. It has the following syntax:
stat ::= for Name = exp , exp [ , exp ] do block end
block is repeated for name starting at the value of the first exp, until
it passes the second exp by steps of the third exp. More precisely,
a for statement like
for var = e1, e2, e3 do block end
do
local var, limit, step = tonumber(e1), tonumber(e2), tonumber(e3)
if not ( var and limit and step ) then error() end
while ( step >0 and var <= limit )
or ( step <=0 and var >= limit ) do
block
var = var + step
end
endvar, limit and step are invisible variables. The names are here for
explanatory purposes only.
break to exit a for loop.
var is local to the loop; you cannot use its value
after the for ends or is broken. If you need this value, assign it to
another variable before breaking or exiting the loop.
for-in
The generic for statement works over functions, called iterators. On each
iteration, the iterator function is called to produce a new value, stopping
when this new value is nil. The generic for loop has the following syntax:
stat ::= for namelist in explist1 do block end
namelist ::= Name { , Name }
for statement like
for var1, ..., varn in explist do block end
do
local f, s, var = explist
while true do
local var1, ..., varn = f(s, var)
var = var1
if var == nil then break end
block
end
endexplist is evaluated only once. Its results are an iterator function,
a state, and an initial value for the first iterator variable.
f, s, and var are invisible variables. The names are here for
explanatory purposes only.
break to exit a for loop.
var1, ..., varn are local to the loop; you cannot use
their values after the for ends. If you need these values, then assign
them to other variables before breaking or exiting the loop.
stat ::= functioncall
stat ::= local namelist [ = explist1 ]
namelist ::= Name { , Name }
nil.
exp ::= prefixexp exp ::= nil | false | true exp ::= Number exp ::= String exp ::= function exp ::= tableconstructor exp ::= ... exp ::= exp binop exp exp ::= unop exp prefixexp ::= var | functioncall | ( exp )
...), can only be used inside vararg functions;
they are explained in lua-function-define.
not (see lua-logicalop), and the unary length operator (see lua-length).
f() -- adjusted to 0 results
g(f(), x) -- f() is adjusted to 1 result
g(x, f()) -- g gets x plus all results from f()
a,b,c = f(), x -- f() is adjusted to 1 result (c gets nil)
a,b = ... -- a gets the first vararg parameter, b gets
-- the second (both a and b may get nil if there
-- is no corresponding vararg parameter)
a,b,c = x, f() -- f() is adjusted to 2 results
a,b,c = f() -- f() is adjusted to 3 results
return f() -- returns all results from f()
return ... -- returns all received vararg parameters
return x,y,f() -- returns x, y, and all results from f()
{f()} -- creates a list with all results from f()
{...} -- creates a list with all vararg parameters
{f(), nil} -- f() is adjusted to 1 result(f(x,y,z)) is always a single value, even if f returns several values.
(The value of (f(x,y,z)) is the first value returned by f or nil if f does not
return any values.)
+ (addition),
- (subtraction), * (multiplication), / (division), % (modulo)
and ^ (exponentiation); and unary - (negation). If the operands are numbers,
or strings that can be converted to numbers (see lua-coercion), then all
operations have the usual meaning. Exponentiation works for any exponent. For
instance, x^(-0.5) computes the inverse of the square root of x. Modulo is
defined as
a % b == a - math.floor(a/b)*b== ~= < > <= >=
false or true.
==) first compares the type of its operands. If the types are
different, then the result is false. Otherwise, the values of the operands
are compared. Numbers and strings are compared in the usual way. Objects
(tables, userdata, threads, and functions) are compared by reference: two
objects are considered equal only if they are the same object. Every time you
create a new object (a table, userdata, or function), this new object is
different from any previously existing object.
"0"==0 evaluates to false, and t[0] and
t["0"] denote different entries in a table.
~= is exactly the negation of equality (==).
and or not
false and nil as false and anything else as true.
lua-not lua-and lua-or
The negation operator not always returns false or true. The conjunction
operator and returns its first argument if this value is false or nil;
otherwise, and returns its second argument. The disjunction
operator or returns its first argument if this value is different
from nil and false; otherwise, or returns its second argument.
Both and and or use short-cut evaluation, that is, the second operand is
evaluated only if necessary. Here are some examples:
10 or 20 --> 10 10 or error() --> 10 nil or "a" --> "a" nil and 10 --> nil false and error() --> false false and nil --> false false or nil --> nil 10 and 20 --> 20
--> indicates the result of the preceding expression.)
..).
If both operands are strings or numbers, then they are converted to strings
according to the rules mentioned in lua-coercion. Otherwise, the
"concat" metamethod is called (see lua-metatable).
#. The length of a
string is its number of bytes (that is, the usual meaning of string length
when each character is one byte).
t is defined to be any integer index n such that t[n] is
not nil and t[n+1] is nil; moreover, if t[1] is nil, n may be zero. For a
regular array, with non-nil values from 1 to a given n, its length is exactly
that n, the index of its last value. If the array has "holes" (that
is, nil values between other non-nil values), then #t may be any of the
indices that directly precedes a nil value (that is, it may consider any
such nil value as the end of the array).
or and < > <= >= ~= == .. + - * / not # - (unary) ^
..) and exponentiation (^) operators are right
associative. All other binary operators are left associative.
tableconstructor ::= { [ fieldlist ] }
fieldlist ::= field { fieldsep field } [ fieldsep ]
field ::= [ exp ] = exp | Name = exp | exp
fieldsep ::= , | ;
[exp1] = exp2 adds to the new table an entry with
key exp1 and value exp2. A field of the form name = exp is equivalent to
["name"] = exp. Finally, fields of the form exp are equivalent to
[i] = exp, where i are consecutive numerical integers, starting with 1.
Fields in the other formats do not affect this counting. For example,
a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 }do
local t = {}
t[f(1)] = g
t[1] = "x" -- 1st exp
t[2] = "y" -- 2nd exp
t.x = 1 -- temp["x"] = 1
t[3] = f(x) -- 3rd exp
t[30] = 23
t[4] = 45 -- 4th exp
a = t
endexp and the expression is a
function call, then all values returned by the call enter the list
consecutively (see lua-function). To avoid this, enclose the function
call in parentheses (see lua-expressions).
functioncall ::= prefixexp args
prefixexp and args are evaluated. If the value
of prefixexp has type function, then this function is called with the given
arguments. Otherwise, the prefixexp "call" metamethod is called, having as
first parameter the value of prefixexp, followed by the original call
arguments (see lua-metatable).
functioncall ::= prefixexp : Name args
v:name( args ) is syntactic sugar
for v.name(v, args ), except that v is evaluated only once.
args ::= ( [ explist1 ] ) args ::= tableconstructor args ::= String
f{ fields } is syntactic sugar for f({ fields }), that is, the
argument list is a single new table. A call of the form f' string '
(or f" string " or f[[ string ]]) is syntactic sugar for
f(' string '), that is, the argument list is a single literal string.
( in a function call. This restriction avoids some ambiguities
in the language. If you write
a = f
(g).x(a)a = f(g).x(a). So, if you want two
statements, you must add a semi-colon between them. If you actually want to
call f, you must remove the line break before (g).
lua-tailcall
A call of the form return functioncall is called a tail call. Lua
implements proper tail calls (or proper tail recursion): in a tail call, the
called function reuses the stack entry of the calling function. Therefore,
there is no limit on the number of nested tail calls that a program can
execute. However, a tail call erases any debug information about the calling
function. Note that a tail call only happens with a particular syntax, where
the return has one single function call as argument; this syntax makes the
calling function return exactly the returns of the called function. So, none
of the following examples are tail calls:
return (f(x)) -- results adjusted to 1
return 2 * f(x)
return x, f(x) -- additional results
f(x); return -- results discarded
return x or f(x) -- results adjusted to 1function ::= function funcbody funcbody ::= ( [ parlist1 ] ) block end
stat ::= function funcname funcbody
stat ::= local function Name funcbody
funcname ::= Name { . Name } [ : Name ]
function f () body end
f = function () body end
function t.a.b.c.f () body end
t.a.b.c.f = function () body end
local function f () body end
local f; f = function f () body end
local f = function f () body end
f.)
lua-closure
A function definition is an executable expression, whose value has type
function. When Lua pre-compiles a chunk, all its function bodies are
pre-compiled too. Then, whenever Lua executes the function definition, the
function is instantiated (or closed). This function instance (or closure) is
the final value of the expression. Different instances of the same function
may refer to different external local variables and may have different
environment tables.
parlist1 ::= namelist [ , ... ] | ...
lua-vararg
When a function is called, the list of arguments is adjusted to the length of
the list of parameters, unless the function is a variadic or vararg function,
which is indicated by three dots (...) at the end of its parameter list. A
vararg function does not adjust its argument list; instead, it collects all
extra arguments and supplies them to the function through a vararg expression,
which is also written as three dots. The value of this expression is a list of
all actual extra arguments, similar to a function with multiple results. If a
vararg expression is used inside another expression or in the middle of a list
of expressions, then its return list is adjusted to one element. If the
expression is used as the last element of a list of expressions, then no
adjustment is made (unless the call is enclosed in parentheses).
function f(a, b) end
function g(a, b, ...) end
function r() return 1,2,3 endCALL PARAMETERS f(3) a=3, b=nil f(3, 4) a=3, b=4 f(3, 4, 5) a=3, b=4 f(r(), 10) a=1, b=10 f(r()) a=1, b=2 g(3) a=3, b=nil, ... --> (nothing) g(3, 4) a=3, b=4, ... --> (nothing) g(3, 4, 5, 8) a=3, b=4, ... --> 5 8 g(5, r()) a=5, b=1, ... --> 2 3
return statement (see lua-control).
If control reaches the end of a function without encountering
a return statement, then the function returns with no results.
lua-colonsyntax
The colon syntax is used for defining methods, that is, functions that have an
implicit extra parameter self. Thus, the statement
function t.a.b.c:f ( params ) body end
t.a.b.c:f = function ( self, params ) body end
x = 10 -- global variable
do -- new block
local x = x -- new `x`, with value 10
print(x) --> 10
x = x+1
do -- another block
local x = x+1 -- another `x`
print(x) --> 12
end
print(x) --> 11
end
print(x) --> 10 (the global one)local x = x, the new x being declared is
not in scope yet, and so the second x refers to the outside variable.
lua-upvalue
Because of the lexical scoping rules, local variables can be freely accessed
by functions defined inside their scope. A local variable used by an inner
function is called an upvalue, or external local variable, inside the inner
function.
a = {}
local x = 20
for i=1,10 do
local y = 0
a[i] = function () y=y+1; return x+y end
endy variable, while all of
them share the same x.
error function (see
error()). If you need to catch errors in Lua, you can use the pcall
function (see pcall()).
"__add" in its metatable. If it finds one, Lua calls that function
to perform the addition.
getmetatable function
(see getmetatable()).
setmetatable function (see
setmetatable()). You cannot change the metatable of other types from Lua
(except using the debug library); you must use the C API for that.
__; for instance, the key for operation "add"
is the string "__add". The semantics of these operations is better explained
by a Lua function describing how the interpreter executes that operation.
rawget, tonumber, etc.) are
described in lua-lib-core. In particular, to retrieve the metamethod of a
given object, we use the expression
metatable(obj)[event]
rawget(metatable(obj) or {}, event)nil).
