Extension:Scribunto/Lua reference manual

This manual documents Lua as it is used in MediaWiki with the Scribunto extension. Some parts are derived from the Lua 5.1 reference manual, which is available under the MIT license.

Getting started
On a MediaWiki wiki with Scribunto enabled, create a page with a title starting with "Module:", for example "Module:Bananas". Into this new page, copy the following text:

Save that, then on another (non-module) page, write:

Except that you should replace "Bananas" with whatever you called your module. This will call the "hello" function exported from that module. The will be replaced with the text that the function returned, in this case, "Hello, world!"

It's generally a good idea to invoke Lua code from the context of a template. This means that from the perspective of a calling page, the syntax is independent of whether the template logic is implemented in Lua or in wikitext. It also avoids the introduction of additional complex syntax into the content namespace of a wiki.

Module structure
The module itself must return a table containing the functions that may be called by. Generally, as shown above, a local variable is declared holding a table, functions are added to this table, and the table is returned at the end of the module code.

Any functions that are not added to this table, whether local or global, will not be accessible by, but globals might be accessible from other modules loaded using. It is generally good style for the module to declare all functions and variables local.

Returning text
The module function should usually return a single string; whatever values are returned will be passed through tostring and then concatenated with no separator. This string is incorporated into the wikitext as the result of the.

At this point in the page parse, templates have already been expanded, parser functions and extension tags have already been processed, and pre-save transforms (e.g. signature tilde expansion and the pipe trick) have already happened. Therefore the module cannot use these features in its output text. For example, if a module returns, the page will read "Hello, world!  ".

On the other hand, subst is handled at an earlier stage of processing, so with  only other attempted substitutions will be processed. Since the failed substitution will remain in the wikitext, they will then be processed on the next edit. This should generally be avoided.

Module documentation
Scribunto allows modules to be documented by automatically associating the module with a wikitext documentation page; by default, the "/doc" subpage of the module is used for this purpose and is transcluded above the module source code on the module page. For example, the documentation for "Module:Bananas" would be at "Module:Bananas/doc".

This can be configured using the following MediaWiki-namespace messages:
 * scribunto-doc-page-name: Sets the name of the page used for documentation. The name of the module (without the Module: prefix) is passed as . If in the module namespace, the pages specified here will be interpreted as wikitext rather than Lua source and may not be used with  . The default is "Module:$1/doc", i.e. the /doc subpage of the module. Note that parser functions and other brace expansion may not be used in this message.
 * scribunto-doc-page-does-not-exist: Message displayed when the doc page does not exist. The name of the page is passed as . The default is empty.
 * scribunto-doc-page-show: Message displayed when the doc page does exist. The name of the page is passed as . The default is to transclude the documentation page.
 * scribunto-doc-page-header: Header displayed when viewing the documentation page itself. The name of the module (with Module: prefix) being documented is passed as . The default simply displays a short explanation in italics.

Note that modules cannot be directly categorized and cannot have interwiki links directly added. These could be placed on the documentation page inside  tags, where they will be applied to the module when the documentation page is transcluded onto the module page.

Tokens
Names (also called identifiers) in Lua can be any string of letters, digits, and underscores, not beginning with a digit. Names are case-sensitive; "foo", "Foo", and "FOO" are all different names.

The following keywords are reserved and may not be used as names:  Names starting with an underscore followed by uppercase letters are reserved for internal Lua global variables.
 * and
 * break
 * do
 * else
 * elseif
 * end
 * false
 * for
 * function
 * if
 * in
 * local
 * nil
 * not
 * or
 * repeat
 * return
 * then
 * true
 * until
 * while

Other tokens are: 
 * &#x25;
 * &#x3a;
 * &#x3b;
 * ]
 * }
 * &#x3a;
 * &#x3b;
 * ]
 * }
 * &#x3a;
 * &#x3b;
 * ]
 * }
 * &#x3b;
 * ]
 * }
 * ]
 * }
 * ]
 * }
 * ]
 * }
 * }
 * }
 * }

Comments
A comment starts with a  anywhere outside a string. If the  is immediately followed by an opening long bracket, the comment continues to the corresponding closing long bracket; otherwise the comment runs to the end of the current line.

Data types
Lua is a dynamically-typed language, which means that variables and function arguments have no type, only the values assigned to them. All values carry a type.

Lua has eight basic data types, however only six are relevant to the Scribunto extension. The  function will return the type of a value.

The  function will convert a value to a string. The  function will convert a value to a number if possible, and otherwise will return nil. There are no explicit functions to convert a value to other data types.

Numbers are automatically converted to strings when used where a string is expected, e.g. when used with the concatenation operator. Strings recognized by  are automatically converted to numbers when used with arithmetic operators. When a boolean value is expected, all values other than nil and false are considered to be true.

nil
"nil" is the data type of, which exists to represent the absence of a value. Nil may not be used as a key in a table, and there is no difference between an unassigned table key and a key assigned a nil value.

When converted to a string, the result is "nil". When converted to boolean, nil is considered false. returns "nil".

boolean
Boolean values are  and.

When converted to a string, the result is "true" or "false". Unlike many other languages, boolean values may not be directly converted to numbers. And unlike many other languages, only false and nil are considered false for boolean conversion; the number 0 and the empty string are both considered true.

string
Lua strings are considered a series of 8-bit bytes; it is up to the application to interpret them in any particular encoding.

String literals may be delimited by either single or double quotes ( or  ); like JavaScript and unlike PHP, there is no difference between the two. The following escape sequences are recognized: '\a' (bell), '\b' (backspace), '\f' (form feed), '\n' (newline), '\r' (carriage return), '\t' (horizontal tab), '\v' (vertical tab), '\\' (backslash), '\"' (double quote), and '\&#x27;' (single quote). A literal newline may also be included in a string by preceding it with a backslash. Bytes may also be specified using an escape sequence '\ddd', where ddd is the decimal value of the byte in the range 0–255. To include Unicode characters using escape sequences, the individual bytes for the UTF-8 encoding must be specified; in general, it will be more straightforward to enter the Unicode characters directly.

Literal strings can also be defined using long brackets. An opening long bracket consists of an opening square bracket followed by zero or more equal signs followed by another opening square bracket, e.g.,  , or. The opening long bracket must be matched by the corresponding closing long bracket, e.g.,  , or. Strings delimited by long brackets do not interpret escape sequences. As a special case, if an opening long bracket is immediately followed by a newline then the newline is not included in the string.

Note that all strings are considered true when converted to boolean. This is unlike most other languages, where the empty string is usually considered false.

number
Lua has only one numeric type, which is typically represented internally as a double-precision floating-point value. In this format, integers between -9007199254740992 and 9007199254740992 may be represented exactly, while higher and lower numbers will suffer from round-off error.

Numbers are specified using a period as a decimal separator and without grouping separators, e.g.  . Numbers may also be represented using E notation without spaces, e.g. ,  , or. Integers may also be specified in hexadecimal notation using a  prefix, e.g..

Although NaN and positive and negative infinities are correctly stored and handled, Lua does not provide corresponding literals. The constant  is positive infinity, as is a division such as , and a division such as   may be used to quickly generate a NaN.

Note that all numbers are considered true when converted to boolean. This is unlike most other languages, where the number 0 is usually considered false. When converted to a string, finite numbers are represented in decimal, possibly in E notation; NaN is "nan" or "-nan"; and infinities are "inf" or "-inf".

table
Lua tables are associative arrays, much like PHP arrays and JavaScript objects.

Tables are created using curly braces. The empty table is. To populate fields on creation, a comma- and/or semicolon-separated list of field specifiers may be included in the braces. These take any of several forms:
 * uses the (first) value of expression1 as the key and the (first) value of expression2 as the value.
 * is equivalent to
 * is roughly equivalent to, where i is an integer starting at 1 and incrementing with each field specification of this form. If this is the last field specifier and the expression has multiple values, all values are used; otherwise only the first is kept.

The fields in a table are accessed using bracket notation, e.g. . String keys that are also valid names may also be accessed using dot notation, e.g.   is equivalent to. Calling a function that is a value in the table may use colon notation, e.g., which is equivalent to.

A sequence is a table with non-nil values for all positive integers from 1 to N and no value (nil) for all positive integers greater than N. Many Lua functions operate only on sequences, and ignore non-positive-integer keys.

Unlike PHP or JavaScript, however, any value except nil and NaN may be used as a key and no type conversion is performed. These are all valid and distinct:

Similarly, any value except nil may be stored as a value in a table. Storing nil is equivalent to deleting the key from the table, and accessing any key that has not been set will result in a nil value.

Note that tables are never implicitly copied in Lua; if a table is passed as an argument to the function and the function manipulates the keys or values in the table, those changes will be visible in the caller.

When converted to a string, the usual result is "table" but may be overridden using the __tostring metamethod. Even the empty table is considered true as a boolean.

function
Functions in Lua are first-class values: they may be created anonymously, passed as arguments, assigned to variables, and so on.

Functions are created using the  keyword, and called using parentheses. Syntactic sugar is available for named functions, local functions, and functions that act like member functions to a table. See Function declarations and Function calls below for details.

Lua functions are closures, meaning that they maintain a reference to the scope in which they are declared and can access and manipulate variables in that scope.

Like tables, if a function is assigned to a different variable or passed as an argument to another function, it is still the same underlying "function object" that will be called.

When converted to a string, the result is "function".

