Lua 5.1 short reference

Contents

· The Lua language · · The base library · · Modules and the package library · · The coroutine library · · The table library · · The mathematical library · · The string library · · The I/O library · · The operating system library · · The debug library · · The stand-alone interpreter · · The compiler ·

The Lua language (v5.1)

· Reserved identifiers and comments

and | break | do | else | elseif | end | false | for | function | if | in
local | nil | not | or | repeat | return | then | true | until | while |
-- ... | comment to end of line | --[=[ ]=] | multi line comment (zero or multiple '=' are valid)
_X is "reserved" (by convention) for constants (with X being any sequence of uppercase letters) | #! | usual Unix shebang; Lua ignores whole first line if this starts the line.

· Types (the string values are the possible results of base library function type())

"nil" | "boolean" | "number" | "string" | "table" | "function" | "thread" | "userdata"

Note: for type boolean, nil and false count as false; everything else is true (including 0 and "").

· Strings and escape sequences

'...' and "..." | string delimiters; interpret escapes. | [=[...]=] | multi line strings; escape sequences are ignored.
\a bell | \b backspace | \f form feed | \n newline | \r return | \t horiz. tab | \v vert. tab
\\ backslash | \" d. quote | \' quote | \[ sq. bracket | \] sq. bracket | \ddd decimal |

· Operators, decreasing precedence

^ (right associative, math library required)
not | # (length of strings and tables) | - (unary)
* | / | %
+ | -
.. (string concatenation, right associative)
< | > | <= | >= | ~= | ==
and (stops on false or nil , returns last evaluated value)
or (stops on true (not false or nil ), returns last evaluated value)

· Assignment and coercion

a = 5 b= "hi" local a = a | simple assignment; variables are not typed and can hold different types. Local variables are lexically scoped; their scope begins after the full declaration (so that local a = 5).
a, b, c = 1, 2, 3 | multiple assignments are supported
a, b = b, a | swap values: right hand side is evaluated before assignment takes place
a, b = 4, 5, "6" | excess values on right hand side ("6") are evaluated but discarded
a, b = "there" | for missing values on right hand side nil is assumed
a = nil | destroys a ; its contents are eligible for garbage collection if unreferenced.
a = z | if z is not defined it is nil , so nil is assigned to a (destroying it)
a = "3" + "2" | numbers expected, strings are converted to numbers (a = 5)
a = 3 .. 2 | strings expected, numbers are converted to strings (a = "32")

· Control structures

do block end | block; introduces local scope.
if exp then block { elseif exp then block } [ else block ] end | conditional execution
while exp do block end | loop as long as exp is true
repeat block until exp | exits when exp becomes true; exp is in loop scope.
for var = start , end [ , step ] do block end | numerical for loop; var is local to loop.
for vars in iterator do block end | iterator based for loop; vars are local to loop.
break | exits loop; must be last statement in block.

· Table constructors

t = {} | creates an empty table and assigns it to t
t = {"yes", "no", "?"} | simple array; elements are t[1] , t[2] , t[3] .
t = { [1] = "yes", [2] = "no", [3] = "?" } | same as above, but with explicit fields
t = {[-900] = 3, [+900] = 4} | sparse array with just two elements (no space wasted)
t = {x=5, y=10} | hash table, fields are t["x"] , t["y"] (or t.x , t.y )
t = {x=5, y=10; "yes", "no"} | mixed, fields/elements are t.x , t.y , t[1] , t[2]
t = {msg = "choice", {"yes", "no", "?"}} | tables can contain others tables as fields

· Function definition

function name ( args ) body [ return values ] end | defines function and assigns to global variable name
local function name ( args ) body [ return values ] end | defines function as local to chunk
f = function ( args ) | anonymous function assigned to variable f
function ( [ args , ] ... ) body [ return values ] end | variable argument list, in body accessed as ...
function t . name | shortcut for t . name = function ...
function obj : name | object function, gets obj as extra argument self