__add()
------
the + operation.
getbinhandler below defines how Lua chooses a handler for a
binary operation. First, Lua tries the first operand. If its type does not
define a handler for the operation, then Lua tries the second operand.
function getbinhandler (op1, op2, event)
return metatable(op1)[event] or metatable(op2)[event]
endop1 + op2 is
function add_event (op1, op2)
local o1, o2 = tonumber(op1), tonumber(op2)
if o1 and o2 then -- both operands are numeric?
return o1 + o2 -- `+` here is the primitive `add`
else -- at least one of the operands is not numeric
local h = getbinhandler(op1, op2, "__add")
if h then
-- call the handler with both operands
return h(op1, op2)
else -- no handler available: default behavior
error(...)
end
end
end__sub()
------
the - operation. Behavior similar to the "add" operation.
__mul()
------
the * operation. Behavior similar to the "add" operation.
__div()
------
the / operation. Behavior similar to the "add" operation.
__mod()
------
the % operation. Behavior similar to the "add" operation, with the
operation o1 - floor(o1/o2)*o2 as the primitive operation.
__pow()
------
the ^ (exponentiation) operation. Behavior similar to the "add" operation,
with the function pow (from the C math library) as the primitive operation.
__unm()
------
the unary - operation.
function unm_event (op)
local o = tonumber(op)
if o then -- operand is numeric?
return -o -- `-` here is the primitive `unm`
else -- the operand is not numeric.
-- Try to get a handler from the operand
local h = metatable(op).__unm
if h then
-- call the handler with the operand
return h(op)
else -- no handler available: default behavior
error(...)
end
end
end__concat()
---------
the .. (concatenation) operation.
function concat_event (op1, op2)
if (type(op1) == "string" or type(op1) == "number") and
(type(op2) == "string" or type(op2) == "number") then
return op1 .. op2 -- primitive string concatenation
else
local h = getbinhandler(op1, op2, "__concat")
if h then
return h(op1, op2)
else
error(...)
end
end
end__len()
------
the # operation.
function len_event (op)
if type(op) == "string" then
return strlen(op) -- primitive string length
elseif type(op) == "table" then
return #op -- primitive table length
else
local h = metatable(op).__len
if h then
-- call the handler with the operand
return h(op)
else -- no handler available: default behavior
error(...)
end
end
end__eq()
-----
the == operation.
getcomphandler defines how Lua chooses a metamethod for
comparison operators. A metamethod only is selected when both objects being
compared have the same type and the same metamethod for the selected
operation.
function getcomphandler (op1, op2, event)
if type(op1) ~= type(op2) then return nil end
local mm1 = metatable(op1)[event]
local mm2 = metatable(op2)[event]
if mm1 == mm2 then return mm1 else return nil end
endfunction eq_event (op1, op2)
if type(op1) ~= type(op2) then -- different types?
return false -- different objects
end
if op1 == op2 then -- primitive equal?
return true -- objects are equal
end
-- try metamethod
local h = getcomphandler(op1, op2, "__eq")
if h then
return h(op1, op2)
else
return false
end
enda ~= b is equivalent to not (a == b).
__lt()
-----
the < operation.
function lt_event (op1, op2)
if type(op1) == "number" and type(op2) == "number" then
return op1 < op2 -- numeric comparison
elseif type(op1) == "string" and type(op2) == "string" then
return op1 < op2 -- lexicographic comparison
else
local h = getcomphandler(op1, op2, "__lt")
if h then
return h(op1, op2)
else
error(...);
end
end
enda > b is equivalent to b < a.
__le()
-----
the <= operation.
function le_event (op1, op2)
if type(op1) == "number" and type(op2) == "number" then
return op1 <= op2 -- numeric comparison
elseif type(op1) == "string" and type(op2) == "string" then
return op1 <= op2 -- lexicographic comparison
else
local h = getcomphandler(op1, op2, "__le")
if h then
return h(op1, op2)
else
h = getcomphandler(op1, op2, "__lt")
if h then
return not h(op2, op1)
else
error(...);
end
end
end
enda >= b is equivalent to b <= a. Note that, in the absence of a "le"
metamethod, Lua tries the "lt", assuming that a <= b is equivalent
to not (b < a).
__index()
--------
The indexing access table[key].
function gettable_event (table, key)
local h
if type(table) == "table" then
local v = rawget(table, key)
if v ~= nil then return v end
h = metatable(table).__index
if h == nil then return nil end
else
h = metatable(table).__index
if h == nil then
error(...);
end
end
if type(h) == "function" then
return h(table, key) -- call the handler
else return h[key] -- or repeat operation on it
end__newindex()
-----------
The indexing assignment table[key] = value.
function settable_event (table, key, value)
local h
if type(table) == "table" then
local v = rawget(table, key)
if v ~= nil then rawset(table, key, value); return end
h = metatable(table).__newindex
if h == nil then rawset(table, key, value); return end
else
h = metatable(table).__newindex
if h == nil then
error(...);
end
end
if type(h) == "function" then
return h(table, key,value) -- call the handler
else h[key] = value -- or repeat operation on it
end__call()
-------
called when Lua calls a value.
function function_event (func, ...)
if type(func) == "function" then
return func(...) -- primitive call
else
local h = metatable(func).__call
if h then
return h(func, ...)
else
error(...)
end
end
endsetfenv. You can get the environment of a Lua function or the
running thread by calling getfenv (see lua_getfenv()). To manipulate the
environment of other objects (userdata, C functions, other threads) you must
use the C API.
lua_gc (see lua_gc()) in C or
collectgarbage (see collectgarbage()) in Lua. Both get percentage points
as arguments (so an argument of 100 means a real value of 1). With these
functions you can also control the collector directly (e.g., stop and restart
it).
__gc
Garbage userdata with a field __gc in their metatables are not collected
immediately by the garbage collector. Instead, Lua puts them in a list. After
the collection, Lua does the equivalent of the following function for each
userdata in that list:
function gc_event (udata)
local h = metatable(udata).__gc
if h then
h(udata)
end
end__mode
A weak table can have weak keys, weak values, or both. A table with weak keys
allows the collection of its keys, but prevents the collection of its values.
A table with both weak keys and weak values allows the collection of both keys
and values. In any case, if either the key or the value is collected, the
whole pair is removed from the table. The weakness of a table is controlled by
the value of the __mode field of its metatable. If the __mode field is a
string containing the character k, the keys in the table are weak.
If __mode contains v, the values in the table are weak.
__mode. Otherwise, the weak behavior of the tables controlled by this
metatable is undefined.
coroutine.create (see
coroutine.create()). Its sole argument is a function that is the main
function of the coroutine. The create function only creates a new coroutine
and returns a handle to it (an object of type thread); it does not start the
coroutine execution.
coroutine.resume (see coroutine.resume()),
passing as its first argument the thread returned by coroutine.create, the
coroutine starts its execution, at the first line of its main function. Extra
arguments passed to coroutine.resume are passed on to the coroutine main
function. After the coroutine starts running, it runs until it terminates or
yields.
coroutine.resume returns true, plus any values returned by the coroutine
main function. In case of errors, coroutine.resume returns false plus an
error message.
coroutine.yield (see
coroutine.yield()). When a coroutine yields, the corresponding
coroutine.resume returns immediately, even if the yield happens inside
nested function calls (that is, not in the main function, but in a function
directly or indirectly called by the main function). In the case of a yield,
coroutine.resume also returns true, plus any values passed to
coroutine.yield. The next time you resume the same coroutine, it continues
its execution from the point where it yielded, with the call to
coroutine.yield returning any extra arguments passed to coroutine.resume.
coroutine.create, the coroutine.wrap function (see
coroutine.wrap()) also creates a coroutine, but instead of returning
the coroutine itself, it returns a function that, when called, resumes the
coroutine. Any arguments passed to this function go as extra arguments to
coroutine.resume. coroutine.wrap returns all the values returned by
coroutine.resume, except the first one (the boolean error code). Unlike
coroutine.resume, coroutine.wrap does not catch errors; any error is
propagated to the caller.
function foo1 (a)
print("foo", a)
return coroutine.yield(2*a)
end
co = coroutine.create(function (a,b)
print("co-body", a, b)
local r = foo1(a+1)
print("co-body", r)
local r, s = coroutine.yield(a+b, a-b)
print("co-body", r, s)
return b, "end"
end)
print("main", coroutine.resume(co, 1, 10))
print("main", coroutine.resume(co, "r"))
print("main", coroutine.resume(co, "x", "y"))
print("main", coroutine.resume(co, "x", "y"))co-body 1 10 foo 2 main true 4 co-body r main true 11 -9 co-body x y main true 10 end main false cannot resume dead coroutine
lua.h.
macro instead. All such macros use each of its arguments exactly once
(except for the first argument, which is always a Lua state), and so do not
generate hidden side-effects.
luai_apicheck,in file
luaconf.h.
nil, number, string, etc.).
lua-stackindex
For convenience, most query operations in the API do not follow a strict stack
discipline. Instead, they can refer to any element in the stack by using an
index: a positive index represents an absolute stack position (starting at 1);
a negative index represents an offset from the top of the stack. More
specifically, if the stack has n elements, then index 1 represents the first
element (that is, the element that was pushed onto the stack first) and index
n represents the last element; index -1 also represents the last element
(that is, the element at the top) and index -n represents the first element.
We say that an index is valid if it lies between 1 and the stack top (that is,
if 1 <= abs(index) <= top).
lua_checkstack to grow the stack size (see
lua_checkstack()).
LUA_MINSTACK stack positions
are available. LUA_MINSTACK is defined as 20, so that usually you do not
have to worry about stack space unless your code has loops pushing elements
onto the stack.
lua_checkstack. Such indices are called acceptable indices. More formally,
we define an acceptable index as follows:
(index < 0 && abs(index) <= top) || (index > 0 && index <= stackspace)LUA_GLOBALSINDEX. The environment of the running C function is always at
pseudo-index LUA_ENVIRONINDEX.
lua_getfield(L, LUA_GLOBALSINDEX, varname);lua_upvalueindex. The first value associated with a function is at position
lua_upvalueindex(1), and so on. Any access to lua_upvalueindex( n ),
where n is greater than the number of upvalues of the current function,
produces an acceptable (but invalid) index.
LUA_REGISTRYINDEX. Any C library can store data into this
table, but it should take care to choose keys different from those used by
other libraries, to avoid collisions. Typically, you should use as key a
string containing your library name or a light userdata with the address of a
C object in your code.
longjmp facility to handle errors. (You can also
choose to use exceptions if you use C++; see file luaconf.h.) When Lua faces
any error (such as memory allocation errors, type errors, syntax errors, and
runtime errors) it raises an error; that is, it does a long jump. A protected
environment uses setjmp to set a recover point; any error jumps to the most
recent active recover point.
lua_newstate, lua_close, lua_load, lua_pcall, and lua_cpcall (see
lua_newstate(), lua_close(), lua_load(),
lua_pcall(), and lua_cpcall()).
lua_error (see
lua_error()).
lua_Alloc
typedef void * (*lua_Alloc) (void *ud,
void *ptr,
size_t osize,
size_t nsize);realloc,
but not exactly the same. Its arguments are ud, an opaque pointer
passed to lua_newstate (see lua_newstate()); ptr, a pointer
to the block being allocated/reallocated/freed; osize, the original
size of the block; nsize, the new size of the block. ptr is NULL
if and only if osize is zero. When nsize is zero, the allocator
must return NULL; if osize is not zero, it should free the block
pointed to by ptr. When nsize is not zero, the allocator returns
NULL if and only if it cannot fill the request. When nsize is not
zero and osize is zero, the allocator should behave like malloc.