Unsupported types
The userdata type is used to hold opaque values for extensions to Lua written in other languages; for example, a userdata might be used to hold a C pointer or struct. To allow for use of Scribunto in hosting environments where custom-compiled code is not allowed, no such extensions are used.

The thread type represents the handles for coroutines, which are not available in Scribunto's sandbox.

Metatables
Every table may have an associated table known as a metatable. The fields in the metatable are used by some operators and functions to specify different or fallback behavior for the table. The metatable for a table may be accessed using the getmetatable function, and set with the setmetatable function.

When being accessed for their meta functions, metatable fields are accessed as if with rawget.

Metatable fields that affect the table itself are:
 * __index : This is used when a table access  would return nil. If the value of this field is a table, the access will be repeated in that table, i.e.   (which may invoke that table's metatable's __index). If the value of this field is a function, the function will be called as  . The rawget function bypasses this metamethod.
 * __newindex : This is used when assigning a key to a table  where   would return nil. If the value of this field is a table, the assignment will be repeated in that table, i.e.   (which may invoke that table's metatable's __newindex). If the value of this field is a function, the function will be called as  . The rawset function bypasses this metamethod.
 * __call : This is used when function call syntax is used on a table, . The value must be a function, which is called as something like.
 * __mode : This is used to make tables holding weak references. The value must be a string. By default, any value that is used as a key or as a value in a table will not be garbage collected. But if this metafield contains the letter 'k', keys may be garbage collected if there are no non-weak references, and if it contains 'v' values may be; in either case, both the corresponding key and value are removed from the table. Note that behavior is undefined if this field is altered after the table is used as a metatable.

Other metatable fields include: † For binary operators, Lua looks first at the left argument's metatable (if any) then the right's when looking for a metamethod to use. ‡ For relational operators, the metamethod is only used if the same function is specified in both arguments' metatables. Different anonymous functions, even with identical body and closure, may not be considered the same. * __metatable affects both getmetatable and setmetatable
 * __add†
 * __sub†
 * __mul†
 * __div†
 * __mod†
 * __pow†
 * __unm
 * __concat†
 * __eq‡
 * __lt‡
 * __le‡
 * __pairs
 * __ipairs
 * __metatable*
 * __tostring

Note: In Lua, all strings also share a single metatable, in which __index refers to the  table. This metatable is not accessible in Scribunto, nor is the referenced  table; the string table available to modules is a copy.

Variables
Variables are places that store values. There are three kinds of variables in Lua: global variables, local variables, and table fields.

A name represents a global or local variable (or a function argument, which is just a kind of local variable). Variables are assumed to be global unless explicitly declared as local using the  keyword. Any variable that has not been assigned a value is considered to have a nil value.

Global variables are stored in a standard Lua table called an environment; this table is often available as the global variable. It is possible to set a metatable for this global variable table; the __index and __newindex metamethods will be called for accesses of and assignments to global variables just as they would for accesses of and assignments to fields in any other table.

The environment for a function may be accessed using the getfenv function and changed using the setfenv function; in Scribunto, these functions are severely restricted if they are available at all.

Local variables are lexically scoped; see Local variable declarations for details.

Expressions
An expression is something that has values: literals (numbers, strings, true, false, nil), anonymous function declarations, table constructors, variable references, function calls, the vararg expression, expressions wrapped in parentheses, unary operators applied to expressions, and expressions combined with binary operators.

Most expressions have one value; function calls and the vararg expression can have any number. Note that wrapping a function call or vararg expression in parentheses will lose all except the first value.

Expression lists are comma-separated lists of expressions. All except the last expression are forced to one value (dropping additional values, or using nil if the expression has no values); all values from the last expression are included in the values of the expression list.

The expression lists in Lua is in fact a very lightweight type of tables, except that they are not true objects, but they are created temporarily within control structures: they have no methods, no accessible type, and no associative index (dictionnary of keys) and their scope is limited to a single control structure.

Arithmetic operators
Lua supports the usual arithmetic operators: addition, subtraction, multiplication, division, modulo, exponentiation, and negation.

When all operands are numbers or strings for which tonumber returns non-nil, the operations have their usual meaning.

If either operand is a table with an appropriate metamethod, the metamethod will be called.

Relational operators
The relational operators in Lua are,  ,  ,  ,  , and. The result of a relational operator is always a boolean.

Equality first compares the types of its operands; if they are different, the result is false. Then it compares the values: nil, boolean, number, and string are compared in the expected manner. Functions are equal if they refer to the exact same function object;  will return false, as it is comparing two different anonymous functions. Tables are by default compared in the same manner, but this may be changed using the __eq metamethod.

Inequality is the exact negation of equality.

For the ordering operators, if both are numbers or both are strings, they are compared directly. Next, metamethods are checked: If the necessary metamethods are not available, an error is raised.
 * uses __lt
 * uses __le if available, or if __lt is available then it is considered equivalent to
 * is considered equivalent to
 * is considered equivalent to

Logical operators
The logical operators are,  , and. All use the standard interpretation where nil and false are considered false and anything else is considered true.

For, if the left operand is considered false then it is returned and the second operand is not evaluated; otherwise the second operand is returned.

For, if the left operand is considered true then it is returned and the second operand is not evaluated; otherwise the second operand is returned.

For, the result is always true or false.

Note that  and   short circuit. For example,  will only call   if   returns false or nil as its first value.

Concatenation operator
The concatenation operator is two dots, used as. If both operands are numbers or strings, they are converted to strings and concatenated. Otherwise if a __concat metamethod is available, it is used. Otherwise, an error is raised.

Note that Lua strings are immutable and Lua does not provide any sort of "string builder", so a loop that repeatedly does  will have to create a new string for each iteration and eventually garbage-collect the old strings. If many strings need concatenating, it may be faster to use string.format or to insert all the strings into a sequence and use table.concat at the end.

Length operator
The length operator is, used as. If  is a string, it returns the length in bytes. If  is a sequence table, it returns the length of the sequence.

If  is a table that is not a sequence, the   may return any value N such that a[N] is not nil and a[N+1] is nil, even if there are non-nil values at higher indexes. For example,

Operator precedence
Lua's operator precedence, from highest to lowest:


 * not # - (negation)
 * + - (subtraction)
 * and
 * or
 * and
 * or
 * and
 * or

Within a precedence level, most binary operators are left-associative, i.e.  is interpreted as. Exponentiation and concatenation are right-associative, i.e.  is interpreted as.

Function calls
Lua function calls look like those in most other languages: a name followed by a list of arguments in parentheses:

func( expression-list )

As is usual with expression lists in Lua, the last expression in the list may supply multiple argument values.

If the function is called with fewer values in the expression list than there are arguments in the function definition, the extra arguments will have a nil value. If the expression list contains more values than there are arguments, the excess values are discarded. It is also possible for a function to take a variable number of arguments; see Function declarations for details.

Lua also allows direct calling of a function return value, i.e. . If an expression more complex than a variable access is needed to determine the function to be called, a parenthesized expression may be used in place of the variable access.

Lua has syntactic sugar for two common cases. The first is when a table is being used as an object, and the function is to be called as a method on the object. The syntax

table:name( expression-list )

is exactly equivalent to

table.name( table, expression-list )

The second common case is Lua's method of implementing named arguments by passing a table containing the name-to-value mappings as the only positional argument to the function. In this case, the parentheses around the argument list may be omitted. This also works if the function is to be passed a single literal string. For example, the calls

func{ arg1 = exp, arg2 = exp } func"string"

are equivalent to

func( { arg1 = exp, arg2 = exp } ) func( "string" )

These may be combined; the following calls are equivalent:

table:name{ arg1 = exp, arg2 = exp } table.name( table, { arg1 = exp, arg2 = exp } )

Function declarations
The syntax for function declaration looks like this:

function ( var-list ) block end

All variables in var-list are local to the function, with values assigned from the expression list in the function call. Additional local variables may be declared inside the block.

When the function is called, the statements in block are executed after local variables corresponding to var-list are created and assigned values. If a return statement is reached, the block is exited and the values of the function call expression are those given by the return statement. If execution reaches the end of the function's block without encountering a return statement, the result of the function call expression has zero values.

Lua functions are lexical closures. A common idiom is to declare "private static" variables as locals in the scope where the function is declared. For example,

-- This returns a function that adds a number to its argument function makeAdder( n ) return function( x ) -- The variable n from the outer scope is available here to be added to x        return x + n     end end local add5 = makeAdder( 5 ) mw.log( add5( 6 ) ) -- prints 11

A function may be declared to accept a variable number of arguments, by specifying  as the final item in the var-list:

function ( var-list, ... ) block end

Within the block, the varargs expression  may be used, with the result being all the extra values in the function call. For example,

local join = function ( separator, ... ) -- get the extra arguments as a table local args = { ... }    -- get the count of extra arguments, correctly local n = select( '#', ... ) return table.concat( args, separator, 1, n ) end join( ', ', 'foo', 'bar', 'baz' ) -- returns the string "foo, bar, baz"

The select function is designed to work with the varargs expression; in particular,  should be used instead of   to count the number of values in the varargs expression.

Lua provides syntactic sugar to combine function declaration and assignment to a variable; see Function declaration statements for details.

Note that this will not work:  local factorial = function ( n ) if n <= 2 then return n   else return n * factorial( n - 1 ) end end Since the function declaration is processed before the local variable assignment statement is complete, "factorial" inside the function body refers to the (probably undefined) global variable of that name. This problem may be avoided by declaring the local variable first and then assigning it in a subsequent statement, or by using the function declaration statement syntax.