· Function call

f (x) | simple call, possibly returning one or more values
f "hello" | shortcut for f("hello")
f 'goodbye' | shortcut for f('goodbye')
f [[see you soon]] | shortcut for f([[see you soon]])
f {x = 3, y = 4} | shortcut for f({x = 3, y = 4})
t.f (x) | calling a function assigned to field f of table t
x:move (2, -3) | object call: shortcut for x.move(x, 2, -3) , x will be assigned to self

· Metatable operations (base library required)

setmetatable (t, mt) | sets mt as metatable for t , unless t 's metatable has a __metatable field
getmetatable (t) | returns __metatable field of t 's metatable or t 's metatable or nil
rawget (t, i) | gets t[i] of a table without invoking metamethods
rawset (t, i, v) | sets t[i] = v on a table without invoking metamethods
rawequal (t1, t2) | returns boolean (t1 == t2) without invoking metamethods

· Metatable fields (for tables and userdata)

__add, __sub | sets handler h(a, b) for ' + ' and for binary ' - ' | __mul, __div | sets handler h(a, b) for ' * ' and for ' / '
__mod | set handler h(a, b) for '%' | __pow | sets handler h(a, b) for ' ^ '
__unm | sets handler h(a) for unary ' - ' | __len | sets handler h(a) for the # operator
__concat | sets handler h(a, b) for '..' | __eq | sets handler h(a, b) for ' == ', ' ~= '
__lt | sets handler h(a, b) for ' < ', ' > ' and possibly ' <= ', ' >= ' (if no __le ) | __le | sets handler h(a, b) for ' <= ', ' >= '
__index | sets handler h(t, k) for access to non-existing field | __newindex | sets handler h(t, k) for assignment to non-existing field
__call | sets handler h(f, ...) for function call (using the object as a function) | __tostring | sets handler h(a) to convert to string, e.g. for print()
__gc | sets finalizer h(ud) for userdata (has to be set from C) | __mode | table mode: 'k' = weak keys; 'v' = weak values; 'kv' = both.
__metatable | sets value to be returned by getmetatable() |  |

The base library [no prefix]

· Environment and global variables

getfenv ([f]) | if f is a function, returns its environment; if f is a number, returns the environment of function at level f (1 = current [default], 0 = global); if the environment has a field __fenv , returns that instead.
setfenv (f, t) | sets environment for function f or function at level f (0 = current thread); if the original environment has a field __fenv , raises an error.
_G | global variable whose value is the global environment (that is, _G._G == _G )
_VERSION | global variable containing the interpreter's version (e.g. "Lua 5.1" )

· Loading and executing

require (pkgname) | loads a package, raises error if it can't be loaded
dofile ([filename]) | loads and executes the contents of filename [default: standard input]; returns its returned values.
load (func [, chunkname]) | loads a chunk (with chunk name set to name ) using function func to get its pieces; returns compiled chunk as function (or nil and error message).
loadfile (filename) | loads file filename ; return values like load() .
loadstring (s [, name]) | loads string s (with chunk name set to name ); return values like load() .
pcall (f [, args ]) | calls f() in protected mode; returns true and function results or false and error message.
xpcall (f, h) | as pcall() but passes error handler h instead of extra args; returns as pcall() but with the result of h() as error message, if any.

· Simple output and error feedback

print ( args ) | prints each of the passed args to stdout using tostring() (see below)
error (msg [, n]) | terminates the program or the last protected call (e.g. pcall() ) with error message msg quoting level n [default: 1, current function]
assert (v [, msg]) | calls error(msg) if v is nil or false [default msg : "assertion failed!" ]

· Information and conversion

select (index, ...) | returns the arguments after argument number index or (if index is "#") the total number of arguments it received after index
type (x) | returns the type of x as a string (e.g. "nil" , "string" ); see Types above.
tostring (x) | converts x to a string, using t 's metatable's __tostring if available
tonumber (x [, b]) | converts string x representing a number in base b [2..36, default: 10] to a number, or nil if invalid; for base 10 accepts full format (e.g. "1.5e6").
unpack (t) | returns t[1] .. t[n] (n = #t ) as separate values

· Iterators

ipairs (t) | returns an iterator getting index, value pairs of array t in numerical order
pairs (t) | returns an iterator getting key, value pairs of table t in an unspecified order
next (t [, inx]) | if inx is nil [default] returns first index, value pair of table t ; if inx is the previous index returns next index, value pair or nil when finished.