When nsize and osize are not zero, the allocator behaves like
realloc. Lua assumes that the allocator never fails whenosize >=
nsize`.
luaL_newstate (see
luaL_newstate()).
static void *l_alloc (void *ud, void *ptr, size_t osize,
size_t nsize) {
(void)ud; (void)osize; /* not used */
if (nsize == 0) {
free(ptr);
return NULL;
}
else
return realloc(ptr, nsize);
}free(NULL) has no effect and that
realloc(NULL, size) is equivalent to malloc(size). ANSI C ensures both
behaviors.
lua_atpanic()
lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);panic function and then calls exit(EXIT_FAILURE), thus exiting
the host application. Your panic function may avoid this exit by never
returning (e.g., doing a long jump).
lua_call()
void lua_call (lua_State *L, int nargs, int nresults);lua_call; nargs is the number of
arguments that you pushed onto the stack. All arguments and the
function value are popped from the stack when the function is called.
The function results are pushed onto the stack when the function
returns. The number of results is adjusted to nresults, unless
nresults is LUA_MULTRET. In this case, all results from the
function are pushed. Lua takes care that the returned values fit into
the stack space. The function results are pushed onto the stack in
direct order (the first result is pushed first), so that after the
call the last result is on the top of the stack.
longjmp).
a = f("how", t.x, 14)lua_getfield(L, LUA_GLOBALSINDEX, "f"); // function to be called
lua_pushstring(L, "how"); // 1st argument
lua_getfield(L, LUA_GLOBALSINDEX, "t"); // table to be indexed
lua_getfield(L, -1, "x"); // push result of t.x (2nd arg)
lua_remove(L, -2); // remove 't' from the stack
lua_pushinteger(L, 14); // 3rd argument
lua_call(L, 3, 1); // call 'f' with 3 arguments and 1 result
lua_setfield(L, LUA_GLOBALSINDEX, "a"); // set global 'a'lua_gettop(L) (see lua_gettop()) returns the
number of arguments received by the function. The first argument (if
any) is at index 1 and its last argument is at index lua_gettop(L).
To return values to Lua, a C function just pushes them onto the stack,
in direct order (the first result is pushed first), and returns the
number of results. Any other value in the stack below the results will
be properly discarded by Lua. Like a Lua function, a C function called
by Lua can also return many results.
lua-cfunctionexample
As an example, the following function receives a variable number of
numerical arguments and returns their average and sum:
static int foo (lua_State *L) {
int n = lua_gettop(L); /* number of arguments */
lua_Number sum = 0;
int i;
for (i = 1; i <= n; i++) {
if (!lua_isnumber(L, i)) {
lua_pushstring(L, "incorrect argument");
lua_error(L);
}
sum += lua_tonumber(L, i);
}
lua_pushnumber(L, sum/n); /* first result */
lua_pushnumber(L, sum); /* second result */
return 2; /* number of results */
}lua_checkstack()
int lua_checkstack (lua_State *L, int extra);extra free stack slots in the stack.
It returns false if it cannot grow the stack to that size. This
function never shrinks the stack; if the stack is already larger than
the new size, it is left unchanged.
lua_close()
void lua_close (lua_State *L);lua_concat()
void lua_concat (lua_State *L, int n);n values at the top of the stack, pops them, and
leaves the result at the top. If n is 1, the result is the single
string on the stack (that is, the function does nothing); if n is 0,
the result is the empty string. Concatenation is done following the
usual semantics of Lua (see lua-concat).
lua_cpcall()
int lua_cpcall (lua_State *L, lua_CFunction func, void *ud);func in protected mode. func starts with only
one element in its stack, a light userdata containing ud. In case of
errors, lua_cpcall returns the same error codes as lua_pcall (see
lua_pcall()), plus the error object on the top of the stack;
otherwise, it returns zero, and does not change the stack. All values
returned by func are discarded.
lua_createtable()
void lua_createtable (lua_State *L, int narr, int nrec);narr array elements and nrec non-array
elements. This pre-allocation is useful when you know exactly how many
elements the table will have. Otherwise you can use the function
lua_newtable (see lua_newtable()).
lua_dump()
int lua_dump (lua_State *L, lua_Writer writer, void *data);lua_dump calls function writer (see
lua_Writer) with the given data to write them.
lua_equal()
int lua_equal (lua_State *L, int index1, int index2);index1 and
index2 are equal, following the semantics of the Lua == operator
(that is, may call metamethods). Otherwise returns 0. Also returns 0
if any of the indices is non valid.
lua_error()
int lua_error (lua_State *L);lua_gc()
int lua_gc (lua_State *L, int what, int data);what:
LUA_GCSTOP stops the garbage collector.
LUA_GCRESTART restarts the garbage collector.
LUA_GCCOLLECT performs a full garbage-collection cycle.
LUA_GCCOUNT returns the current amount of memory (in Kbytes) in
use by Lua.
LUA_GCCOUNTB returns the remainder of dividing the current
amount of bytes of memory in use by Lua by 1024.
LUA_GCSTEP performs an incremental step of garbage collection.
The step "size" is controlled by data (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 data. The
function returns 1 if the step finished a
garbage-collection cycle.
LUA_GCSETPAUSE sets data /100 as the new value for the
pause of the collector (see lua-gc).
The function returns the previous value of the
pause.
LUA_GCSETSTEPMULsets data /100 as the new value for the
step multiplier of the collector (see
lua-gc). The function returns the
previous value of the step multiplier.
lua_getallocf()
lua_Alloc lua_getallocf (lua_State *L, void **ud);ud is
not NULL, Lua stores in *ud the opaque pointer passed to
lua_newstate (see lua_newstate()).
lua_getfenv()
void lua_getfenv (lua_State *L, int index);lua_getfield()
void lua_getfield (lua_State *L, int index, const char *k);t[k], where t is the value at the
given valid index index. As in Lua, this function may trigger a
metamethod for the "index" event (see lua-metatable).
lua_getglobal()
void lua_getglobal (lua_State *L, const char *name);name. It is defined as
a macro:
#define lua_getglobal(L,s) lua_getfield(L, LUA_GLOBALSINDEX, s)lua_getmetatable()
int lua_getmetatable (lua_State *L, int index);lua_gettable()
void lua_gettable (lua_State *L, int index);t[k], where t is the value at the
given valid index index and k is the value at the top of the
stack.
lua_gettop()
int lua_gettop (lua_State *L);lua_insert()
void lua_insert (lua_State *L, int index);lua_Integer
typedef ptrdiff_t lua_Integer;ptrdiff_t, which is usually the largest integral
type the machine handles "comfortably".
lua_isboolean()
int lua_isboolean (lua_State *L, int index);lua_iscfunction()
int lua_iscfunction (lua_State *L, int index);lua_isfunction()
int lua_isfunction (lua_State *L, int index);lua_islightuserdata()
int lua_islightuserdata (lua_State *L, int index);lua_isnil()
int lua_isnil (lua_State *L, int index);nil, and 0
otherwise.
lua_isnumber()
int lua_isnumber (lua_State *L, int index);lua_isstring()
int lua_isstring (lua_State *L, int index);lua_istable()
int lua_istable (lua_State *L, int index);lua_isthread()
int lua_isthread (lua_State *L, int index);lua_isuserdata()
int lua_isuserdata (lua_State *L, int index);lua_lessthan()
int lua_lessthan (lua_State *L, int index1, int index2);index1 is smaller than
the value at acceptable index index2, following the semantics of the
Lua < operator (that is, may call metamethods). Otherwise returns 0.
Also returns 0 if any of the indices is non valid.
lua_load()
int lua_load (lua_State *L,
lua_Reader reader,
void *data,
const char *chunkname);lua_load pushes the
compiled chunk as a Lua function on top of the stack. Otherwise, it
pushes an error message. The return values of lua_load are:
0: no errors;
LUA_ERRSYNTAX : syntax error during pre-compilation;
LUA_ERRMEM : memory allocation error.
lua_load automatically detects whether the chunk is text or binary,
and loads it accordingly (see program luac).
lua_load function uses a user-supplied reader function to read
the chunk (see lua_Reader). The data argument is an opaque
value passed to the reader function.
chunkname argument gives a name to the chunk, which is used for
error messages and in debug information (see lua-apiDebug).
lua_newstate()
lua_State *lua_newstate (lua_Alloc f, void *ud);NULL if cannot create the
state (due to lack of memory). The argument f is the allocator
function; Lua does all memory allocation for this state through this
function. The second argument, ud, is an opaque pointer that Lua
simply passes to the allocator in every call.
lua_newtable()
void lua_newtable (lua_State *L);lua_createtable(L, 0, 0) (see
lua_createtable()).
lua_newthread()
lua_State *lua_newthread (lua_State *L);lua_State (see lua_State) that represents this new
thread. The new state returned by this function shares with the
original state all global objects (such as tables), but has an
independent execution stack.
lua_newuserdata()
void *lua_newuserdata (lua_State *L, size_t size);userdata
Userdata represents C values in Lua. A full userdata represents a
block of memory. It is an object (like a table): you must create it,
it can have its own metatable, and you can detect when it is being
collected. A full userdata is only equal to itself (under raw
equality).
gc metamethod, Lua calls
the metamethod and marks the userdata as finalized. When this userdata
is collected again then Lua frees its corresponding memory.
lua_next()
int lua_next (lua_State *L, int index);lua_next returns 0 (and pushes
nothing).
lua-tabletraversal
A typical traversal looks like this:
/* table is in the stack at index 't' */
lua_pushnil(L); /* first key */
while (lua_next(L, t) != 0) {
/* uses 'key' (at index -2) and 'value' (at index -1) */
printf("%s - %s\n",
lua_typename(L, lua_type(L, -2)),
lua_typename(L, lua_type(L, -1)));
/* removes 'value'; keeps 'key' for next iteration */
lua_pop(L, 1);
}lua_tolstring (see
lua_tolstring()) directly on a key, unless you know that the
key is actually a string. Recall that lua_tolstring changes the
value at the given index; this confuses the next call to lua_next.
lua_Number
typedef double lua_Number;luaconf.h.
lua_objlen()
size_t lua_objlen (lua_State *L, int index);#); for userdata, this is the size of the
block of memory allocated for the userdata; for other values, it is 0.
lua_pcall()
lua_pcall (lua_State *L, int nargs, int nresults, int errfunc);nargs and nresults have the same meaning as in lua_call
(see lua_call()). If there are no errors during the call,
lua_pcall behaves exactly like lua_call. However, if there is any
error, lua_pcall catches it, pushes a single value on the stack (the
error message), and returns an error code. Like lua_call,
lua_pcall always removes the function and its arguments from the
stack.
errfunc is 0, then the error message returned on the stack is
exactly the original error message. Otherwise, errfunc is the stack
index of an error handler function. (In the current
implementation, this index cannot be a pseudo-index.) In case of
runtime errors, this function will be called with the error message
and its return value will be the message returned on the stack by
lua_pcall.
lua_pcall, since
by then the stack has unwound.
lua_pcall function returns 0 in case of success or one of the
following error codes (defined in lua.h):
LUA_ERRRUN a runtime error.
LUA_ERRMEM memory allocation error. For such errors, Lua does
not call the error handler function.