Statements
A statement is the basic unit of execution: one assignment, control structure, function call, variable declaration, etc.

A chunk is a sequence of statements, optionally separated by semicolons. A chunk is basically considered the body of an anonymous function, so it can declare local variables, receive arguments, and return values.

A block is also a sequence of statements, just like a chunk. A block can be delimited to create a single statement:. These may be used to limit the scope of local variables, or to add a  or   in the middle of another block.

Assignments
The variable-list is a comma-separated list of variables; the expression-list is a comma-separated list of one or more expressions. All expressions are evaluated before any assignments are performed, so  will swap the values of a and b.


 * Warning
 * The comma in Lua does not behave at all like in other common languages (such as C, C++, or Java), when they are using it either as an operator in expressions, or as a separator for the declaration of variables and function parameters or within the initializers of declared variables, or in the parameter list of function calls. Its use in Lua assignments does not create a "comma expression" (is which valid as an expression statement in C or C++). The assignments in Lua are not themselves valid expressions (usable in subexpressions), they are only valid as statements within a block or chunk.
 * Also the number of expressions in the expression-list in Lua does not need to match the number of variables in the variable-list. So in the following assignments:
 * , a will be assigned the value 2, and b will be assigned the value nil (this may seem counter-intuitive for programmers using other languages).
 * , all variables in the variable-list will be assigned the value nil (this is explicit for a and implicit for b ).
 * (common in Lua), a will be asssigned the first returned value, and b will be assigned the second returned value if there's one, or nil otherwise.
 * , b may not necessarily be assigned the value 2 if  returns more than one value or a variable number of values: in that case the first returned value will be assigned to a, the second returned value will be assigned to b , the remaining returned values and 2 will be discarded; if the function does not return any value, a will be assigned 2 and b will be assigned nil.
 * Internally, when there's more than one variable in the variable-list, Lua will create a temporary number-indexed array (with a fixed size determined by the number of variables to assign), in which it will successively append the returned values of each expression in the expression-list (they are all evaluated, from left to right). Then Lua will assign each variable of the variable-list from the temporary number-indexed array; if there's not enough values in the temporary number-indexed array, the remaining variables are assigned the value nil ; if there's more values in the temporary number-indexed array than variables in the variables-list, these values in excess are ignored. Finally the temporary number-indexed array is discarded.
 * This internal process is also used in every other Lua statements that use an expression-list, including the initialisation values in local variable declarations, or the bounding values of the  control statement, or for creating the list of values that will be passed as effective parameters in function calls and then initializing the parameter variables within each called function during its evaluation.

To avoid this separation of values returned by a function (a feature expected by some common Lua functions such as pairs, ipairs or next), that function should explictly return a single array containing all values, instead of a list of expressions, and a reference to that array will be assigned to a single variable. The alternative is to create a new array containing the returned values:, and then access its members by their number index (the first value returned by the function call is in   in this example).

When the expression-list contains a static number of expressions, i.e. when they are not the result of calling some function that may return multiple values or a variable number of values, and these expressions do not depend (during their evaluation) on the current value of variables before their assignment, it may be preferable to separate the statements that will assign individual expressions to the relevant variable(s), in order to get more predictable results (the assignments still continue working with the number of values they expect, even if functions are modified later to return more values than what for which they were initially designed).


 * So  is not recommended (unless you are sure that   will always return one value), and should preferably be written as   or as   where the parentheses surrounding both expressions have the effect of discarding all values except the first one returned by each function call (if a function call does not return any value, the evaluation of the expression with surrounding parentheses will give nil ).
 * But the code  is perfectly safe, just as  : the operators in numeric expressions keep only the first value returned by their operands, and if an operand is a function call that does not return any value, the value of that operand will be nil.
 * The only expression that is not a function call and that keeps multiple values during its evaluation is the special varargs expression, valid only within the scope of a function declared with a varargs parameter (if you combine the varargs with other operations or within parentheses, this will force it to be its first value, or nil if the parameter list is empty).
 * So the assignment  depends on the length of the varargs list: a will be assigned the first value in the varargs and b will be assigned the value 2 only if the varargs list contains exactly one parameter value; if the varargs list is empty, a will be assigned the value 2 and b will be assigned the value nil ; if the varargs list contains two or more parameter values, then a and b will be assigned the first two values in the varargs list. The only way to keep all values in the varargs list is to initialize a new array to contain them: , or to use it in other statements that accept an expression list:   (note the surrounding parentheses to also force the values returned by the function call to only one value).

Local variable declarations
Local variables may be declared anywhere within a block or chunk. The first form, without an expression list, declares the variables but does not assign a value so all variables have nil as a value. The second form assigns values to the local variables, as described in Assignments above.

Note that visibility of the local variable begins with the statement after the local variable declaration. So a declaration like  declares a local variable x and assigns it the value of x from the outer scope. The local variable remains in scope until the end of the innermost block containing the local variable declaration.

Control structures
The while statement repeats a block as long as an expression evaluates to a true value.

The repeat statement repeats a block until an expression evaluates to a true value. Local variables declared inside the block may be accessed in the expression.

This first form of the for loop will declare a local variable, and repeat the block for values from exp1 to exp2 adding exp3 on each iteration. Note that exp3 may be omitted entirely, in which case 1 is used, but non-numeric values such as  and   are an error. All expressions are evaluated once before the loop is started.

This form of the for loop is roughly equivalent to

do    local var, limit, step = tonumber( exp1 ), tonumber( exp2 ), tonumber( exp3 ) if not ( var and limit and step ) then error end while ( step > 0 and var <= limit ) or ( step <= 0 and var >= limit ) do        local name = var block var = var + step end end

except that the variables var, limit, and step are not accessible anywhere else. Note that the variable name is local to the block; to use the value after the loop, it must be copied to a variable declared outside the loop.

The second form of the for loop works with iterator functions. As in the first form, the expresssion-list is evaluated only once before beginning the loop.

This form of the for loop is roughly equivalent to

do    local func, static local var = expression-list while true do        local var-list = func( static, var ) var = var1 -- var1 is the first variable in var-list if var == nil then break end block end end

except that again the variables func, static, and var are not accessible anywhere else. Note that the variables in var-list are local to the block; to use them after the loop, they must be copied to variables declared outside the loop.

Often the expression-list is a single function call that returns the three values. If the iterator function can be written so it only depends on the parameters passed into it, that would be the most efficient. If not, Programming in Lua suggests that a closure be preferred to returning a table as the static variable and updating its members on each iteration.

Executes block1 if exp1 returns true, otherwise executes block2 if exp2 returns true, and block3 otherwise. The  portion may be omitted, and the   portion may be repeated or omitted as necessary.

The return statement is used to return values from a function or a chunk (which is just a function). The expression-list is a comma-separated list of zero or more expressions.

Lua implements tail calls: if expression-list consists of exactly one expression which is a function call, the current stack frame will be reused for the call to that function. This has implication for functions that deal with the call stack, such as  and.

The return statement must be the last statement in its block. If for some reason a return is needed in the middle of a block, an explicit block  may be used.

The break statement is used to terminate the execution of a while, repeat, or for loop, skipping to the next statement after the loop.

The break statement must be the last statement in its block. If for some reason a break is needed in the middle of a block, an explicit block  may be used.

Function calls as statements
A function call may be used as a statement; in this case, the function is being called only for any side effects it may have (e.g. mw.log logs values) and any return values are discarded.

Function declaration statements
Lua provides syntactic sugar to make declaring a function and assigning it to a variable more natural. The following pairs of declarations are equivalent

-- Basic declaration function func( var-list ) block end func = function ( var-list ) block end

-- Local function local function func( var-list ) block end local func; func = function ( var-list ) block end

-- Function as a field in a table function table.func( var-list ) block end table.func = function ( var-list ) block end

-- Function as a method in a table function table:func( var-list ) block end table.func = function ( self, var-list ) block end

Note the colon notation here parallels the colon notation for function calls, adding an implicit argument named "self" at the beginning of the arguments list.

Error handling
Errors may be "thrown" using the error and assert functions. To "catch" errors, use pcall or xpcall. Note that certain internal Scribunto errors cannot be caught in Lua code.

Garbage collection
Lua performs automatic memory management. This means that you have to worry neither about allocating memory for new objects nor about freeing it when the objects are no longer needed. Lua manages memory automatically by running a garbage collector from time to time to collect all dead objects (that is, objects that are no longer accessible from Lua) and objects that are only reachable via weak references. All memory used by Lua is subject to automatic management: tables, functions, strings, etc.

Garbage collection happens automatically, and cannot be configured from within Scribunto.

Standard libraries
The standard Lua libraries provide essential services and performance-critical functions to Lua. Only those portions of the standard libraries that are available in Scribunto are documented here.

_G


This variable holds a reference to the current global variable table; the global variable  may also be accessed as. Note, however, that there is nothing special about _G itself; it may be reassigned in the same manner as any other variable:

foo = 1 mw.log( foo ) -- logs "1" _G.foo = 2 mw.log( foo ) -- logs "2" _G = {}      -- _G no longer points to the global variable table _G.foo = 3 mw.log( foo ) -- still logs "2"

The global variable table may be used just like any other table. For example,

-- Call a function whose name is stored in a variable _G[var]

-- Log the names and stringified values of all global variables for k, v in pairs( _G ) do   mw.log( k, v ) end

-- Log the creation of new global variables setmetatable( _G, {    __newindex = function ( t, k, v )          mw.log( "Creation of new global variable '" .. k .. "'" )         rawset( t, k, v )     end } )

_VERSION


A string containing the running version of Lua, e.g. "Lua 5.1".

assert
If  is nil or false, issues an error. In this case,  is used as the text of the error: if nil (or unspecified), the text is "assertion failed!"; if a string or number, the text is that value; otherwise assert itself will raise an error.