· Garbage collection

collectgarbage (opt [, arg]) | generic interface to the garbage collector; opt defines function performed.

Modules and the package library [package]

module (name, ...) | creates module name. If there is a table in package.loaded[name] , this table is the module. Otherwise, if there is a global table name , this table is the module. Otherwise creates a new table and sets it as the value of the global name and the value of package.loaded[name] . Optional arguments are functions to be applied over the module.
package.loadlib (lib, func) | loads dynamic library lib (e.g. .so or .dll) and returns function func ( or nil and error message)
package.path, package.cpath | contains the paths used by require() to search for a Lua or C loader, respectively
package.loaded | a table used by require to control which modules are already loaded (see module)
package.preload | a table to store loaders for specific modules (see require)
package.seeall (module) | sets a metatable for module with its __index field referring to the global environment

The coroutine library [coroutine]

coroutine.create (f) | creates a new coroutine with Lua function f() as body and returns it
coroutine.resume (co, args ) | starts or continues running coroutine co , passing args to it; returns true (and possibly values) if co calls coroutine.yield() or terminates or false and an error message.
coroutine.yield ( args ) | suspends execution of the calling coroutine (not from within C functions, metamethods or iterators); any args become extra return values of coroutine.resume() .
coroutine.status (co) | returns the status of coroutine co : either "running" , "suspended" or "dead"
coroutine.running () | returns the running coroutine or nil when called by the main thread
coroutine.wrap (f) | creates a new coroutine with Lua function f as body and returns a function; this function will act as coroutine.resume() without the first argument and the first return value, propagating any errors.

The table library [table]

table.insert (t, [i,] v) | inserts v at numerical index i [default: after the end] in table t
table.remove (t [, i]) | removes element at numerical index i [default: last element] from table t ; returns the removed element or nil on empty table.
table.maxn (t) | returns the largest positive numerical index of table t or zero if t has no positive indices
table.sort (t [, cf]) | sorts (in place) elements from t[1] to # t , using compare function cf(e1, e2) [default: ' < ']
table.concat (t [, s [, i [, j]]]) | returns a single string made by concatenating table elements t[i] to t[j] [default: i =1 , j = #t ] separated by string s ; returns empty string if no elements exist or i > j .

The mathematical library [math]

· Basic operations

math.abs (x) | returns the absolute value of x
math.mod (x, y) | returns the remainder of x / y as a rounded-down integer, for y ~= 0
math.floor (x) | returns x rounded down to the nearest integer
math.ceil (x) | returns x rounded up to the nearest integer
math.min ( args ) | returns the minimum value from the args received
math.max ( args ) | returns the maximum value from the args received

· Exponential and logarithmic

math.sqrt (x) | returns the square root of x , for x >= 0
math.pow (x, y) | returns x raised to the power of y , i.e. x ^ y ; if x < 0, y must be integer.
__pow (x, y) | global function added by the math library to make operator ' ^ ' work
math.exp (x) | returns e (base of natural logs) raised to the power of x , i.e. e^ x
math.log (x) | returns the natural logarithm of x , for x >= 0
math.log10 (x) | returns the base-10 logarithm of x , for x >= 0

· Trigonometrical

math.deg (a) | converts angle a from radians to degrees
math.rad (a) | converts angle a from degrees to radians
math.pi | constant containing the value of pi
math.sin (a) | returns the sine of angle a (measured in radians)
math.cos (a) | returns the cosine of angle a (measured in radians)
math.tan (a) | returns the tangent of angle a (measured in radians)
math.asin (x) | returns the arc sine of x in radians, for x in [-1, 1]
math.acos (x) | returns the arc cosine of x in radians, for x in [-1, 1]
math.atan (x) | returns the arc tangent of x in radians
math.atan2 (y, x) | similar to math.atan(y / x) but with quadrant and allowing x = 0