LUA_ERRERR error while running the error handler function.
lua_pop()
void lua_pop (lua_State *L, int n);n elements from the stack.
lua_pushboolean()
void lua_pushboolean (lua_State *L, int b);b onto the stack.
lua_pushcclosure()
void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);lua_pushcclosure is called to create and push
the C function onto the stack, with the argument n telling how many
values should be associated with the function. lua_pushcclosure also
pops these values from the stack.
lua_pushcfunction()
void lua_pushcfunction (lua_State *L, lua_CFunction f);function that, when called, invokes the corresponding C function.
lua_pushcfunction is defined as a macro:
#define lua_pushcfunction(L,f) lua_pushcclosure(L,f,0)lua_pushfstring()
const char *lua_pushfstring (lua_State *L, const char *fmt, ...);sprintf, but has some
important differences:
%%
(inserts a % in the string), %s (inserts a zero-terminated
string, with no size restrictions), %f (inserts a
lua_Number), %p (inserts a pointer as a hexadecimal numeral),
%d (inserts an int), and %c (inserts an int as a
character).
lua_pushinteger()
void lua_pushinteger (lua_State *L, lua_Integer n);n onto the stack.
lua_pushlightuserdata()
void lua_pushlightuserdata (lua_State *L, void *p);lua-lightuserdata
Userdata represents C values in Lua. A light userdata represents a
pointer. It is a value (like a number): you do not create it, it has
no individual metatable, and it is not collected (as it was never
created). A light userdata is equal to "any" light userdata with the
same C address.
lua_pushlstring()
void lua_pushlstring (lua_State *L, const char *s, size_t len);s with size len onto the stack.
Lua makes (or reuses) an internal copy of the given string, so the
memory at s can be freed or reused immediately after the function
returns. The string can contain embedded zeros.
lua_pushnil()
void lua_pushnil (lua_State *L);lua_pushnumber()
void lua_pushnumber (lua_State *L, lua_Number n);n onto the stack.
lua_pushstring()
void lua_pushstring (lua_State *L, const char *s);s onto the stack.
Lua makes (or reuses) an internal copy of the given string, so the
memory at s can be freed or reused immediately after the function
returns. The string cannot contain embedded zeros; it is assumed to
end at the first zero.
lua_pushthread()
int lua_pushthread (lua_State *L);L onto the stack. Returns 1 if this
thread is the main thread of its state.
lua_pushvalue()
void lua_pushvalue (lua_State *L, int index);lua_pushvfstring()
const char *lua_pushvfstring (lua_State *L,
const char *fmt,
va_list argp);lua_pushfstring (see lua_pushfstring()), except
that it receives a va_list instead of a variable number of
arguments.
lua_rawequal()
int lua_rawequal (lua_State *L, int index1, int index2);index1 and
index2 are primitively equal (that is, without calling metamethods).
Otherwise returns 0. Also returns 0 if any of the indices are non
valid.
lua_rawget()
void lua_rawget (lua_State *L, int index);lua_gettable (see lua_gettable()), but does a raw
access (i.e., without metamethods).
lua_rawgeti()
void lua_rawgeti (lua_State *L, int index, int n);t[n], where t is the value at the
given valid index index. The access is raw; that is, it does not
invoke metamethods.
lua_rawset()
void lua_rawset (lua_State *L, int index);lua_settable (see lua_settable()), but does a raw
assignment (i.e., without metamethods).
lua_rawseti()
void lua_rawseti (lua_State *L, int index, int n);t[n] = v, where t is the value at the given
valid index index and v is the value at the top of the stack.
lua_Reader
typedef const char * (*lua_Reader) (lua_State *L,
void *data,
size_t *size);lua_load (see lua_load()). Every
time it needs another piece of the chunk, lua_load calls the reader,
passing along its data parameter. The reader must return a pointer
to a block of memory with a new piece of the chunk and set size to
the block size. The block must exist until the reader function is
called again. To signal the end of the chunk, the reader must return
NULL. The reader function may return pieces of any size greater than
zero.
lua_register()
void lua_register (lua_State *L,
const char *name,
lua_CFunction f);f as the new value of global name. It is
defined as a macro:
#define lua_register(L,n,f) \
(lua_pushcfunction(L, f), lua_setglobal(L, n))lua_remove()
void lua_remove (lua_State *L, int index);lua_replace()
void lua_replace (lua_State *L, int index);lua_resume()
int lua_resume (lua_State *L, int narg);lua_resume (see
lua_resume()) with narg being the number of arguments. This
call returns when the coroutine suspends or finishes its execution.
When it returns, the stack contains all values passed to lua_yield
(see lua_yield()), or all values returned by the body function.
lua_resume returns LUA_YIELD if the coroutine yields, 0 if the
coroutine finishes its execution without errors, or an error code in
case of errors (see lua_pcall()). In case of errors, the stack
is not unwound, so you can use the debug API over it. The error
message is on the top of the stack. To restart a coroutine, you put on
its stack only the values to be passed as results from lua_yield,
and then call lua_resume.
lua_setallocf()
void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);f with user data
ud.
lua_setfenv()
int lua_setfenv (lua_State *L, int index);lua_setfenv returns 0.
Otherwise it returns 1.
lua_setfield()
void lua_setfield (lua_State *L, int index, const char *k);t[k] = v, where t is the value at the given
valid index index and v is the value at the top of the stack.
lua_setglobal()
void lua_setglobal (lua_State *L, const char *name);name. It is defined as a macro:
#define lua_setglobal(L,s) lua_setfield(L, LUA_GLOBALSINDEX, s)lua_setmetatable()
int lua_setmetatable (lua_State *L, int index);lua_settable()
void lua_settable (lua_State *L, int index);t[k] = v, where t is the value at the given
valid index index, v is the value at the top of the stack, and k
is the value just below the top.
lua_settop()
void lua_settop (lua_State *L, int index);nil. If index is 0, then all stack
elements are removed.
lua_State
typedef struct lua_State lua_State;lua_newstate (see
lua_newstate()), which creates a Lua state from scratch.
lua_status()
int lua_status (lua_State *L);L.
LUA_YIELD if the thread is
suspended.
lua_toboolean()
int lua_toboolean (lua_State *L, int index);lua_toboolean returns 1 for
any Lua value different from false and nil; otherwise it returns
0. It also returns 0 when called with a non-valid index. (If you want
to accept only actual boolean values, use lua_isboolean
lua_isboolean() to test the value's type.)
lua_tocfunction()
lua_CFunction lua_tocfunction (lua_State *L, int index);NULL.
lua_tointeger()
lua_Integer lua_tointeger (lua_State *L, int idx);lua_Integer (see lua_Integer). The Lua value
must be a number or a string convertible to a number (see
lua-coercion); otherwise, lua_tointeger returns 0.
lua_tolstring()
const char *lua_tolstring (lua_State *L, int index, size_t *len);len is not NULL, it also sets *len with the string length. The
Lua value must be a string or a number; otherwise, the function
returns NULL. If the value is a number, then lua_tolstring also
changes the actual value in the stack to a string. (This change
confuses lua_next lua_next() when lua_tolstring is applied
to keys during a table traversal.)
lua_tolstring returns a fully aligned pointer to a string inside the
Lua state. This string always has a zero (\0) after its last
character (as in C), but may contain other zeros in its body. Because
Lua has garbage collection, there is no guarantee that the pointer
returned by lua_tolstring will be valid after the corresponding
value is removed from the stack.
lua_tonumber()
lua_Number lua_tonumber (lua_State *L, int index);lua_Number (see lua_Number). The Lua value must be a number
or a string convertible to a number (see lua-coercion);
otherwise, lua_tonumber returns 0.
lua_topointer()
const void *lua_topointer (lua_State *L, int index);void*). The value may be a userdata, a table, a thread, or
a function; otherwise, lua_topointer returns NULL. Different
objects will give different pointers. There is no way to convert the
pointer back to its original value.
lua_tostring()
const char *lua_tostring (lua_State *L, int index);lua_tothread()
lua_State *lua_tothread (lua_State *L, int index);lua_State* lua_State). This value must be a
thread; otherwise, the function returns NULL.
lua_touserdata()
void *lua_touserdata (lua_State *L, int index);NULL.
lua_type()
int lua_type (lua_State *L, int index);LUA_TNONE for a non-valid index (that is, an index to an "empty"
stack position). The types returned by lua_type are coded by the
following constants defined in lua.h : LUA_TNIL, LUA_TNUMBER,
LUA_TBOOLEAN, LUA_TSTRING, LUA_TTABLE, LUA_TFUNCTION,
LUA_TUSERDATA, LUA_TTHREAD, and LUA_TLIGHTUSERDATA.
lua_typename()
const char *lua_typename (lua_State *L, int tp);tp, which must be
one the values returned by lua_type.
lua_Writer
typedef int (*lua_Writer) (lua_State *L,
const void* p,
size_t sz,
void* ud);lua_dump (see lua_dump()). Every
time it produces another piece of chunk, lua_dump calls the writer,
passing along the buffer to be written (p), its size (sz), and the
data parameter supplied to lua_dump.
lua_dump from calling the writer again.
lua_xmove()
void lua_xmove (lua_State *from, lua_State *to, int n);same global state.
n values from the stack from, and pushes them
onto the stack to.
lua_yield()
int lua_yield (lua_State *L, int nresults);return lua_yield (L, nresults);lua_yield in that way, the running coroutine
suspends its execution, and the call to lua_resume (see
lua_resume()) that started this coroutine returns. The
parameter nresults is the number of values from the stack that are
passed as results to lua_resume.
lua-stackexample
As an example of stack manipulation, if the stack starts as
10 20 30 40 50* (from bottom to top; the * marks the top), then
lua_pushvalue(L, 3) --> 10 20 30 40 50 30* lua_pushvalue(L, -1) --> 10 20 30 40 50 30 30* lua_remove(L, -3) --> 10 20 30 40 30 30* lua_remove(L, 6) --> 10 20 30 40 30* lua_insert(L, 1) --> 30 10 20 30 40* lua_insert(L, -1) --> 30 10 20 30 40* (no effect) lua_replace(L, 2) --> 30 40 20 30* lua_settop(L, -3) --> 30 40* lua_settop(L, 6) --> 30 40 nil nil nil nil*
lua_Debug
typedef struct lua_Debug {
int event;
const char *name; /* (n) */
const char *namewhat; /* (n) */
const char *what; /* (S) */
const char *source; /* (S) */
int currentline; /* (l) */
int nups; /* (u) number of upvalues */
int linedefined; /* (S) */
int lastlinedefined; /* (S) */
char short_src[LUA_IDSIZE]; /* (S) */
/* private part */
other fields
} lua_Debug;lua_getstack (see lua_getstack()) fills only the private part
of this structure, for later use. To fill the other fields of lua_Debug with
useful information, call lua_getinfo (see lua_getinfo()).
lua_Debug have the following meaning:
source If the function was defined in a string, then source is
that string. If the function was defined in a file, then
source starts with a @ followed by the file name.
short_src a "printable" version of source, to be used in error messages.
linedefined the line number where the definition of the function starts.
lastlinedefined the line number where the definition of the function ends.
what the string "Lua" if the function is a Lua function,
"C" if it is a C function, "main" if it is the main
part of a chunk, and "tail" if it was a function that
did a tail call. In the latter case, Lua has no other
information about the function.
currentline the current line where the given function is executing.