If  is any other value, assert returns all arguments including   and.

A somewhat common idiom in Lua is for a function to return a "true" value in normal operation, and on failure return nil or false as the first value and an error message as the second value. Easy error checking can then be implemented by wrapping the call in a call to :

-- This doesn't check for errors local result1, result2, etc = func( ... ) -- This works the same, but does check for errors local result1, result2, etc = assert( func( ... ) )

error
Issues an error, with text.

normally adds some information about the location of the error. If  is 1 or omitted, that information is the location of the call to   itself; 2 uses the location of the call of the function that called error; and so on. Passing 0 omits inclusion of the location information.

getfenv
Note this function may not be available, depending on  in the engine configuration.

Returns an environment (global variable table), as specified by :
 * If 1, nil, or omitted, returns the environment of the function calling . Often this will be the same as _G.
 * Integers 2–10 return the environment of functions higher in the call stack. For example, 2 returns the environment for the function that called the current function, 3 returns the environment for the function calling that function, and so on. An error will be raised if the value is higher than the number of function calls in the stack, or if the targeted stack level returned with a tail call.
 * Passing a function returns the environment that will be used when that function is called.

The environments used by all standard library functions and Scribunto library functions are protected. Attempting to access these environments using  will return nil instead.

getmetatable
Returns the metatable of a table. Any other type will return nil.

If the metatable has a __metatable field, that value will be returned instead of the actual metatable.

ipairs
Returns three values: an iterator function, the table, and 0. This is intended for use in the iterator form of :

for i, v in ipairs( t ) do    block end

This will iterate over the pairs ( 1, t[1] ), ( 2, t[2] ), and so on, stopping when t[i] would be nil.

The standard behavior may be overridden by providing an __ipairs metamethod. If that metamethod exists, the call to ipairs will return the three values returned by  instead.

next
This allows for iterating over the keys in a table. If  is nil or unspecified, returns the "first" key in the table and its value; otherwise, it returns the "next" key and its value. When no more keys are available, returns nil. It is possible to check whether a table is empty using the expression.

Note that the order in which the keys are returned is not specified, even for tables with numeric indexes. To traverse a table in numerical order, use a numerical for or ipairs.

Behavior is undefined if, when using next for traversal, any non-existing key is assigned a value. Assigning a new value (including nil) to an existing field is allowed.

pairs
Returns three values: an iterator function (next or a work-alike), the table, and nil. This is intended for use in the iterator form of :

for k, v in pairs( t ) do    block end

This will iterate over the key-value pairs in  just as next would; see the documentation for next for restrictions on modifying the table during traversal.

The standard behavior may be overridden by providing a __pairs metamethod. If that metamethod exists, the call to pairs will return the three values returned by  instead.

pcall
Calls the function  with the given arguments in protected mode. This means that if an error is raised during the call to, pcall will return false and the error message raised. If no error occurs, pcall will return true and all values returned by the call.

In pseudocode,  might be defined something like this:

function pcall( f, ... ) try return true, f( ... ) catch ( message ) return false, message end end

rawequal
This is equivalent to  except that it ignores any __eq metamethod.

rawget
This is equivalent to  except that it ignores any __index metamethod.

rawset
This is equivalent to  except that it ignores any __newindex metamethod.

select
If  is a number, returns all arguments in   after that index. If  is the string '#', returns the count of arguments in.

In other words,  is something roughly like the following except that it will work correctly even when   contains nil values (see documentation for # and unpack for the problem with nils).

function select( index, ... ) local t = { ... }    if index == '#' then return #t else return unpack( t, index ) end end

setmetatable
Sets the metatable of a table. may be nil, but must be explicitly provided.

If the current metatable has a __metatable field,  will throw an error.

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

The optional  (default 10) specifies the base to interpret the numeral. The base may be any integer between 2 and 36, inclusive. In bases above 10, the letter 'A' (in either upper or lower case) represents 10, 'B' represents 11, and so forth, with 'Z' representing 35.

In base 10, the value may have a decimal part, be expressed in E notation, and may have a leading "0x" to indicate base 16. In other bases, only unsigned integers are accepted.

tostring
Converts  to a string. See Data types above for details on how each type is converted.

The standard behavior for tables may be overridden by providing a __tostring metamethod. If that metamethod exists, the call to tostring will return the single value returned by  instead.

type
Returns the type of  as a string: "nil", "number", "string", "boolean", "table", or "function".

unpack
Returns values from the given table, something like  would do if written out manually. If nil or not given,  defaults to 1 and   defaults to.

Note that results are not deterministic if  is not a sequence and   is nil or unspecified; see Length operator for details.

xpcall
This is much like, except that the error message is passed to the function   before being returned.

In pseudocode,  might be defined something like this:

function xpcall( f, errhandler ) try return true, f catch ( message ) message = errhandler( message ) return false, message end end

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 stack level to start the traceback.

math.abs
Returns the absolute value of.

math.acos
Returns the arc cosine of  (given in radians).

math.asin
Returns the arc sine of  (given in radians).

math.atan
Returns the arc tangent of  (given in radians).

math.atan2
Returns the arc tangent of  (given in radians), using the signs of both parameters to find the quadrant of the result.

math.ceil
Returns the smallest integer larger than or equal to.

math.cos
Returns the cosine of  (given in radians).

math.cosh
Returns the hyperbolic cosine of.

math.deg
Returns the angle  (given in radians) in degrees.

math.exp
Returns the value $$e^x$$.

math.floor
Returns the largest integer smaller than or equal to.

math.fmod
Returns the remainder of the division of  by   that rounds the quotient towards zero.

math.frexp
Returns two values  and   such that:
 * If  is finite and non-zero: $$x = m \times 2^e$$,   is an integer, and the absolute value of   is in the range $$[0.5, 1)$$
 * If  is zero:   and   are 0
 * If  is NaN or infinite:   is   and   is not specified

math.huge
The value representing positive infinity; larger than or equal to any other numerical value.

math.ldexp
Returns $$m \times 2^e$$ ( should be an integer).

math.log
Returns the natural logarithm of.

math.log10
Returns the base-10 logarithm of.

math.max
Returns the maximum value among its arguments.

Behavior with NaNs is not specified. With the current implementation, NaN will be returned if  is NaN, but any other NaNs will be ignored.

math.min
Returns the minimum value among its arguments.

Behavior with NaNs is not specified. With the current implementation, NaN will be returned if  is NaN, but any other NaNs will be ignored.

math.modf
Returns two numbers, the integral part of  and the fractional part of.

math.pi
The value of $$\pi$$.

math.pow
Equivalent to.

math.rad
Returns the angle  (given in degrees) in radians.

math.random
Returns a pseudo-random number.

The arguments  and   may be omitted, but if specified must be convertible to integers.
 * With no arguments, returns a real number in the range $$[0,1)$$
 * With one argument, returns an integer in the range $$[1,m]$$
 * With two arguments, returns an integer in the range $$[m,n]$$

math.randomseed
Sets  as the seed for the pseudo-random generator.

Note that using the same seed will cause  to output the same sequence of numbers.

math.sin
Returns the sine of  (given in radians).

math.sinh
Returns the hyperbolic sine of.

math.sqrt
Returns the square root of. Equivalent to.

math.tan
Returns the tangent of  (given in radians).

math.tanh
Returns the hyperbolic tangent of.

os.clock
Returns an approximation of the amount in seconds of CPU time used by the program.

os.date

 * Language library's formatDate may be used for more comprehensive date formatting

Returns a string or a table containing date and time, formatted according to. If the format is omitted or nil, "%c" is used.

If  is given, it is the time to be formatted (see  ). Otherwise the current time is used.

If  starts with '!', then the date is formatted in UTC rather than the server's local time. After this optional character, if format is the string "*t", then date returns a table with the following fields:
 * year (full)
 * month (1–12)
 * day (1–31)
 * hour (0–23)
 * min (0–59)
 * sec (0–60)
 * wday (weekday, Sunday is 1)
 * yday (day of the year)
 * isdst (daylight saving flag, a boolean; may be absent if the information is not available)

If format is not "*t", then date returns the date as a string, formatted according to the same rules as the C function strftime.

os.difftime
Returns the number of seconds from  to.

os.time
Returns a number representing the current time.

When called without arguments, returns the current time. If passed a table, the time encoded in the table will be parsed. The table must have the fields "year", "month", and "day", and may also include "hour" (default 12), "min" (default 0), "sec" (default 0), and "isdst".

require
Loads the specified module.

First, it looks in  to see if the module is already loaded. If so, returns.

Otherwise, it calls each loader in the  sequence to attempt to find a loader for the module. If a loader is found, that loader is called. The value returned by the loader is stored into  and is returned.

See the documentation for  for information on the loaders available.

Note that every required module is loaded in its own sandboxed environment, so it cannot export global variables as is sometimes done in Lua 5.1. Instead, everything that the module wishes to export should be included in the table returned by the module.