· Splitting on powers of 2

math.frexp (x) | splits x into normalized fraction and exponent of 2 and returns both
math.ldexp (x, y) | returns x * (2 ^ y ) with x = normalized fraction, y = exponent of 2

· Pseudo-random numbers

math.random ([n [, m]) | returns a pseudo-random number in range [0, 1] if no arguments given; in range [1, n ] if n is given, in range [ n , m ] if both n and m are passed.
math.randomseed (n) | sets a seed n for random sequence (same seed = same sequence)

The string library [string]

· Basic operations

string.len (s) | returns the length of string s , including embedded zeros (see also # operator)
string.sub (s, i [, j]) | returns the substring of s from position i to j [default: -1] inclusive
string.rep (s, n) | returns a string made of n concatenated copies of string s
string.upper (s) | returns a copy of s converted to uppercase according to locale
string.lower (s) | returns a copy of s converted to lowercase according to locale

· Character codes

string.byte (s [, i]) | returns the platform-dependent numerical code (e.g. ASCII) of character at position i [default: 1] in string s , or nil if i is invalid
string.char ( args ) | returns a string made of the characters whose platform-dependent numerical codes are passed as args

· Function storage

string.dump (f) | returns a binary representation of function f() , for later use with loadstring() ( f() must be a Lua function with no upvalues)

Note: string indexes extend from 1 to #string, or from end of string if negative (index -1 refers to the last character).

· Formatting

string.format (s [, args ]) | returns a copy of s where formatting directives beginning with ' % ' are replaced by the value of arguments args , in the given order (see Formatting directives below)

· Formatting directives for string.format

% [ flags ] [ field_width ] [ . precision ] type

· Formatting field types

%d | decimal integer
%o | octal integer
%x | hexadecimal integer, uppercase if %X
%f | floating-point in the form [-]nnnn.nnnn
%e | floating-point in exp. Form [-]n.nnnn e [+|-]nnn, uppercase if %E
%g | floating-point as %e if exp. < -4 or >= precision, else as %f ; uppercase if %G .
%c | character having the (system-dependent) code passed as integer
%s | string with no embedded zeros
%q | string between double quotes, with all special characters escaped
%% | ' % ' character

· Formatting flags

- | left-justifies within field_width [default: right-justify]
+ | prepends sign (only applies to numbers)
( space ) | prepends sign if negative, else blank space
# | adds "0x" before %x , force decimal point for %e , %f , leaves trailing zeros for %g

· Formatting field width and precision

n | puts at least n characters, pad with blanks
0n | puts at least n characters, left-pad with zeros
.n | puts at least n digits for integers; rounds to n decimals for floating-point; puts no more than n characters for strings.

· Formatting examples

string.format("results: %d, %d", 13, 27) | results: 13, 27
string.format("<%5d>", 13) | < 13>
string.format("<%-5d>", 13) | <13 >
string.format("<%05d>", 13) | <00013>
string.format("<%06.3d>", 13) | < 013>
string.format("<%f>", math.pi) | <3.141593>
string.format("<%e>", math.pi) | <3.141593e+00>
string.format("<%.4f>", math.pi) | <3.1416>
string.format("<%9.4f>", math.pi) | < 3.1416>
string.format("<%c>", 64) | <@>
string.format("<%.4s>", "goodbye") | <good>
string.format("%q", [[she said "hi"]]) | "she said \"hi\""

· Finding, replacing, iterating (for the Patterns see below)

string.find (s, p [, i [, d]]) | returns first and last position of pattern p in string s , or nil if not found, starting search at position i [default: 1]; returns captures as extra results. If d is true, treat pattern as plain string.
string.gmatch (s, p) | returns an iterator getting next occurrence of pattern p (or its captures) in string s as substring(s) matching the pattern.
string.gsub (s, p, r [, n]) | returns a copy of s with up to n [default: 1] occurrences of pattern p (or its captures) replaced by r if r is a string ( r can include references to captures in the form % n ). If r is a function r() is called for each match and receives captured substrings; it should return the replacement string. If r is a table, the captures are used as fields into the table. The function returns the number of substitutions made as second result.
string.match (s, p [, i]) | returns captures of pattern p in string s (or the whole match if p specifies no captures) or nil if p does not match s ; starts search at position i [default: 1].