When no line information is available, currentline is
set to -1.
name a reasonable name for the given function. Because
functions in Lua are first-class values, they do not have
a fixed name: some functions may be the value of multiple
global variables, while others may be stored only in a
table field. The lua_getinfo function checks how the
function was called to find a suitable name. If it cannot
find a name, then name is set to NULL.
namewhat explains the name field. The value of namewhat can be
"global", "local", "method", "field",
"upvalue", or "" (the empty string), according to how
the function was called. (Lua uses the empty string when
no other option seems to apply.) nups the number of
upvalues of the function.
lua_gethook()
lua_Hook lua_gethook (lua_State *L);lua_gethookcount()
int lua_gethookcount (lua_State *L);lua_gethookmask()
int lua_gethookmask (lua_State *L);lua_getinfo()
int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);ar
must be a valid activation record that was filled by a previous call
to lua_getstack (see lua_getstack()) or given as argument to
a hook (see lua_Hook).
what string with the character >. (In that case,
lua_getinfo pops the function in the top of the stack.) For
instance, to know in which line a function f was defined, you can
write the following code:
lua_Debug ar;
lua_getfield(L, LUA_GLOBALSINDEX, "f"); /* get global 'f' */
lua_getinfo(L, ">S", &ar);
printf("%d\n", ar.linedefined);what selects some fields of the
structure ar to be filled or a value to be pushed on the stack:
'n' fills in the field name and namewhat
'S' fills in the fields source, short_src, linedefined,
lastlinedefined, and what
'l' fills in the field currentline
'u' fills in the field nups
'f' pushes onto the stack the function that is running at the
given level
'L' pushes onto the stack a table whose indices are the numbers
of the lines that are valid on the function. (A valid line is a
line with some associated code, that is, a line where you can put
a break point. Non-valid lines include empty lines and comments.)
what).
lua_getlocal()
const char *lua_getlocal (lua_State *L, lua_Debug *ar, int n);ar must be a valid activation record that was filled
by a previous call to lua_getstack (see lua_getstack()) or
given as argument to a hook (see lua_Hook). The index n
selects which local variable to inspect (1 is the first parameter or
active local variable, and so on, until the last active local
variable). lua_getlocal pushes the variable's value onto the stack
and returns its name.
( (open parentheses) represent
internal variables (loop control variables, temporaries, and C
function locals).
NULL (and pushes nothing) when the index is greater than the
number of active local variables.
lua_getstack()
int lua_getstack (lua_State *L, int level, lua_Debug *ar);lua_Debug (see lua_Debug)
structure with an identification of the activation record of the
function executing at a given level. Level 0 is the current running
function, whereas level n+1 is the function that has called level
n. When there are no errors, lua_getstack returns 1; when called
with a level greater than the stack depth, it returns 0.
lua_getupvalue()
const char *lua_getupvalue (lua_State *L, int funcindex, int n);lua_getupvalue gets
the index n of an upvalue, pushes the upvalue's value onto the
stack, and returns its name. funcindex points to the closure in the
stack. (Upvalues have no particular order, as they are active through
the whole function. So, they are numbered in an arbitrary order.)
NULL (and pushes nothing) when the index is greater than the
number of upvalues. For C functions, this function uses the empty
string "" as a name for all upvalues.
lua_Hook
typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);ar argument has its field event set
to the specific event that triggered the hook. Lua identifies these
events with the following constants: LUA_HOOKCALL, LUA_HOOKRET,
LUA_HOOKTAILRET, LUA_HOOKLINE, and LUA_HOOKCOUNT. Moreover, for
line events, the field currentline is also set. To get the value of
any other field in ar, the hook must call lua_getinfo (see
lua_getinfo()). For return events, event may be
LUA_HOOKRET, the normal value, or LUA_HOOKTAILRET. In the latter
case, Lua is simulating a return from a function that did a tail call;
in this case, it is useless to call lua_getinfo.
lua_sethook()
int lua_sethook (lua_State *L, lua_Hook f, int mask, int count);f is the hook function. mask specifies on which events
the hook will be called: it is formed by a bitwise or of the
constants LUA_MASKCALL, LUA_MASKRET, LUA_MASKLINE, and
LUA_MASKCOUNT. The count argument is only meaningful when the mask
includes LUA_MASKCOUNT. For each event, the hook is called as
explained below:
The call hook: is called when the interpreter calls a function.
The hook is called just after Lua enters the new function, before
the function gets its arguments.
The return hook: is called when the interpreter returns from a
function. The hook is called just before Lua leaves the function.
You have no access to the values to be returned by the function.
The line hook: is called when the interpreter is about to start
the execution of a new line of code, or when it jumps back in the
code (even to the same line). (This event only happens while Lua is
executing a Lua function.)
The count hook: is called after the interpreter executes every
count instructions. (This event only happens while Lua is
executing a Lua function.)
mask to zero.
lua_setlocal()
const char *lua_setlocal (lua_State *L, lua_Debug *ar, int n);ar and n are as in lua_getlocal (see
lua_getlocal()). lua_setlocal assigns the value at the top of
the stack to the variable and returns its name. It also pops the value
from the stack.
NULL (and pops nothing) when the index is greater than the
number of active local variables.
lua_setupvalue()
const char *lua_setupvalue (lua_State *L, int funcindex, int n);funcindex and n are as in the
lua_getupvalue (see lua_getupvalue()).
NULL (and pops nothing) when the index is greater than the
number of upvalues.
lua-debugexample
As an example, the following function lists the names of all local
variables and upvalues for a function at a given level of the stack:
int listvars (lua_State *L, int level) {
lua_Debug ar;
int i;
const char *name;
if (lua_getstack(L, level, &ar) == 0)
return 0; /* failure: no such level in the stack */
i = 1;
while ((name = lua_getlocal(L, &ar, i++)) != NULL) {
printf("local %d %s\n", i-1, name);
lua_pop(L, 1); /* remove variable value */
}
lua_getinfo(L, "f", &ar); /* retrieves function */
i = 1;
while ((name = lua_getupvalue(L, -1, i++)) != NULL) {
printf("upvalue %d %s\n", i-1, name);
lua_pop(L, 1); /* remove upvalue value */
}
return 1;
}lauxlib.h
and have a prefix luaL_.
luaL_check* or luaL_opt*. All of these
functions raise an error if the check is not satisfied. Because the error
message is formatted for arguments (e.g., "bad argument #1"), you should not
use these functions for other stack values.
luaL_addchar()
void luaL_addchar (luaL_Buffer *B, char c);luaL_addlstring()
void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);s with length l to the buffer B
(see luaL_Buffer). The string may contain embedded zeros.
luaL_addsize()
void luaL_addsize (luaL_Buffer *B, size_t n);B (see luaL_Buffer) a string of length
n previously copied to the buffer area (see
luaL_prepbuffer()).
luaL_addstring()
void luaL_addstring (luaL_Buffer *B, const char *s);s to the buffer B
(see luaL_Buffer). The string may not contain embedded zeros.
luaL_addvalue()
void luaL_addvalue (luaL_Buffer *B);B (see
luaL_Buffer). Pops the value.
luaL_argcheck()
void luaL_argcheck (lua_State *L,
int cond,
int narg,
const char *extramsg);cond is true. If not, raises an error with the
following message, where func is retrieved from the call stack:
bad argument #<narg> to <func> (<extramsg>)
luaL_argerror()
int luaL_argerror (lua_State *L, int narg, const char *extramsg);func is retrieved
from the call stack:
bad argument #<narg> to <func> (<extramsg>)
return luaL_argerror( args ).
luaL_Buffer
typedef struct luaL_Buffer luaL_Buffer;string buffer.
b of type luaL_Buffer.
luaL_buffinit(L, &b) (see
luaL_buffinit()).
luaL_add* functions.
luaL_pushresult(&b) (see
luaL_pushresult()). This call leaves the final string on the
top of the stack.
luaL_addvalue
luaL_addvalue().) After calling luaL_pushresult the stack is
back to its level when the buffer was initialized, plus the final
string on its top.
luaL_buffinit()
void luaL_buffinit (lua_State *L, luaL_Buffer *B);B. This function does not allocate any space;
the buffer must be declared as a variable (see luaL_Buffer).
luaL_callmeta()
int luaL_callmeta (lua_State *L, int obj, const char *e);obj has a metatable and this metatable has a
field e, this function calls this field and passes the object as its
only argument. In this case this function returns 1 and pushes onto
the stack the value returned by the call. If there is no metatable or
no metamethod, this function returns
0 (without pushing any value on the stack).
luaL_checkany()
void luaL_checkany (lua_State *L, int narg);nil) at position narg.
luaL_checkint()
int luaL_checkint (lua_State *L, int narg);narg is a number and returns
this number cast to an int.
luaL_checkinteger()
lua_Integer luaL_checkinteger (lua_State *L, int narg);narg is a number and returns
this number cast to a lua_Integer (see lua_Integer).
luaL_checklong()
long luaL_checklong (lua_State *L, int narg);narg is a number and returns
this number cast to a long.
luaL_checklstring()
const char *luaL_checklstring (lua_State *L, int narg, size_t *l);narg is a string and returns
this string; if l is not NULL fills *l with the string's length.
luaL_checknumber()
lua_Number luaL_checknumber (lua_State *L, int narg);narg is a number and returns
this number (see lua_Number).
luaL_checkoption()
int luaL_checkoption (lua_State *L,
int narg,
const char *def,
const char *const lst[]);narg is a string and searches
for this string in the array lst (which must be NULL-terminated).
Returns the index in the array where the string was found. Raises an
error if the argument is not a string or if the string cannot be
found.
def is not NULL, the function uses def as a default value
when there is no argument narg or if this argument is nil.
luaL_checkstack()
void luaL_checkstack (lua_State *L, int sz, const char *msg);top + sz elements, raising an error if the
stack cannot grow to that size. msg is an additional text to go into
the error message.
luaL_checkstring()
const char *luaL_checkstring (lua_State *L, int narg);narg is a string and returns
this string.
luaL_checktype()
void luaL_checktype (lua_State *L, int narg, int t);luaL_checkudata()
void *luaL_checkudata (lua_State *L, int narg, const char *tname);narg is a userdata of the type
tname (see luaL_newmetatable()).
luaL_dofile()
int luaL_dofile (lua_State *L, const char *filename);(luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0))luaL_dostring()
int luaL_dostring (lua_State *L, const char *str);(luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0))luaL_error()
int luaL_error (lua_State *L, const char *fmt, ...);fmt plus any
extra arguments, following the same rules of lua_pushfstring (see
lua_pushfstring()). It also adds at the beginning of the
message the file name and the line number where the error occurred, if
this information is available.
return luaL_error( args ).
luaL_getmetafield()
int luaL_getmetafield (lua_State *L, int obj, const char *e);e from the metatable of the object
at index obj. If the object does not have a metatable, or if the
metatable does not have this field, returns 0 and pushes nothing.
luaL_getmetatable()
void luaL_getmetatable (lua_State *L, const char *tname);tname in
the registry (see luaL_newmetatable()).
luaL_gsub()
const char *luaL_gsub (lua_State *L,
const char *s,
const char *p,
const char *r);s by replacing any occurrence of the string
p with the string r. Pushes the resulting string on the stack and
returns it.
luaL_loadbuffer()
int luaL_loadbuffer (lua_State *L,
const char *buff,
size_t sz,
const char *name);lua_load (see
lua_load()) to load the chunk in the buffer pointed to by
buff with size sz.
lua_load. name is the
chunk name, used for debug information and error messages.
luaL_loadfile()
int luaL_loadfile (lua_State *L, const char *filename);lua_load (see
lua_load()) to load the chunk in the file named filename. If
filename is NULL, then it loads from the standard input. The first
line in the file is ignored if it starts with a #.
lua_load, but it has an
extra error code LUA_ERRFILE if it cannot open/read the file.
lua_load, this function only loads the chunk; it does not run it.
luaL_loadstring()
int luaL_loadstring (lua_State *L, const char *s);lua_load (see
lua_load()) to load the chunk in the zero-terminated string
s.
lua_load.
lua_load, this function only loads the chunk; it does not
run it.
luaL_newmetatable()
int luaL_newmetatable (lua_State *L, const char *tname);tname, returns 0. Otherwise,
creates a new table to be used as a metatable for userdata, adds it to
the registry with key tname, and returns 1.
tname in the registry.
luaL_newstate()
lua_State *luaL_newstate (void);lua_newstate (see
lua_newstate()) with an allocator based on the standard C
realloc function and then sets a panic function (see
lua_atpanic()) that prints an error message to the standard
error output in case of fatal errors.