For example, if you have a module "Module:Giving" containing the following: You can load this in another module with code such as this:

package.loaded
This table holds the loaded modules. The keys are the module names, and the values are the values returned when the module was loaded.

package.loaders
This table holds the sequence of searcher functions to use when loading modules. Each searcher function is called with a single argument, the name of the module to load. If the module is found, the searcher must return a function that will actually load the module and return the value to be returned by require. Otherwise, it must return nil.

Scribunto provides two searchers:
 * 1) Look in   for the loader function
 * 2) Look in the modules provided with Scribunto for the module name, and if that fails look in the Module: namespace. The "Module:" prefix must be provided.

Note that the standard Lua loaders are not included.

package.preload
This table holds loader functions, used by the first searcher Scribunto includes in package.loaders.

package.seeall
Sets the __index metamethod for  to _G.

String library
In all string functions, the first character is at position 1, not position 0 as in C, PHP, and JavaScript. Indexes may be negative, in which case they count from the end of the string: position -1 is the last character in the string, -2 is the second-last, and so on.

The string library assumes one-byte character encodings. It cannot handle Unicode characters. To operate on Unicode strings, use the corresponding methods in the Scribunto Ustring library.

string.byte
If the string is considered as an array of bytes, returns the byte values for,  , ···,. The default value for  is 1; the default value for  is. Identical to mw.ustring.byte.

string.char
Receives zero or more integers. Returns a string with length equal to the number of arguments, in which each character has the byte value equal to its corresponding argument. See mw.ustring.char for a similar function that uses Unicode codepoints rather than byte values.

string.find
Looks for the first match of  in the string. If it finds a match, then  returns the offsets in   where this occurrence starts and ends; otherwise, it returns nil. If the pattern has captures, then in a successful match the captured values are also returned after the two indices.

A third, optional numerical argument  specifies where to start the search; its default value is 1 and can be negative. A value of true as a fourth, optional argument  turns off the pattern matching facilities, so the function does a plain "find substring" operation, with no characters in   being considered "magic".

Note that if  is given, then   must be given as well.

See mw.ustring.find for a similar function extended as described in Ustring patterns and where the  offset is in characters rather than bytes.

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 uses a limited subset of the format specifiers:
 * Recognized flags are '-', '+', ' ', '#', and '0'.
 * Integer field widths up to 99 are supported. '*' is not supported.
 * Integer precisions up to 99 are supported. '*' is not supported.
 * Length modifiers are not supported.
 * Recognized conversion specifiers are 'c', 'd', 'i', 'o', 'u', 'x', 'X', 'e', 'E', 'f', 'g', 'G', 's', '%', and the non-standard 'q'.
 * Positional specifiers (e.g. "%2$s") are not supported.

The conversion specifier 'q' is like 's', but formats the 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.

Conversion between strings and numbers is performed as specified in Data types; other types are not automatically converted to strings. Strings containing NUL characters (byte value 0) are not properly handled.

Identical to mw.ustring.format.

string.gmatch
Returns an iterator function that, each time it is called, returns the next captures from  over string. If  specifies no captures, then the whole match is produced in each call.

For this function, a ' ' at the start of a pattern is not magic, as this would prevent the iteration. It is treated as a literal character.

See mw.ustring.gmatch for a similar function for which the pattern is extended as described in Ustring patterns.

string.gsub
Returns a copy of  in which all (or the first , if given) occurrences of the   have been replaced by a replacement string specified by  , which can be a string, a table, or a function. also returns, as its second value, the total number of matches that occurred.

If  is a string, then its value is used for replacement. The character  works as an escape character: any sequence in   of the form  , with n between 1 and 9, stands for the value of the n-th captured substring. The sequence  stands for the whole match, and the sequence   stands for a single.

If  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.

If  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.

If the value returned by the table query or by the function call is a string or a number, then it is used as the replacement string; otherwise, if it is false or nil, then there is no replacement (that is, the original match is kept in the string).

See mw.ustring.gsub for a similar function in which the pattern is extended as described in Ustring patterns.

string.len
Returns the length of the string, in bytes. Is not confused by ASCII NUL characters. Equivalent to.

See mw.ustring.len for a similar function using Unicode codepoints rather than bytes.

string.lower
Returns a copy of this string with all ASCII uppercase letters changed to lowercase. All other characters are left unchanged.

See mw.ustring.lower for a similar function in which all characters with uppercase to lowercase definitions in Unicode are converted.

string.match
Looks for the first match of  in the string. If it finds one, then  returns the captures from the pattern; otherwise it returns nil. If  specifies no captures, then the whole match is returned.

A third, optional numerical argument  specifies where to start the search; its default value is 1 and can be negative.

See mw.ustring.match for a similar function in which the pattern is extended as described in Ustring patterns and the  offset is in characters rather than bytes.

string.rep
Returns a string that is the concatenation of  copies of the string. Identical to mw.ustring.rep.

string.reverse
Returns a string that is the string  reversed (bytewise).

string.sub
Returns the substring of  that starts at   and continues until  ;   and   can be negative. If  is nil or omitted, -1 is used.

In particular, the call  returns a prefix of   with length , and   returns a suffix of   with length.

See mw.ustring.sub for a similar function in which the offsets are characters rather than bytes.

string.upper
Returns a copy of this string with all ASCII lowercase letters changed to uppercase. All other characters are left unchanged.

See mw.ustring.upper for a similar function in which all characters with uppercase to lowercase definitions in Unicode are converted.

Patterns
Note that Lua's patterns are similar to regular expressions, but are not identical. In particular, note the following differences from regular expressions and PCRE:
 * The quoting character is percent, not backslash.
 * Dot always matches all characters, including newlines.
 * No case-insensitive mode.
 * No alternation (the  operator).
 * Quantifiers (, ,  , and  ) may only be applied to individual characters or character classes, not to capture groups.
 * The only non-greedy quantifier is, which is equivalent to PCRE's   quantifier.
 * No generalized finite quantifier (e.g. the  quantifier in PCRE).
 * The only zero-width assertions are,  , and the   "frontier" pattern; assertions such as PCRE's   or   are not present.
 * Patterns themselves do not recognize character escapes such as '\ddd'. However, since patterns are strings these sort of escapes may be used in the string literals used to create the pattern-string.

Also note that a pattern cannot contain embedded zero bytes (ASCII NUL, ). Use  instead.

Also see Ustring patterns for a similar pattern-matching scheme using Unicode characters.

Character class
A character class is used to represent a set of characters. The following combinations are allowed in describing a character class:


 * x: (where x is not one of the magic characters ) represents the character x itself.
 *  : (a dot) represents all characters.
 *  : represents all ASCII letters.
 *  : represents all ASCII control characters.
 *  : represents all digits.
 *  : represents all ASCII lowercase letters.
 *  : represents all punctuation characters.
 *  : represents all ASCII space characters.
 *  : represents all ASCII uppercase letters.
 *  : represents all ASCII alphanumeric characters.
 *  : represents all hexadecimal digits.
 *  : represents ASCII NUL, the zero byte.
 *  : All characters not in.
 *  : All characters not in.
 *  : All characters not in.
 *  : All characters not in.
 *  : All characters not in.
 *  : All characters not in.
 *  : All characters not in.
 *  : All characters not in.
 *  : All characters not in.
 *  : All characters not in.
 *  : (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.
 *  : represents the class which is the union of all characters in set. A range of characters can be specified by separating the end characters of the range with a ' '. All classes  described above can also be used as components in set. All other characters in set represent themselves. For example,   (or  ) represents all alphanumeric characters plus the underscore,   represents the octal digits, and   represents the octal digits plus the lowercase letters plus the ' ' character. The interaction between ranges and classes is not defined. Therefore, patterns like   or   have no meaning.
 *  : represents the complement of set, where set is interpreted as above.

Pattern items
A pattern item can be


 * a single character class, which matches any single character in the class;
 * a single character class followed by ' ', which matches 0 or more repetitions of characters in the class. These repetition items will always match the longest possible sequence;
 * a single character class followed by ' ', which matches 1 or more repetitions of characters in the class. These repetition items will always match the longest possible sequence;
 * a single character class followed by ' ', which also matches 0 or more repetitions of characters in the class. Unlike ' ', these repetition items will always match the shortest possible sequence;
 * a single character class followed by ' ', which matches 0 or 1 occurrence of a character in the class;
 * , for n between 1 and 9; such item matches a substring equal to the n-th captured string (see below);
 * , 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  matches expressions with balanced parentheses.


 * , a frontier pattern; such item matches an empty string at any position such that the next character belongs to set and the previous character does not belong to set. The set set is interpreted as previously described. The beginning and the end of the subject are handled as if they were the character '\0'. Note that frontier patterns were present but undocumented in Lua 5.1, and officially added to Lua in 5.2. The implementation in Lua 5.2.1 is unchanged from that in 5.1.0.

Pattern
A pattern is a sequence of pattern items.

A ' ' 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.

Captures
A pattern can contain sub-patterns enclosed in parentheses; they describe captures. When a match succeeds, the substrings of the subject string that match captures are stored ("captured") for future use. Captures are numbered according to their left parentheses. For instance, in the pattern, the part of the string matching   is stored as the first capture (and therefore has number 1); the character matching   is captured with number 2, and the part matching   has number 3.

Capture references can appear in the pattern string itself, and refer back to text that was captured earlier in the match. For example,  will match any pair of identical lowercase letters, while   will match any 7-letter palindrome.

As a special case, the empty capture  captures the current string position (a number). For instance, if we apply the pattern  on the string , there will be two captures: 3 and 5.