· Patterns and pattern items

General pattern format: pattern_item [ pattern_items ]
cc | matches a single character in the class cc (see Pattern character classes below)
cc * | matches zero or more characters in the class cc ; matchest longest sequence (greedy).
cc - | matches zero or more characters in the class cc ; matchest shortest sequence (non-greedy).
cc + | matches one or more characters in the class cc ; matchest longest sequence (greedy).
cc ? | matches zero or one character in the class cc
% n | matches the n -th captured string ( n = 1..9, see Pattern captures )
%b xy | matches the balanced string from character x to character y (e.g. %b() for nested parentheses)
^ | anchors pattern to start of string, must be the first item in the pattern
$ | anchors pattern to end of string, must be the last item in the pattern

· Captures

( pattern ) | stores substring matching pattern as capture %1 .. %9 , in order of opening parentheses
() | stores current string position as capture

· Pattern character classes

. | any character |  |
%a | any letter | %A | any non-letter
%c | any control character | %C | any non-control character
%d | any digit | %D | any non-digit
%l | any lowercase letter | %L | any non-(lowercase letter)
%p | any punctuation character | %P | any non-punctuation character
%s | any whitespace character | %S | any non-whitespace character
%u | any uppercase letter | %U | any non-(uppercase letter)
%w | any alphanumeric character | %W | any non-alphanumeric character
%x | any hexadecimal digit | %X | any non-(hexadecimal digit)
%z | the byte value zero | %Z | any non-zero character
% x | if x is a symbol the symbol itself | x | if x not in ^$()%.[]*+-? the character itself
[ set ] | any character in any of the given classes; can also be a range [ c1 - c2 ] , e.g. [a-z]. | [ ^ set ] | any character not in set

· Pattern examples

string.find("Lua is great!", "is") | 5 | 6
string.find("Lua is great!", "%s") | 4 | 4
string.gsub("Lua is great!", "%s", "-") | Lua-is-great! | 2
string.gsub("Lua is great!", "[%s%l]", "*") | L***********! | 11
string.gsub("Lua is great!", "%a+", "*") | * * *! | 3
string.gsub("Lua is great!", "(.)", "%1%1") | LLuuaa iiss ggrreeaatt!! | 13
string.gsub("Lua is great!", "%but", "") | L! | 1
string.gsub("Lua is great!", "^.-a", "LUA") | LUA is great! | 1
string.gsub("Lua is great!", "^.-a", function(s) return string.upper(s) end) | LUA is great! | 1

The I/O library [io]

· Complete I/O

io.open (fn [, m]) | opens file with name fn in mode m : "r" = read [default], "w" = write", "a" = append, "r+" = update-preserve, "w+" = update-erase, "a+" = update-append (add trailing "b" for binary mode on some systems); returns a file object (a userdata with a C handle).
file :close () | closes file
file :read ( formats ) | returns a value from file for each of the passed formats : "*n" = reads a number, "*a" = reads the whole file as a string from current position (returns "" at end of file), "*l" = reads a line ( nil at end of file) [default], n = reads a string of up to n characters ( nil at end of file)
file :lines () | returns an iterator function for reading file line by line; the iterator does not close the file when finished.
file :write ( values ) | writes each of the values (strings or numbers) to file , with no added separators. Numbers are written as text, strings can contain binary data (in this case, file may need to be opened in binary mode on some systems).
file :seek ([p] [, of]) | sets the current position in file relative to p ("set" = start of file [default], "cur" = current, "end" = end of file) adding offset of [default: zero]; returns new current position in file .
file :flush () | flushes any data still held in buffers to file