NULL if there is a memory allocation
error.
luaL_openlibs()
void luaL_openlibs (lua_State *L);luaL_optint()
int luaL_optint (lua_State *L, int narg, int d);narg is a number, returns this number cast
to an int. If this argument is absent or is nil, returns d.
Otherwise, raises an error.
luaL_optinteger()
lua_Integer luaL_optinteger (lua_State *L,
int narg,
lua_Integer d);narg is a number, returns this number cast
to a lua_Integer (see lua_Integer). If this argument is
absent or is nil, returns d. Otherwise, raises an error.
luaL_optlong()
long luaL_optlong (lua_State *L, int narg, long d);narg is a number, returns this number cast
to a long. If this argument is absent or is nil, returns d.
Otherwise, raises an error.
luaL_optlstring()
const char *luaL_optlstring (lua_State *L,
int narg,
const char *d,
size_t *l);narg is a string, returns this string. If
this argument is absent or is nil, returns d. Otherwise, raises an
error.
l is not NULL, fills the position *l with the results' length.
luaL_optnumber()
lua_Number luaL_optnumber (lua_State *L, int narg, lua_Number d);narg is a number, returns this number. If
this argument is absent or is nil, returns d. Otherwise, raises an
error.
luaL_optstring()
const char *luaL_optstring (lua_State *L,
int narg,
const char *d);narg is a string, returns this string. If
this argument is absent or is nil, returns d. Otherwise, raises an
error.
luaL_prepbuffer()
char *luaL_prepbuffer (luaL_Buffer *B);LUAL_BUFFERSIZE where you can
copy a string to be added to buffer B (see luaL_Buffer).
After copying the string into this space you must call luaL_addsize
(see luaL_addsize()) with the size of the string to actually
add it to the buffer.
luaL_pushresult()
void luaL_pushresult (luaL_Buffer *B);B leaving the final string on the top of
the stack.
luaL_ref()
int luaL_ref (lua_State *L, int t);reference, in the table at index t, for the
object at the top of the stack (and pops the object).
t, luaL_ref ensures the uniqueness of
the key it returns. You can retrieve an object referred by reference
r by calling lua_rawgeti(L, t, r) (see lua_rawgeti()).
Function luaL_unref (see luaL_unref()) frees a reference and
its associated object.
nil, luaL_ref returns the
constant LUA_REFNIL. The constant LUA_NOREF is guaranteed to be
different from any reference returned by luaL_ref.
luaL_Reg
typedef struct luaL_Reg {
const char *name;
lua_CFunction func;
} luaL_Reg;luaL_register (see
luaL_register()). name is the function name and func is a
pointer to the function. Any array of luaL_Reg must end with a
sentinel entry in which both name and func are NULL.
luaL_register()
void luaL_register (lua_State *L,
const char *libname,
const luaL_Reg *l);libname equal to NULL, it simply registers all
functions in the list l (see luaL_Reg) into the table on
the top of the stack.
libname, luaL_register creates a new
table t, sets it as the value of the global variable libname, sets
it as the value of package.loaded[libname], and registers on it all
functions in the list l. If there is a table in
package.loaded[libname] or in variable libname, reuses this table
instead of creating a new one.
luaL_typename()
const char *luaL_typename (lua_State *L, int idx);idx.
luaL_typerror()
int luaL_typerror (lua_State *L, int narg, const char *tname);location : bad argument narg to 'func' ( tname
expected, got rt )
location is produced by luaL_where (see
luaL_where()), func is the name of the current function, and
rt is the type name of the actual argument.
luaL_unref()
void luaL_unref (lua_State *L, int t, int ref);ref from the table at index t (see
luaL_ref()). The entry is removed from the table, so that the
referred object can be collected. The reference ref is also freed to
be used again.
ref is LUA_NOREF or LUA_REFNIL, luaL_unref does nothing.
luaL_where()
void luaL_where (lua_State *L, int lvl);lvl in the call stack. Typically this string has
the following format:
chunkname:currentline:
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., sort).
lua-openlibs
To have access to these libraries, the C host program should call the
luaL_openlibs function, which opens all standard libraries (see
luaL_openlibs()). Alternatively, the host program can open the libraries
individually by calling luaopen_base (for the basic library),
luaopen_package (for the package library), luaopen_string (for the string
library), luaopen_table (for the table library), luaopen_math (for the
mathematical library), luaopen_io (for the I/O and the Operating System
libraries), and luaopen_debug (for the debug library). These functions are
declared in lualib.h and should not be called directly: you must call them
like any other Lua C function, e.g., by using lua_call (see lua_call()).
{v} [, {message}]) assert()
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!"
{opt} [, {arg}]) collectgarbage()
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 lua-gc).
"setstepmul" sets {arg} /100 as the new value for thestep
multiplier` of the collector (see lua-gc).
{filename}) dofile()
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).
{message} [, {level}]) error()
Terminates the last protected function called and returns message as
the error message. Function {error} never returns.
{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.
_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.)
{f}) getfenv()
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.
{object}) getmetatable()
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.
{t}) ipairs()
Returns three values: an iterator function, the table {t}, and 0, so
that the construction
for i,v in ipairs(t) do body end
1,t[1]), (2,t[2]), ..., up to the
first integer key absent from the table.
{func} [, {chunkname}]) load()
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.
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.
{filename}]) loadfile()
Similar to load (see load()), but gets the chunk from file
{filename} or from the standard input, if no file name is given.
{string} [, {chunkname}]) loadstring()
Similar to load (see load()), but gets the chunk from the
given {string}.
assert(loadstring(s))(){table} [, {index}]) next()
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.
for or the ipairs() function.)
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.
{t}) pairs()
Returns three values: the next() function, the table {t}, and nil,
so that the construction
for k,v in pairs(t) do body end
{t}.
{f}, {arg1}, {...}) pcall()
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.
{...}) print()
Receives any number of arguments, and prints their values to stdout,
using the tostring 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 (see string.format()).
{v1}, {v2}) rawequal()
Checks whether {v1} is equal to {v2}, without invoking any metamethod.
Returns a boolean.
{table}, {index}) rawget()
Gets the real value of table[index], without invoking any
metamethod. {table} must be a table; {index} may be any value.
{table}, {index}, {value}) rawset()
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.
{table}.
{index}, {...}) select()
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.
{f}, {table}) setfenv()
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.
{f} is 0 setfenv changes the environment of
the running thread. In this case, setfenv returns no values.
{table}, {metatable}) setmetatable()
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.
{table}.
{e} [, {base}]) tonumber()
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.
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 lua-lexical). In other bases,
only unsigned integers are accepted.
{e}) tostring()
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 (see string.format()).
__tostring
If the metatable of {e} has a "__tostring" field, tostring calls
the corresponding value with {e} as argument, and uses the result of
the call as its result.
{v}) lua-type()
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".
{list} [, {i} [, {j}]]) unpack()
Returns the elements from the given table. This function is equivalent
to
return list[i], list[i+1], ..., list[j]{i} is 1 and {j} is the length of the list, as
defined by the length operator (see lua-length).
_VERSION
A global variable (not a function) that holds a string containing the
current interpreter version. The current contents of this string is
"Lua 5.1" .
{f}, {err}) xpcall()
This function is similar to pcall (see 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}.
coroutine. See lua-coroutine for a
general description of coroutines.
{f}) coroutine.create()
Creates a new coroutine, with body {f}. {f} must be a Lua function.
Returns this new coroutine, an object with type "thread".
{co} [, {val1}, {...}]) coroutine.resume()
Starts or continues the execution of coroutine {co}. The first time
you resume a coroutine, it starts running its body. The values {val1},
{...} are passed as arguments to the body function. If the coroutine has
yielded, resume restarts it; the values {val1}, {...} are passed as
the results from the yield.
resume returns true plus
any values passed to yield (if the coroutine yields) or any values
returned by the body function(if the coroutine terminates). If there
is any error, resume returns false plus the error message.
coroutine.running()
Returns the running coroutine, or nil when called by the main
thread.
{co}) coroutine.status()
Returns the status of coroutine {co}, as a string: "running", if the
coroutine is running (that is, it called status); "suspended", if
the coroutine is suspended in a call to yield, or if it has not
started running yet; "normal" if the coroutine is active but not
running (that is, it has resumed another coroutine); and "dead" if
the coroutine has finished its body function, or if it has stopped
with an error.
{f}) coroutine.wrap()
Creates a new coroutine, with body {f}. {f} must be a Lua function.
Returns a function that resumes the coroutine each time it is called.
Any arguments passed to the function behave as the extra arguments to
resume. Returns the same values returned by resume, except the
first boolean. In case of error, propagates the error.
{...}) coroutine.yield()
Suspends the execution of the calling coroutine. The coroutine cannot
be running a C function, a metamethod, or an iterator. Any arguments
to yield are passed as extra results to resume.
require and module (see require() and module()). Everything else is
exported in a table package.
{name} [, {...}]) module()
Creates a module. If there is a table in package.loaded[name], this
table is the module. Otherwise, if there is a global table t with
the given name, this table is the module. Otherwise creates a new
table t and sets it as the value of the global {name} and the value
of package.loaded[name]. This function also initializes t._NAME
with the given name, t._M with the module (t itself), and
t._PACKAGE with the package name (the full module name minus last
component; see below). Finally, module sets t as the new
environment of the current function and the new value of
package.loaded[name], so that require() returns t.
{name} is a compound name (that is, one with components separated
by dots), module creates (or reuses, if they already exist) tables
for each component. For instance, if {name} is a.b.c, then module
stores the module table in field c of field b of global a.
options after the module name,
where each option is a function to be applied over the module.
{modname}) require()
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.
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 below).
require first uses a dynamic link facility
to link the application with the library. Then it tries to find a C
function inside this 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 prefix up to (and including) the
first hyphen is removed. For instance, if the module name is
a.v1-b.c, the function name will be luaopen_b_c.
require finds neither a Lua library nor a C library for a module,
it calls the all-in-one loader. This loader 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.
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].
require signals an error.
package.cpath
The path used by require to search for a C loader.
package.cpath in the same way it
initializes the Lua path package.path, using the environment
variable LUA_CPATH (plus another default path defined in
luaconf.h).
package.loaded()
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, require simply returns the value stored there.
{libname}, {funcname}) package.loadlib()
Dynamically links the host program with the C library {libname}.
Inside this library, looks for a function {funcname} and returns this
function as a C function. (So, {funcname} must follow the protocol
(see lua_CFunction)).
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 extension. {funcname} must be the exact name exported by the
C library (which may depend on the C compiler and linker used).
dlfcn standard).
package.path
The path used by require to search for a Lua loader.