Table library
Most functions in the table library assume that the table represents a sequence.

The functions,  , and   may be available but are deprecated. Use a for loop with pairs, a for loop with ipairs, and the length operator instead.

table.concat
Given an array where all elements are strings or numbers, returns.

The default value for  is the empty string, the default for   is 1, and the default for   is the length of the table. If  is greater than , returns the empty string.

table.insert
Inserts element  at position   in , shifting up other elements to open space, if necessary. The default value for  is the length of the table plus 1, so that a call   inserts   at the end of table.

Elements up to  are shifted; see Length operator for caveats if the table is not a sequence.

table.maxn
Returns the largest positive numerical index of the given table, or zero if the table has no positive numerical indices.

To do this, it iterates over the whole table. This is roughly equivalent to

function table.maxn( table ) local maxn, k = 0, nil repeat k = next( table, k ) if type( k ) == 'number' and k > maxn then maxn = k        end until not k    return maxn end

table.remove
Removes from  the element at position  , shifting down other elements to close the space, if necessary. Returns the value of the removed element. The default value for  is the length of the table, so that a call   removes the last element of table.

Elements up to  are shifted; see Length operator for caveats if the table is not a sequence.

table.sort
Sorts table elements in a given order, in-place, from  to. If  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   will be true after the sort). If  is not given, then the standard Lua operator   is used instead.

The sort algorithm is not stable; that is, elements considered equal by the given order may have their relative positions changed by the sort.

Scribunto libraries
All Scribunto libraries are located in the table.

mw.allToString
Calls tostring on all arguments, then concatenates them with tabs as separators.

mw.clone
Creates a deep copy of a value. All tables (and their metatables) are reconstructed from scratch. Functions are still shared, however.

mw.getCurrentFrame
Returns the current frame object.

mw.incrementExpensiveFunctionCount
Adds one to the "expensive parser function" count, and throws an exception if it exceeds the limit (see $wgExpensiveParserFunctionLimit).

mw.isSubsting
Returns true if the current  is being substed, false otherwise. See Returning text above for discussion on differences when substing versus not substing.

mw.loadData
Sometimes a module needs large tables of data; for example, a general-purpose module to convert units of measure might need a large table of recognized units and their conversion factors. And sometimes these modules will be used many times in one page. Parsing the large data table for every  can use a significant amount of time. To avoid this issue,  is provided.

works like, with the following differences:
 * The loaded module is evaluated only once per page, rather than once per  call.
 * The loaded module is not recorded in.
 * The value returned from the loaded module must be a table. Other data types are not supported.
 * The returned table (and all subtables) may contain only booleans, numbers, strings, and other tables. Other data types, particularly functions, are not allowed.
 * The returned table (and all subtables) may not have a metatable.
 * All table keys must be booleans, numbers, or strings.
 * The table actually returned by  has metamethods that provide read-only access to the table returned by the module. Since it does not contain the data directly,   and   will work but other methods, including ,  , and the functions in the Table library, will not work correctly.

The hypothetical unit-conversion module mentioned above might store its code in "Module:Convert" and its data in "Module:Convert/data", and "Module:Convert" would use  to efficiently load the data.

mw.dumpObject
Serializes  to a human-readable representation, then returns the resulting string.

mw.log
Passes the arguments to mw.allToString, then appends the resulting string to the log buffer.

In the debug console, the function  is an alias for this function.

mw.logObject
Calls mw.dumpObject and appends the resulting string to the log buffer. If  is given, it will be added to the log buffer followed by an equals sign before the serialized string is appended (i.e. the logged text will be "prefix = object-string").

Frame object
The frame object is the interface to the parameters passed to, and to the parser.

frame.args
A table for accessing the arguments passed to the frame. For example, if a module is called from wikitext with

then  will return "arg1",   will return "arg2", and   (or  ) will return "arg3". It is also possible to iterate over arguments using  or.

Note that values in this table are always strings;  may be used to convert them to numbers, if necessary. Keys, however, are numbers even if explicitly supplied in the invocation: gives string values "1" and "2" indexed by numeric keys 1 and 2.

As in MediaWiki template invocations, named arguments will have leading and trailing whitespace removed from both the name and the value before they are passed to Lua, whereas unnamed arguments will not have whitespace stripped.

For performance reasons, frame.args uses a metatable, rather than directly containing the arguments. Argument values are requested from MediaWiki on demand. This means that most other table methods will not work correctly, including,  , and the functions in the Table library.

If preprocessor syntax such as template invocations and triple-brace arguments are included within an argument to #invoke, they will be expanded before being passed to Lua. If certain special tags written in XML notation, such as,  ,   and  , are included as arguments to #invoke, then these tags will be converted to "strip markers" — special strings which begin with a delete character (ASCII 127), to be replaced with HTML after they are returned from #invoke.

frame:callParserFunction

 * Note the use of named arguments.

Call a parser function, returning an appropriate string. Whenever possible, native Lua functions or Scribunto library functions should be preferred to this interface.

The following calls are approximately equivalent to the indicated wikitext:

--      frame:callParserFunction{ name = 'ns', args = 0 } --  frame:callParserFunction{ name = '#tag', args = { 'nowiki', 'some text' } } frame:callParserFunction( '#tag', { 'nowiki', 'some text' } ) frame:callParserFunction( '#tag', 'nowiki', 'some text' ) frame:callParserFunction( '#tag:nowiki', 'some text' ) --  frame:callParserFunction{ name = '#tag:ref', args = { 'some text', name = 'foo', group = 'bar' } }

Note that, as with frame:expandTemplate, the function name and arguments are not preprocessed before being passed to the parser function.

frame:expandTemplate

 * Note the use of named arguments.

This is transclusion. The call

frame:expandTemplate{ title = 'template', args = { 'arg1', 'arg2', name = 'arg3' } }

does roughly the same thing from Lua that  does in wikitext. As in transclusion, if the passed title does not contain a namespace prefix it will be assumed to be in the Template: namespace.

Note that the title and arguments are not preprocessed before being passed into the template:

-- This is roughly equivalent to wikitext like --  frame:expandTemplate{ title = 'template', args = { '|' } } -- This is roughly equivalent to wikitext like --  frame:expandTemplate{ title = 'template', args = { ' | ' } }

frame:extensionTag
This is equivalent to a call to frame:callParserFunction with function name  and with   prepended to.

-- These are equivalent frame:extensionTag{ name = 'ref', content = 'some text', args = { name = 'foo', group = 'bar' } } frame:extensionTag( 'ref', 'some text', { name = 'foo', group = 'bar' } ) frame:callParserFunction{ name = '#tag:ref', args = { 'some text', name = 'foo', group = 'bar' } }

frame:getParent
Called on the frame created by, returns the frame for the page that called. Called on that frame, returns nil.

frame:getTitle
Returns the title associated with the frame as a string. For the frame created by, this is the title of the module invoked.

frame:newChild

 * Note the use of named arguments.

Create a new Frame object that is a child of the current frame, with optional arguments and title.

This is mainly intended for use in the debug console for testing functions that would normally be called by. The number of frames that may be created at any one time is limited.

frame:preprocess
This expands wikitext in the context of the frame, i.e. templates, parser functions, and parameters such as  are expanded. Certain special tags written in XML-style notation, such as,  ,   and  , will be replaced with "strip markers" &mdash; special strings which begin with a delete character (ASCII 127), to be replaced with HTML after they are returned from.

If you are expanding a single template, use  instead of trying to construct a wikitext string to pass to this method. It's faster and less prone to error if the arguments contain pipe characters or other wikimarkup.

frame:getArgument
Gets an object for the specified argument, or nil if the argument is not provided.

The returned object has one method,, that returns the expanded wikitext for the argument.

frame:newParserValue
Returns an object with one method,, that returns the result of.

frame:newTemplateParserValue

 * Note the use of named arguments.

Returns an object with one method,, that returns the result of   called with the given arguments.

frame:argumentPairs
Same as. Included for backwards compatibility.

HTML library
is a fluent interface for building complex HTML from Lua. A mw.html object can be created using.

Functions documented as  are available on the global   table; functions documented as   are methods of an mw.html object (see  ).

A basic example could look like this:

mw.html.create
Creates a new mw.html object containing a  html element. You can also pass an empty string or nil as  in order to create an empty mw.html object.

can be a table with the following keys:
 * : Force the current tag to be self-closing, even if mw.html doesn't recognize it as self-closing
 * : Parent of the current mw.html instance (intended for internal usage)

mw.html:node
Appends a child mw.html node to the current mw.html instance. If a nil parameter is passed, this is a no-op.

mw.html:wikitext
Appends an undetermined number of wikitext strings to the mw.html object.

mw.html:newline
Appends a newline to the mw.html object.

mw.html:tag
Appends a new child node with the given  to the builder, and returns a mw.html instance representing that new node. The  parameter is identical to that of

mw.html:attr
Set an HTML attribute with the given  and   on the node. Alternatively a table holding name->value pairs of attributes to set can be passed. In the first form, a value of nil causes any attribute with the given name to be unset if it was previously set.

mw.html:getAttr
Get the value of a html attribute previously set using  with the given.

mw.html:addClass
Adds a class name to the node's class attribute. If a nil parameter is passed, this is a no-op.

mw.html:css
Set a CSS property with the given  and   on the node. Alternatively a table holding name->value pairs of properties to set can be passed. In the first form, a value of nil causes any property with the given name to be unset if it was previously set.

mw.html:cssText
Add some raw  to the node's style attribute. If a nil parameter is passed, this is a no-op.

mw.html:done
Returns the parent node under which the current node was created. Like jQuery.end, this is a convenience function to allow the construction of several child nodes to be chained together into a single statement.

mw.html:allDone
Like, but traverses all the way to the root node of the tree and returns it.