· Simple I/O

io.input ([file]) | sets file as default input file; file can be either an open file object or a file name; in the latter case the file is opened for reading in text mode. Returns a file object, the current one if no file given; raises error on failure.
io.output ([file]) | sets file as default output file (the current output file is not closed); file can be either an open file object or a file name; in the latter case the file is opened for writing in text mode. Returns a file object, the current one if no file given; raises error on failure.
io.close ([file]) | closes file (a file object) [default: closes the default output file]
io.read ( formats ) | reads from the default input file, usage as file:read()
io.lines ([fn]) | opens the file with name fn for reading and returns an iterator function to read line by line; the iterator closes the file when finished. If no fn is given, returns an iterator reading lines from the default input file.
io.write ( values ) | writes to the default output file, usage as file:write()
io.flush () | flushes any data still held in buffers to the default output file

· Standard files and utility functions

io.stdin, io.stdout, io.stderr | predefined file objects for stdin, stdout and stderr streams
io.popen ([prog [, mode]]) | starts program prog in a separate process and returns a file handle that you can use to read data from (if mode is "r", default) or to write data to (if mode is "w")
io.type (x) | returns the string "file" if x is an open file, "closed file" if x is a closed file or nil if x is not a file object
io.tmpfile () | returns a file object for a temporary file (deleted when program ends)

Note: unless otherwise stated, the I/O functions return nil and an error message on failure; passing a closed file object raises an error instead.

The operating system library [os]

· System interaction

os.execute (cmd) | calls a system shell to execute the string cmd as a command; returns a system-dependent status code.
os.exit ([code]) | terminates the program returning code [default: success]
os.getenv (var) | returns a string with the value of the environment variable var or nil if no such variable exists
os.setlocale (s [, c]) | sets the locale described by string s for category c : "all", "collate", "ctype", "monetary", "numeric" or "time" [default: "all"]; returns the name of the locale or nil if it can't be set.
os.remove (fn) | deletes the file fn ; in case of error returns nil and error description.
os.rename (of, nf) | renames file of to nf ; in case of error returns nil and error description.
os.tmpname () | returns a string usable as name for a temporary file; subject to name conflicts, use io.tmpfile() instead.

· Date/time

os.clock () | returns an approximation of the amount in seconds of CPU time used by the program
os.time ([tt]) | returns a system-dependent number representing date/time described by table tt [default: current]. tt must have fields year , month , day ; can have fields hour , min , sec , isdst (daylight saving, boolean). On many systems the returned value is the number of seconds since a fixed point in time (the "epoch").
os.date ([fmt [, t]]) | returns a table or a string describing date/time t (should be a value returned by os.time() [default: current date/time]), according to the format string fmt [default: date/time according to locale settings]; if fmt is "*t" or "!*t", returns a table with fields year (yyyy), month (1..12), day (1..31), hour (0..23), min (0..59), sec (0..61), wday (1..7, Sunday = 1), yday (1..366), isdst (true = daylight saving), else returns the fmt string with formatting directives beginning with ' % ' replaced according to Time formatting directives (see below). In either case a leading "!" requests UTC (Coordinated Universal Time).
os.difftime (t2, t1) | returns the difference between two values returned by os.time()

· Time formatting directives (most used, portable features):

%c | date/time (locale) |  |
%x | date only (locale) | %X | time only (locale)
%y | year (nn) | %Y | year (yyyy)
%j | day of year (001..366) |  |
%m | month (01..12) |  |
%b | abbreviated month name (locale) | %B | full name of month (locale)
%d | day of month (01..31) |  |
%U | week number (01..53), Sunday-based | %W | week number (01..53), Monday-based
%w | weekday (0..6), 0 is Sunday |  |
%a | abbreviated weekday name (locale) | %A | full weekday name (locale)
%H | hour (00..23) | %I | hour (01..12)
%p | either AM or PM |  |
%M | minute (00..59) |  |
%S | second (00..61) |  |
%Z | time zone name, if any |  |

The debug library [debug]