LUA_PATH or with a default path defined in
luaconf.h, if the environment variable is not defined. Any ";;" in
the value of the environment variable is replaced by the default path.
templates separated by semicolons. For each
template, require will change each interrogation mark in the
template by filename, which is modname with each dot replaced by a
"directory separator" (such as "/" in Unix); then it will try to
load the resulting file name. So, for instance, if the Lua path is
"./?.lua;./?.lc;/usr/local/?/init.lua"
foo will try to load the
files ./foo.lua, ./foo.lc, and /usr/local/foo/init.lua, in that
order.
package.preload()
A table to store loaders for specific modules (see require()).
{module}) package.seeall()
Sets a metatable for {module} with its __index field referring to
the global environment, so that this module inherits values from the
global environment. To be used as an option to function {module}.
string.
It also sets a metatable for strings where the __index field points to the
string table. Therefore, you can use the string functions in object-oriented
style. For instance, string.byte(s, i) can be written as s:byte(i).
{s} [, {i} [, {j}]]) string.byte()
Returns the internal numerical codes of the characters s[i],
s[i+1],..., s[j]. The default value for {i} is 1; the default
value for {j} is {i}.
{...}) string.char()
Receives zero or more integers. Returns a string with length equal to
the number of arguments, in which each character has the internal
numerical code equal to its correspondent argument.
{function}) string.dump()
Returns a string containing a binary representation of the given
function, so that a later loadstring() on this string returns a
copy of the function. {function} must be a Lua function without
upvalues.
{s}, {pattern} [, {init} [, {plain}]]) string.find()
Looks for the first match of {pattern} in the string {s}. If it finds
a match, then {find} returns the indices of {s} where this occurrence
starts and ends; otherwise, it returns nil. A third, optional
numerical argument {init} specifies where to start the search; its
default value is 1 and may be negative. A value of {true} as a fourth,
optional argument {plain} turns off the pattern matching facilities,
so the function does a plain "find substring" operation, with no
characters in {pattern} being considered "magic". Note that if {plain}
is given, then {init} must be given as well.
{formatstring}, {...}) string.format()
Returns a formatted version of its variable number of arguments
following the description given in its first argument (which must be a
string). The format string follows the same rules as the printf
family of standard C functions. The only differences are that the
options/modifiers *, l, L, n, p, and h are not supported
and that there is an extra option, q. The q option formats a
string in a form suitable to be safely read back by the Lua
interpreter: the string is written between double quotes, and all
double quotes, newlines, embedded zeros, and backslashes in the string
are correctly escaped when written. For instance, the call
string.format('%q', 'a string with "quotes" and \n new line')"a string with \"quotes\" and \
new line"c, d, E, e, f, g, G, i, o, u, X, and
x all expect a number as argument, whereas q and s expect a
string.
{s}, {pattern}) string.gmatch()
Returns an iterator function that, each time it is called, returns the
next captures from {pattern} over string {s}.
{pattern} specifies no captures, then the whole match is produced
in each call.
s = "hello world from Lua"
for w in string.gmatch(s, "%a+") do
print(w)
end{s}, printing one per
line. The next example collects all pairs key=value from the given
string into a table:
t = {}
s = "from=world, to=Lua"
for k, v in string.gmatch(s, "(%w+)=(%w+)") do
t[k] = v
end{s}, {pattern}, {repl} [, {n}]) string.gsub()
Returns a copy of {s} in which all occurrences of the {pattern} have
been replaced by a replacement string specified by {repl}, which may
be a string, a table, or a function. gsub also returns, as its
second value, the total number of substitutions made.
{repl} is a string, then its value is used for replacement. The
character % works as an escape character: any sequence in {repl} of
the form %n, with {n} between 1 and 9, stands for the value of the
{n} -th captured substring (see below). The sequence %0 stands for
the whole match. The sequence %% stands for a single %.
{repl} is a table, then the table is queried for every match, using
the first capture as the key; if the pattern specifies no captures,
then the whole match is used as the key.
{repl} is a function, then this function is called every time a
match occurs, with all captured substrings passed as arguments, in
order; if the pattern specifies no captures, then the whole match is
passed as a sole argument.
false or nil, then there is no replacement
(that is, the original match is kept in the string).
{n} limits the maximum number of
substitutions to occur. For instance, when {n} is 1 only the first
occurrence of pattern is replaced.
x = string.gsub("hello world", "(%w+)", "%1 %1")
--> x="hello hello world world"
x = string.gsub("hello world", "%w+", "%0 %0", 1)
--> x="hello hello world"
x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
--> x="world hello Lua from"
x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
--> x="home = /home/roberto, user = roberto"
x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
return loadstring(s)()
end)
--> x="4+5 = 9"
local t = {name="lua", version="5.1"}
x = string.gsub("$name%-$version.tar.gz", "%$(%w+)", t)
--> x="lua-5.1.tar.gz"{s}) string.len()
Receives a string and returns its length. The empty string "" has
length 0. Embedded zeros are counted, so "a\000b\000c" has length 5.
{s}) string.lower()
Receives a string and returns a copy of this string with all uppercase
letters changed to lowercase. All other characters are left unchanged.
The definition of what an uppercase letter is depends on the current
locale.
{s}, {pattern} [, {init}]) string.match()
Looks for the first match of {pattern} in the string {s}. If it
finds one, then match returns the captures from the pattern;
otherwise it returns nil. If {pattern} specifies no captures, then
the whole match is returned. A third, optional numerical argument
{init} specifies where to start the search; its default value is 1 and
may be negative.
{s}, {n}) string.rep()
Returns a string that is the concatenation of {n} copies of the string
{s}.
{s}, {i} [, {j}]) string.sub()
Returns the substring of {s} that starts at {i} and continues until
{j}; {i} and {j} may be negative. If {j} is absent, then it is assumed
to be equal to -1 (which is the same as the string length). In
particular, the call string.sub(s,1,j) returns a prefix of {s} with
length {j}, and string.sub(s,-i) returns a suffix of {s} with length
{i}.
{s}) string.upper()
Receives a string and returns a copy of that string with all lowercase
letters changed to uppercase. All other characters are left unchanged.
The definition of what a lowercase letter is depends on the current
locale.
x (where x is not one of the magic characters ^$()%.[]*+-?)
represents the character x itself.
. (a dot) represents all characters.
%a represents all letters.
%c represents all control characters.
%d represents all digits.
%l represents all lowercase letters.
%p represents all punctuation characters.
%s represents all space characters.
%u represents all uppercase letters.
%w represents all alphanumeric characters.
%x represents all hexadecimal digits.
%z represents the character with representation 0.
%x (where x is any non-alphanumeric character) represents the
character x. This is the standard way to escape the magic
characters. Any punctuation character (even the non-magic) can be
preceded by a % when used to represent itself in a pattern.
[set] represents the class which is the union of all characters in
set. A range of characters may be specified by separating the end
characters of the range with a -. All classes %x described
above may also be used as components in set. All other characters
in set represent themselves. For example, [%w_] (or [_%w])
represents all alphanumeric characters plus the underscore, [0-7]
represents the octal digits, and [0-7%l%-] represents the octal
digits plus the lowercase letters plus the - character.
[%a-z] or [a-%%] have no meaning.
[^set] represents the complement of set, where set is interpreted
as above.
%a, %c, etc.), the
corresponding uppercase letter represents the complement of the class. For
instance, %S represents all non-space characters.
[a-z] may not be equivalent to %l.
*, which matches 0 or more
repetitions of characters in the class. These repetition items will
always match the longest possible sequence;
+, which matches 1 or more
repetitions of characters in the class. These repetition items will
always match the longest possible sequence;
-, which also matches 0 or
more repetitions of characters in the class. Unlike *, these
repetition items will always match the shortest possible sequence;
?, which matches 0 or 1
occurrences of a character in the class;
%n, for n between 1 and 9; such item matches a substring equal to the
n -th captured string (see below);
%bxy, where x and y are two distinct characters; such item matches
strings that start with x, end with y, and where the x and y
are balanced. This means that, if one reads the string from left to
right, counting +1 for an x and -1 for a y, the ending y is the first
y where the count reaches 0. For instance, the item %b() matches
expressions with balanced parentheses.
^ at the beginning of a pattern
anchors the match at the beginning of the subject string. A $ at the end of
a pattern anchors the match at the end of the subject string. At other
positions, ^ and $ have no special meaning and represent themselves.
"(a*(.)%w(%s*))", the part of the string matching "a*(.)%w(%s*)" is stored
as the first capture (and therefore has number 1); the character matching .
is captured with number 2, and the part matching %s* has number 3.
() captures the current string position
(a number). For instance, if we apply the pattern "()aa()" on the
string "flaaap", there will be two captures: 3 and 5.
%z instead.
table.
{table} [, {sep} [, {i} [, {j}]]]) table.concat()
Given an array where all elements are strings or numbers, returns
table[i]..sep..table[i+1] ... sep..table[j]. The default value for
{sep} is the empty string, the default for {i} is 1, and the default
for {j} is the length of the table. If {i} is greater than {j},
returns the empty string.
{table}, {f}) table.foreach()
Executes the given {f} over all elements of {table}. For each element,
{f} is called with the index and respective value as arguments. If {f}
returns a non-`nil` value, then the loop is broken, and this value is
returned as the final value of table.foreach.
{table}, {f}) table.foreachi()
Executes the given {f} over the numerical indices of {table}. For each
index, {f} is called with the index and respective value as arguments.
Indices are visited in sequential order, from 1 to n, where n is
the length of the table. If {f} returns a non-`nil` value, then the
loop is broken and this value is returned as the result of
table.foreachi.
{table}, [{pos},] {value}) table.insert()
Inserts element {value} at position {pos} in {table}, shifting up
other elements to open space, if necessary. The default value for
{pos} is n+1, where n is the length of the table (see
lua-length), so that a call table.insert(t,x) inserts x
at the end of table t.
{table}) table.maxn()
Returns the largest positive numerical index of the given table, or
zero if the table has no positive numerical indices. (To do its job
this function does a linear traversal of the whole table.)
{table} [, {pos}]) table.remove()
Removes from {table} the element at position {pos}, shifting down
other elements to close the space, if necessary. Returns the value of
the removed element. The default value for {pos} is n, where n is
the length of the table (see lua-length), so that a call
table.remove(t) removes the last element of table t.
{table} [, {comp}]) table.sort()
Sorts table elements in a given order, in-place, from table[1] to
table[n], where n is the length of the table (see lua-length).
If {comp} is given, then it must be a function that receives two table
elements, and returns true when the first is less than the second (so
that not comp(a[i+1],a[i]) will be true after the sort). If {comp}
is not given, then the standard Lua operator < is used instead.
not stable, that is, elements considered equal by the
given order may have their relative positions changed by the sort.
math.
{x}, {y}) math.atan2()
Returns the arc tangent of x/y (in radians), but uses the signs of
both parameters to find the quadrant of the result. (It also handles
correctly the case of {y} being zero.)
{x}) math.frexp()
Returns m and e such that x = m * 2^e, e is an integer and the
absolute value of m is in the range [0.5, 1) (or zero when {x} is
zero).
math.huge
The value HUGE_VAL, a value larger than or equal to any other
numerical value.
{x}) math.modf()
Returns two numbers, the integral part of {x} and the fractional part
of {x}.
math.pi
The value of pi.