Language library
Language codes are described at Language code. Many of MediaWiki's language codes are similar to IETF language tags, but not all MediaWiki language codes are valid IETF tags or vice versa.

Functions documented as  are available on the global   table; functions documented as   are methods of a language object (see  ).

mw.language.fetchLanguageName
The full name of the language for the given language code: native name (language autonym) by default, name translated in target language if a value is given for.

mw.language.fetchLanguageNames
Fetch the list of languages known to MediaWiki, returning a table mapping language code to language name.

By default the name returned is the language autonym; passing a language code for  returns all names in that language.

By default, only language names known to MediaWiki are returned; passing  for   will return all available languages (e.g. from Extension:CLDR), while passing   will include only languages having customized messages included with MediaWiki core or enabled extensions. To explicitly select the default,  may be passed.

mw.language.getContentLanguage
Returns a new language object for the wiki's default content language.

mw.language.getFallbacksFor
Returns a list of MediaWiki's fallback language codes for the specified code.

mw.language.isKnownLanguageTag
Returns true if a language code is known to MediaWiki.

A language code is "known" if it is a "valid built-in code" (i.e. it returns true for ) and returns a non-empty string for.

mw.language.isSupportedLanguage
Checks whether any localisation is available for that language code in MediaWiki.

A language code is "supported" if it is a "valid" code (returns true for ), contains no uppercase letters, and has a message file in the currently-running version of MediaWiki.

It is possible for a language code to be "supported" but not "known" (i.e. returning true for ). Also note that certain codes are "supported" despite  returning false.

mw.language.isValidBuiltInCode
Returns true if a language code is of a valid form for the purposes of internal customisation of MediaWiki.

The code may not actually correspond to any known language.

A language code is a "valid built-in code" if it is a "valid" code (i.e. it returns true for ); consists of only ASCII letters, numbers, and hyphens; and is at least two characters long.

Note that some codes are "supported" (i.e. returning true from ) even though this function returns false.

mw.language.isValidCode
Returns true if a language code string is of a valid form, whether or not it exists. This includes codes which are used solely for customisation via the MediaWiki namespace.

The code may not actually correspond to any known language.

A language code is valid if it does not contain certain unsafe characters (colons, single- or double-quotes, slashs, backslashs, angle brackets, ampersands, or ASCII NULs) and is otherwise allowed in a page title.

mw.language.new
Creates a new language object. Language objects do not have any publicly accessible properties, but they do have several methods, which are documented below.

mw.language:getCode
Returns the language code for this language object.

mw.language:getFallbackLanguages
Returns a list of MediaWiki's fallback language codes for this language object. Equivalent to.

mw.language:isRTL
Returns true if the language is written right-to-left, false if it is written left-to-right.

mw.language:lc
Converts the string to lowercase, honoring any special rules for the given language.

When the Ustring library is loaded, the mw.ustring.lower function is implemented as a call to.

mw.language:lcfirst
Converts the first character of the string to lowercase, as with lang:lc.

mw.language:uc
Converts the string to uppercase, honoring any special rules for the given language.

When the Ustring library is loaded, the mw.ustring.upper function is implemented as a call to.

mw.language:ucfirst
Converts the first character of the string to uppercase, as with lang:uc.

mw.language:caseFold
Converts the string to a representation appropriate for case-insensitive comparison. Note that the result may not make any sense when displayed.

mw.language:formatNum
Formats a number with grouping and decimal separators appropriate for the given language. Given 123456.78, this may produce "123,456.78", "123.456,78", or even something like "١٢٣٬٤٥٦٫٧٨" depending on the language and wiki configuration.

mw.language:formatDate
Formats a date according to the given format string. If  is omitted, the default is the current time. The value for  must be a boolean or nil; if true, the time is formatted in the wiki's local time rather than in UTC.

The format string and supported values for  are identical to those for the #time parser function from Extension:ParserFunctions. Note that backslashes may need to be doubled in the Lua string where they wouldn't in wikitext:

-- This outputs a newline, where would output a literal "n" lang:formatDate( '\n' ) -- This outputs a literal "n", where would output a backslash -- followed by the month number. lang:formatDate( '\\n' ) -- This outputs a backslash followed by the month number, where -- would output two backslashes followed by the month number. lang:formatDate( '\\\\n' )

mw.language:formatDuration
Breaks a duration in seconds into more human-readable units, e.g. 12345 to 3 hours, 25 minutes and 45 seconds, returning the result as a string.

, if given, is a table with values naming the interval units to use in the response. These include 'millennia', 'centuries', 'decades', 'years', 'weeks', 'days', 'hours', 'minutes', and 'seconds'.

mw.language:parseFormattedNumber
This takes a number as formatted by lang:formatNum and returns the actual number. In other words, this is basically a language-aware version of.

mw.language:convertPlural
This chooses the appropriate grammatical form from  (which must be a sequence table) or   based on the number. For example, in English you might use  or   to generate grammatically-correct text whether there is only 1 sock or 200 socks.

The necessary values for the sequence are language-dependent, see Help:Magic words and FAQ for some details.

mw.language:convertGrammar

 * Note the different parameter order between the two aliases.  matches the order of the method of the same name on MediaWiki's Language object, while   matches the order of the parser function of the same name, documented at Help:Magic words.

This chooses the appropriate inflected form of  for the given inflection code.

The possible values for  and   are language-dependent, see Help:Magic words and Grammar for some details.

mw.language:gender
Chooses the string corresponding to the gender of, which may be "male", "female", or a registered user name.

mw.language:getArrow
Returns a Unicode arrow character corresponding to :
 * forwards: Either "→" or "←" depending on the directionality of the language.
 * backwards: Either "←" or "→" depending on the directionality of the language.
 * left: "←"
 * right: "→"
 * up: "↑"
 * down: "↓"

mw.language:getDir
Returns "ltr" or "rtl", depending on the directionality of the language.

mw.language:getDirMark
Returns a string containing either U+200E (the left-to-right mark) or U+200F (the right-to-left mark), depending on the directionality of the language and whether  is a true or false value.

mw.language:getDirMarkEntity
Returns "&amp;lrm;" or "&amp;rlm;", depending on the directionality of the language and whether  is a true or false value.

mw.language:getDurationIntervals
Breaks a duration in seconds into more human-readable units, e.g. 12345 to 3 hours, 25 minutes and 45 seconds, returning the result as a table mapping unit names to numbers.

, if given, is a table with values naming the interval units to use in the response. These include 'millennia', 'centuries', 'decades', 'years', 'days', 'hours', 'minutes', and 'seconds'.

Message library
This library is an interface to the localisation messages and the MediaWiki: namespace.

Functions documented as  are available on the global   table; functions documented as   are methods of a message object (see  ).

mw.message.new
Creates a new message object for the given message.

The message object has no properties, but has several methods documented below.

mw.message.newFallbackSequence
Creates a new message object for the given messages (the first one that exists will be used).

The message object has no properties, but has several methods documented below.

mw.message.newRawMessage
Creates a new message object, using the given text directly rather than looking up an internationalized message. The remaining parameters are passed to the new object's  method.

The message object has no properties, but has several methods documented below.

mw.message.rawParam
Wraps the value so that it will not be parsed as wikitext by.

mw.message.numParam
Wraps the value so that it will automatically be formatted as by. Note this does not depend on the Language library actually being available.

mw.message.getDefaultLanguage
Returns a Language object for the default language.

mw.message:params
Add parameters to the message, which may be passed as individual arguments or as a sequence table. Parameters must be numbers, strings, or the special values returned by mw.message.numParam or mw.message.rawParam. If a sequence table is used, parameters must be directly present in the table; references using the __index metamethod will not work.

Returns the  object, to allow for call chaining.

mw.message:rawParams
Like params, but has the effect of passing all the parameters through mw.message.rawParam first.

Returns the  object, to allow for call chaining.

mw.message:numParams
Like params, but has the effect of passing all the parameters through mw.message.numParam first.

Returns the  object, to allow for call chaining.

mw.message:inLanguage
Specifies the language to use when processing the message. may be a string or a table with a  method (i.e. a Language object).

The default language is the one returned by.

Returns the  object, to allow for call chaining.

mw.message:useDatabase
Specifies whether to look up messages in the MediaWiki: namespace (i.e. look in the database), or just use the default messages distributed with MediaWiki.

The default is true.

Returns the  object, to allow for call chaining.

mw.message:plain
Substitutes the parameters and returns the message wikitext as-is. Template calls and parser functions are intact.

mw.message:exists
Returns a boolean indicating whether the message key exists.

mw.message:isBlank
Returns a boolean indicating whether the message key has content. Returns true if the message key does not exist or the message is the empty string.

mw.message:isDisabled
Returns a boolean indicating whether the message key is disabled. Returns true if the message key does not exist or if the message is the empty string or the string "-".

mw.site.currentVersion
A string holding the current version of MediaWiki.

mw.site.scriptPath
The value of $wgScriptPath.

mw.site.server
The value of $wgServer.

mw.site.siteName
The value of $wgSitename.

mw.site.stylePath
The value of $wgStylePath.

mw.site.namespaces
Table holding data for all namespaces, indexed by number.

