The Lua language (v5.1)
Reserved identifiers and comments
| and break do else elseif | end | false for function if in |
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| 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 string; escape sequences are ignored. |
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| \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 (up to 3 digits) |
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). |
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| 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. |
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| 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 ) body [return values] end anonymous function assigned to variable f |
| function ( [args, ] ... ) body [return values] end variable argument list, in body accessed as ... |
| function t.name ( args ) body [return values] end shortcut for t.name = function ... |
| function obj:name ( args ) body [return values] end object function, gets obj as additional first 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) |
Metatable fields (for tables and userdata)
| setmetatable (t, mt) sets mt as metatable for t, unless t's metatable has a __metatable field, and returns t |
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| 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 |
| __add, __sub | sets handler h(a, b) for '+' and for binary '-' | __mul, __div | sets handler h(a, b) for '*' and for '/' |
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| __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 (userdata) |
| __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, v) 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 l ibrary [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. |
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| 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. Returns function f if f ~= 0. |
| _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 |
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| 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) |
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| 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!"] |
| select (index, ...) | returns the arguments after argument number index or (if index is "#") the total number of arguments it received after index |
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| 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 |
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| 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 l ibrary [package] |
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| 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 corout ine l ibrary [corout ine] |
| 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 l ibrary [ table] |
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| 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 mathemat ical l ibrary [math]
Basic operations
| 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 |
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| 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 |
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| 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 |
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| math.ldexp (x, y) returns x * (2 ^ y) with x = normalized fraction, y = exponent of 2 |
Pseudo-random numbers
Note: string indexes extend from 1 to #string, or from end of string if negative (index -1 refers to the last character).
Note: the string library sets a metatable for strings where the __index field points to the string table. String functions can be used in object-oriented style, e.g. string.len(s) can be written s:len(); literals have to be enclosed in parentheses, e.g. ("xyz"):len().
| 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. |
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| math.randomseed (n) | sets a seed n for random sequence (same seed = same sequence) |
The st ring l ibrary [st ring]
Basic operations
| string.len (s) returns the length of string s, including embedded zeros (see also # operator) |
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| 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 [, j]]) | returns the platform-dependent numerical code (e.g. ASCII) of characters s[i], s[i+1], ···, s[j]. The default value for i is 1; the default value for j is i. |
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| 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) |
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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 field types |
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| %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 [+ |
| %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 |
| - left-justifies within field_width [default: right-justify] |
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| + 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 |
| n | puts at least n (<100) characters, pad with blanks |
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| 0n | puts at least n (<100) characters, left-pad with zeros |
| .n | puts at least n (<100) digits for integers; rounds to n decimals for floating-point; puts no more than n (<100) characters for strings. |
| string.format("results: %d, %d", 13, 27) results: 13, 27 |
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| 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") |
| 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. |
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| 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: all] 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 ] |
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| 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) |
| %bxy 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 |
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| () stores current string position as capture |
Pattern character classes
| . | any character | | |
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| %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 |
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| 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 l ibrary [ 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. |
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| 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 |
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| 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 operat ing system l ibrary [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 l ibrary [debug]
Basic functions
| debug.debug () | enters interactive debugging shell (type cont to exit); local variables cannot be accessed directly. |
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| 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 |
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| 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 |
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| 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) |
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| -e stats executes the Lua statements in the literal string stats, can be used multiple times on the same line |
| -l filename 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 |
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| 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. |
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| _PROMPT[2] | contain the prompt for interactive mode; can be changed by assigning a new value. |
The compi ler
Command line syntax
luac [options] [filenames]
Options
| - compiles from standard input |
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| -l produces a listing of the compiled bytecode |
| -o filename 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, 2008 and 2009. Comments, praise or blame please to the lua-l mailing list.
This reference card can be used and distributed according to the terms of the Lua 5.1 license.