{x}, {y}) math.pow()
Returns x^y. (You can also use the expression x^y to compute this
value.)
{m} [, {n}]]) math.random()
This function is an interface to the simple pseudo-random generator
function rand provided by ANSI C. (No guarantees can be given for
its statistical properties.)
[0,1). When called with a number {m}, math.random
returns a pseudo-random integer in the range [1, m]. When called
with two numbers {m} and {n}, math.random returns a pseudo-random
integer in the range [m, n].
{x}) math.randomseed()
Sets {x} as the "seed" for the pseudo-random generator: equal seeds
produce equal sequences of numbers.
{x}) math.sqrt()
Returns the square root of {x}. (You can also use the expression
x^0.5 to compute this value.)
io. When using explicit file descriptors, the operation io.open returns
a file descriptor and then all operations are supplied as methods of the file
descriptor.
io also provides three predefined file descriptors with their usual
meanings from C: io.stdin, io.stdout, and io.stderr.
nil on failure (plus an
error message as a second result) and some value different from nil on
success.
{file}]) io.close()
Equivalent to file:close. Without a {file}, closes the default
output file.
io.flush()
Equivalent to file:flush over the default output file.
{file}]) io.input()
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 sets this file handle as the default input file.
When called without parameters, it returns the current default input
file.
{filename}]) io.lines()
Opens the given file name in read mode and returns an iterator
function that, each time it is called, returns a new line from the
file. Therefore, the construction
for line in io.lines(filename) do body end
nil (to finish the loop) and
automatically closes the file.
io.lines() (without a file name) is equivalent to
io.input():lines(); that is, it iterates over the lines of the
default input file. In this case it does not close the file when the
loop ends.
{filename} [, {mode}]) io.open()
This function opens a file, in the mode specified in the string
{mode}. It returns a new file handle, or, in case of errors, nil
plus an error message.
{mode} string can be any of the following:
"r" read mode (the default);
"w" write mode;
"a" append mode;
"r+" update mode, all previous data is preserved;
"w+" update mode, all previous data is erased;
"a+" append update mode, previous data is preserved, writing is
only allowed at the end of file.
{mode} string may also have a b at the end, which is needed in
some systems to open the file in binary mode. This string is exactly
what is used in the standard C function fopen.
{prog} [, {mode}]) io.popen()
Starts program {prog} in a separated process and returns a file handle
that you can use to read data from this program (if {mode} is "r",
the default) or to write data to this program (if {mode} is "w").
io.tmpfile()
Returns a handle for a temporary file. This file is opened in update
mode and it is automatically removed when the program ends.
{obj}) io.type()
Checks whether {obj} is a valid file handle. Returns the string
"file" if {obj} is an open file handle, "closed file" if {obj} is
a closed file handle, or nil if {obj} is not a file handle.
file:close()
Closes file. Note that files are automatically closed when their
handles are garbage collected, but that takes an unpredictable amount
of time to happen.
file:flush()
Saves any written data to file.
file:lines()
Returns an iterator function that, each time it is called, returns a
new line from the file. Therefore, the construction
for line in file:lines() do body end
io.lines, this
function does not close the file when the loop ends.)
{...}) file:read()
Reads the file file, according to the given formats, which specify
what to read. For each format, the function returns a string (or a
number) with the characters read, or nil if it cannot read data with
the specified format. When called without formats, it uses a default
format that reads the entire next line (see below).
"*n" reads a number; this is the only format that returns a
number instead of a string.
"*a" reads the whole file, starting at the current position. On
end of file, it returns the empty string.
"*l" reads the next line (skipping the end of line), returning
nil on end of file. This is the default format.
number reads a string with up to that number of characters,
returning nil on end of file. If number is zero, it reads
nothing and returns an empty string, or nil on end of file.
{whence}] [, {offset}]) file:seek()
Sets and gets the file position, measured from the beginning of the
file, to the position given by {offset} plus a base specified by the
string {whence}, as follows:
"set": base is position 0 (beginning of the file);
"cur": base is current position;
"end": base is end of file;
seek returns the final file position,
measured in bytes from the beginning of the file. If this function
fails, it returns nil, plus a string describing the error.
{whence} is "cur", and for {offset} is 0.
Therefore, the call file:seek() returns the current file position,
without changing it; the call file:seek("set") sets the position to
the beginning of the file (and returns 0); and the call
file:seek("end") sets the position to the end of the file, and
returns its size.
{mode} [, {size}]) file:setvbuf()
Sets the buffering mode for an output file. There are three available
modes:
"no" no buffering; the result of any output operation appears
immediately.
"full" full buffering; output operation is performed only when
the buffer is full (or when you explicitly flush the file
(see io.flush()).
"line" line buffering; output is buffered until a newline is
output or there is any input from some special files (such as
a terminal device).
{size} specifies the size of the buffer, in
bytes. The default is an appropriate size.
{...}) file:write()
Writes the value of each of its arguments to file. The arguments
must be strings or numbers. To write other values, use tostring
tostring() or string.format string.format() before
write.
os.
os.clock()
Returns an approximation of the amount in seconds of CPU time used by
the program.
{format} [, {time}]]) os.date()
Returns a string or a table containing date and time, formatted
according to the given string {format}.
{time} argument is present, this is the time to be formatted
(see the os.time function os.time() for a description of this
value). Otherwise, date formats the current time.
{format} starts with !, then the date is formatted in
Coordinated Universal Time. After this optional character, if {format}
is the string "*t", then date returns a table with the following
fields: year (four digits), month (1-12), day (1-31), hour
(0-23), min (0-59), sec (0-61), wday (weekday, Sunday is 1),
yday (day of the year), and isdst (daylight saving flag, a
boolean).
{format} is not "*t", then date returns the date as a string,
formatted according to the same rules as the C function strftime.
date returns a reasonable date and
time representation that depends on the host system and on the current
locale (that is, os.date() is equivalent to os.date("%c")).
{t2}, {t1}) os.difftime()
Returns the number of seconds from time {t1} to time {t2}. In POSIX,
Windows, and some other systems, this value is exactly t2 - t1 .
{command}]) os.execute()
This function is equivalent to the C function system. It passes
{command} to be executed by an operating system shell. It returns a
status code, which is system-dependent. If {command} is absent, then
it returns nonzero if a shell is available and zero otherwise.
{code}]) os.exit()
Calls the C function exit, with an optional {code}, to terminate the
host program. The default value for {code} is the success code.
{varname}) os.getenv()
Returns the value of the process environment variable {varname}, or
nil if the variable is not defined.
{filename}) os.remove()
Deletes the file with the given name. Directories must be empty to be
removed. If this function fails, it returns nil, plus a string
describing the error.
{oldname}, {newname}) os.rename()
Renames file named {oldname} to {newname}. If this function fails, it
returns nil, plus a string describing the error.
{locale} [, {category}]) os.setlocale()
Sets the current locale of the program. {locale} is a string
specifying a locale; {category} is an optional string describing which
category to change: "all", "collate", "ctype", "monetary",
"numeric", or "time"; the default category is "all". The
function returns the name of the new locale, or nil if the request
cannot be honored.
{table}]) os.time()
Returns the current time when called without arguments, or a time
representing the date and time specified by the given table. This
table must have fields year, month, and day, and may have fields
hour, min, sec, and isdst (for a description of these fields,
see the os.date function os.date()).
time can be used only as an argument to date and difftime.
os.tmpname()
Returns a string with a file name that can be used for a temporary
file. The file must be explicitly opened before its use and explicitly
removed when no longer needed.
debug table. All
functions that operate over a thread have an optional first argument which is
the thread to operate over. The default is always the current thread.
debug.debug()
Enters an interactive mode with the user, running each string that the
user enters. Using simple commands and other debug facilities, the
user can inspect global and local variables, change their values,
evaluate expressions, and so on. A line containing only the word
cont finishes this function, so that the caller continues its
execution.
debug.debug are not lexically nested within
any function, and so have no direct access to local variables.
debug.getfenv()
Returns the environment of object {o}.
{thread}]) debug.gethook()
Returns the current hook settings of the thread, as three values: the
current hook function, the current hook mask, and the current hook
count (as set by the debug.sethook function).
{thread},] {function} [, {what}]) debug.getinfo()
Returns a table with information about a function. You can give the
function directly, or you can give a number as the value of
{function}, which means the function running at level {function} of
the call stack of the given thread: level 0 is the current function
(getinfo itself); level 1 is the function that called getinfo; and
so on. If {function} is a number larger than the number of active
functions, then getinfo returns nil.
lua_getinfo (see lua_getinfo()), with the string {what}
describing which fields to fill in. The default for {what} is to get
all information available, except the table of valid lines. If
present, the option f adds a field named func with the function
itself. If present, the option L adds a field named activelines
with the table of valid lines.
debug.getinfo(1,"n").name returns the
name of the current function, if a reasonable name can be found, and
debug.getinfo(print) returns a table with all available information
about the print function.
{thread},] {level}, {local}) debug.getlocal()
This function returns the name and the value of the local variable
with index {local} of the function at level {level} of the stack. (The
first parameter or local variable has index 1, and so on, until the
last active local variable.) The function returns nil if there is no
local variable with the given index, and raises an error when called
with a {level} out of range. (You can call debug.getinfo
debug.getinfo() to check whether the level is valid.)
( (open parentheses) represent
internal variables (loop control variables, temporaries, and C
function locals).
{object}) debug.getmetatable()
Returns the metatable of the given {object} or nil if it does not
have a metatable.
debug.getregistry()
Returns the registry table (see lua-registry).
{func}, {up}) debug.getupvalue()
This function returns the name and the value of the upvalue with index
{up} of the function {func}. The function returns nil if there is no
upvalue with the given index.
{object}, {table}) debug.setfenv()
Sets the environment of the given {object} to the given {table}.
Returns {object}.
{thread},] {hook}, {mask} [, {count}]) debug.sethook()
Sets the given function as a hook. The string {mask} and the number
{count} describe when the hook will be called. The string mask may
have the following characters, with the given meaning:
"c" : The hook is called every time Lua calls a function;
"r" : The hook is called every time Lua returns from a function;
"l" : The hook is called every time Lua enters a new line of
code.
{count} different from zero, the hook is called after every
{count} instructions.
debug.sethook turns off the hook.
"call", "return" (or"tail
return"`), "line", and "count". For line events, the hook also
gets the new line number as its second parameter. Inside a hook, you
can call getinfo with level 2 to get more information about the
running function (level 0 is the getinfo function, and level 1 is
the hook function), unless the event is "tail return". In this case,
Lua is only simulating the return, and a call to getinfo will return
invalid data.
{thread},] {level}, {local}, {value}) debug.setlocal()
This function assigns the value {value} to the local variable with
index {local} of the function at level {level} of the stack. The
function returns nil if there is no local variable with the given
index, and raises an error when called with a {level} out of range.
(You can call getinfo to check whether the level is valid.)
Otherwise, it returns the name of the local variable.
{object}, {table}) debug.setmetatable()
Sets the metatable for the given {object} to the given {table} (which
can be nil).
{func}, {up}, {value}) debug.setupvalue()
This function assigns the value {value} to the upvalue with index {up}
of the function {func}. The function returns nil if there is no
upvalue with the given index. Otherwise, it returns the name of the
upvalue.
{thread},] [{message} [,{level}]]) debug.traceback()
Returns a string with a traceback of the call stack. An optional
{message} string is appended at the beginning of the traceback. An
optional {level} number tells at which level to start the traceback
(default is 1, the function calling traceback).