· Basic functions

debug.debug () | enters interactive debugging shell (type cont to exit); local variables cannot be accessed directly.
debug.getinfo (f [, w]) | returns a table with information for function f or for function at level f [1 = caller], or nil if invalid level (see Result fields for getinfo below); characters in string w select one or more groups of fields [default: all] (see Options for getinfo below).
debug.getlocal (n, i) | returns name and value of local variable at index i (from 1, in order of appearance) of the function at stack level n (1= caller); returns nil if i is out of range, raises error if n is out of range.
debug.getupvalue (f, i) | returns name and value of upvalue at index i (from 1, in order of appearance) of function f ; returns nil if i is out of range.
debug.traceback ([msg]) | returns a string with traceback of call stack, prepended by msg
debug.setlocal (n, i, v) | assigns value v to the local variable at index i (from 1, in order of appearance) of the function at stack level n (1= caller); returns nil if i is out of range, raises error if n is out of range.
debug.setupvalue (f, i, v) | assigns value v to the upvalue at index i (from 1, in order of appearance) of function f ; returns nil if i is out of range.
debug.sethook ([h, m [, n]]) | sets function h as hook, called for events given in string (mask) m : "c" = function call, "r" = function return, "l" = new code line; also, a number n will call h() every n instructions; h() will receive the event type as first argument: "call", "return", "tail return", "line" (line number as second argument) or "count"; use debug.getinfo(2) inside h() for info (not for "tail_return").
debug.gethook () | returns current hook function, mask and count set with debug.sethook()

Note: the debug library functions are not optimised for efficiency and should not be used in normal operation.

· Result fields for debug.getinfo

source | name of file (prefixed by '@') or string where the function was defined
short_src | short version of source , up to 60 characters
linedefined | line of source where the function was defined
what | "Lua" = Lua function, "C" = C function, "main" = part of main chunk
name | name of function, if available, or a reasonable guess if possible
namewhat | meaning of name : "global", "local", "method", "field" or ""
nups | number of upvalues of the function
func | the function itself

· Options for debug.getinfo (character codes for argument w)

n | returns fields name and namewhat | l | returns field currentline
f | returns field func | u | returns field nup
S | returns fields source , short_src , what and linedefined |  |

The stand-alone interpreter

· Command line syntax

lua [ options ] [ script [ arguments ]]

· Options

- | loads and executes script from standard input (no args allowed)
-e | executes the Lua statements in the literal string stats , can be used multiple times on the same line
-l | requires filename (loads and executes if not already done)
-i | enters interactive mode after loading and executing script
-v | prints version information
-- | stops parsing options

· Recognized environment variables

LUA_INIT | if this holds a string in the form @filename loads and executes filename , else executes the string itself
LUA_PATH | defines search path for Lua modules, with "?" replaced by the module name
LUA_CPATH | defines search path for dynamic libraries (e.g. .so or .dll files), with "?" replaced by the module name
_PROMPT[2] | set the prompts for interactive mode

· Special Lua variables

arg | nil if no arguments on the command line, else a table containing command line arguments starting from arg[1] while # arg is the number of arguments ; arg[0] holds the script name as given on the command line; arg[-1] and lower indexes contain the fields of the command line preceding the script name.
_PROMPT[2] | contain the prompt for interactive mode; can be changed by assigning a new value.

The compiler

· Command line syntax

luac [ options ] [ filenames ]

· Options

- | compiles from standard input
-l | produces a listing of the compiled bytecode
-o | sends output to filename [default: luac.out ]
-p | performs syntax and integrity checking only, does not output bytecode
-s | strips debug information; line numbers and local names are lost.
-v | prints version information
-- | stops parsing options

Note: compiled chunks are portable between machines having the same word size.

Lua is a language designed and implemented by Roberto Ierusalimschy, Luiz Henrique de Figueiredo and Waldemar Celes; for details see lua.org. Drafts of this reference card (for Lua 5.0) were produced by Enrico Colombini <erix@erix.it> in 2004 and updated by Thomas Lauer <thomas.lauer@gmail.com> in 2007. Comments, praise or blame please to the lua-l mailing list.