The data available is:
 * id: Namespace number.
 * name: Local namespace name.
 * canonicalName: Canonical namespace name.
 * displayName: Set on namespace 0, the name to be used for display (since the name is often the empty string).
 * hasSubpages: Whether subpages are enabled for the namespace.
 * hasGenderDistinction: Whether the namespace has different aliases for different genders.
 * isCapitalized: Whether the first letter of pages in the namespace is capitalized.
 * isContent: Whether this is a content namespace.
 * isIncludable: Whether pages in the namespace can be transcluded.
 * isMovable: Whether pages in the namespace can be moved.
 * isSubject: Whether this is a subject namespace.
 * isTalk: Whether this is a talk namespace.
 * defaultContentModel: The default content model for the namespace, as a string.
 * aliases: List of aliases for the namespace.
 * subject: Reference to the corresponding subject namespace's data.
 * talk: Reference to the corresponding talk namespace's data.
 * associated: Reference to the associated namespace's data.

A metatable is also set that allows for looking up namespaces by name (localized or canonical). For example, both  and   will return information about the Project namespace.

mw.site.contentNamespaces
Table holding just the content namespaces, indexed by number. See mw.site.namespaces for details.

mw.site.subjectNamespaces
Table holding just the subject namespaces, indexed by number. See mw.site.namespaces for details.

mw.site.talkNamespaces
Table holding just the talk namespaces, indexed by number. See mw.site.namespaces for details.

mw.site.stats
Table holding site statistics. Available statistics are:


 * pages: Number of pages in the wiki.
 * articles: Number of articles in the wiki.
 * files: Number of files in the wiki.
 * edits: Number of edits in the wiki.
 * views: Number of views in the wiki. Not available if $wgDisableCounters is set.
 * users: Number of users in the wiki.
 * activeUsers: Number of active users in the wiki.
 * admins: Number of users in group 'sysop' in the wiki.

mw.site.stats.pagesInCategory


Gets statistics about the category. If  is unspecified, nil, or "*", returns a table with the following properties:
 * all: Total pages, files, and subcategories.
 * subcats: Number of subcategories.
 * files: Number of files.
 * pages: Number of pages.

If  is one of the above keys, just the corresponding value is returned instead.

Each new category queried will increment the expensive function count.

mw.site.stats.pagesInNamespace
Returns the number of pages in the given namespace (specify by number).

mw.site.stats.usersInGroup
Returns the number of users in the given group.

mw.site.interwikiMap
Returns a table holding data about available interwiki prefixes. If  is the string "local", then only data for local interwiki prefixes is returned. If  is the string "!local", then only data for non-local prefixes is returned. If no filter is specified, data for all prefixes is returned. A "local" prefix in this context is one that is for the same project. For example, on the English Wikipedia, other-language Wikipedias are considered local, while Wiktionary and such are not.

Keys in the table returned by this function are interwiki prefixes, and the values are subtables with the following properties:
 * prefix - the interwiki prefix.
 * url - the URL that the interwiki points to. The page name is represented by the parameter $1.
 * isProtocolRelative - a boolean showing whether the URL is protocol-relative.
 * isLocal - whether the URL is for a site in the current project.
 * isCurrentWiki - whether the URL is for the current wiki.
 * isTranscludable - whether pages using this interwiki prefix are transcludable. This requires scary transclusion, which is disabled on Wikimedia wikis.
 * isExtraLanguageLink - whether the interwiki is listed in $wgExtraInterlanguageLinkPrefixes.
 * displayText - for links listed in $wgExtraInterlanguageLinkPrefixes, this is the display text shown for the interlanguage link. Nil if not specified.
 * tooltip - for links listed in $wgExtraInterlanguageLinkPrefixes, this is the tooltip text shown when users hover over the interlanguage link. Nil if not specified.

Text library
The text library provides some common text processing functions missing from the String library and the Ustring library. These functions are safe for use with UTF-8 strings.

mw.text.decode
Replaces HTML entities in the string with the corresponding characters.

If  is omitted or false, the only named entities recognized are '&amp;lt;', '&amp;gt;', '&amp;amp;', '&amp;quot;', and '&amp;nbsp;'. Otherwise, the list of HTML5 named entities to recognize is loaded from PHP's function.

mw.text.encode
Replaces characters in a string with HTML entities. Characters '<', '>', '&', '"', and the non-breaking space are replaced with the appropriate named entities; all others are replaced with numeric entities.

If  is supplied, it should be a string as appropriate to go inside brackets in a Ustring pattern, i.e. the "set" in. The default charset is  (the space at the end is the non-breaking space, U+00A0).

mw.text.jsonDecode
Decodes a JSON string. is 0 or a combination (use ) of the flags   and.

Normally JSON's zero-based arrays are renumbered to Lua one-based sequence tables; to prevent this, pass.

To relax certain requirements in JSON, such as no terminal comma in arrays or objects, pass. This is not recommended.

Limitations:
 * Decoded JSON arrays may not be Lua sequences if the array contains null values.
 * JSON objects will drop keys having null values.
 * It is not possible to directly tell whether the input was a JSON array or a JSON object with sequential integer keys.
 * A JSON object having sequential integer keys beginning with 1 will decode to the same table structure as a JSON array with the same values, despite these not being at all equivalent, unless  is used.

mw.text.jsonEncode
Encode a JSON string. Errors are raised if the passed value cannot be encoded in JSON. is 0 or a combination (use ) of the flags   and.

Normally Lua one-based sequence tables are encoded as JSON zero-based arrays; when  is set in , zero-based sequence tables are encoded as JSON arrays.

Limitations:
 * Empty tables are always encoded as empty arrays, not empty objects.
 * Sequence tables cannot be encoded as JSON objects without adding a "dummy" element.
 * To produce objects or arrays with nil values, a tricky implementation of the  metamethod is required.
 * A Lua table having sequential integer keys beginning with 0 will encode as a JSON array, the same as a Lua table having integer keys beginning with 1, unless  is used.
 * When both a number and the string representation of that number are used as keys in the same table, behavior is unspecified.

mw.text.killMarkers
Removes all MediaWiki strip markers from a string.

mw.text.listToText
Join a list, prose-style. In other words, it's like  but with a different separator before the final item.

The default separator is taken from MediaWiki:comma-separator in the wiki's content language, and the default conjuction is MediaWiki:and concatenated with MediaWiki:word-separator.

Examples, using the default values for the messages:

-- Returns the empty string mw.text.listToText( {} ) -- Returns "1" mw.text.listToText( { 1 } ) -- Returns "1 and 2" mw.text.listToText( { 1, 2 } ) -- Returns "1, 2, 3, 4 and 5" mw.text.listToText( { 1, 2, 3, 4, 5 } ) -- Returns "1; 2; 3; 4 or 5" mw.text.listToText( { 1, 2, 3, 4, 5 }, '; ', ' or ' )

mw.text.nowiki
Replaces various characters in the string with HTML entities to prevent their interpretation as wikitext. This includes:
 * The following characters: '"', '&', "'", '<', '=', '>', '[', ']', '{', '|', '}'
 * The following characters at the start of the string or immediately after a newline: '#', '*', ':', ';', space, tab ('\t')
 * Blank lines will have one of the associated newline or carriage return characters escaped
 * "" at the start of the string or immediately after a newline will have the first '-' escaped
 * "__" will have one underscore escaped
 * "://" will have the colon escaped
 * A whitespace character following "ISBN", "RFC", or "PMID" will be escaped

mw.text.split
Splits the string into substrings at boundaries matching the Ustring pattern. If  is specified and true,   will be interpreted as a literal string rather than as a Lua pattern (just as with the parameter of the same name for  ). Returns a table containing the substrings.

For example,  would return a table.

If  matches the empty string,   will be split into individual characters.

mw.text.gsplit
Returns an iterator function that will iterate over the substrings that would be returned by the equivalent call to.

mw.text.tag

 * Note the use of named arguments.

Generates an HTML-style tag for.

If  is given, it must be a table with string keys. String and number values are used as the value of the attribute; boolean true results in the key being output as an HTML5 valueless parameter; boolean false skips the key entirely; and anything else is an error.

If  is not given (or is nil), only the opening tag is returned. If  is boolean false, a self-closed tag is returned. Otherwise it must be a string or number, in which case that content is enclosed in the constructed opening and closing tag. Note the content is not automatically HTML-encoded; use mw.text.encode if needed.

For properly returning extension tags such as, use frame:extensionTag instead.

mw.text.trim
Remove whitespace or other characters from the beginning and end of a string.

If  is supplied, it should be a string as appropriate to go inside brackets in a Ustring pattern, i.e. the "set" in. The default charset is ASCII whitespace,.

mw.text.truncate
Truncates  to the specified length, adding   if truncation was performed. If length is positive, the end of the string will be truncated; if negative, the beginning will be removed. If  is given and true, the resulting string including ellipsis will not be longer than the specified length.

The default value for  is taken from MediaWiki:ellipsis in the wiki's content language.

Examples, using the default "..." ellipsis:

-- Returns "foobarbaz" mw.text.truncate( "foobarbaz", 9 ) -- Returns "fooba..." mw.text.truncate( "foobarbaz", 5 ) -- Returns "...arbaz" mw.text.truncate( "foobarbaz", -5 ) -- Returns "foo..." mw.text.truncate( "foobarbaz", 6, nil, true ) -- Returns "foobarbaz", because that's shorter than "foobarba..." mw.text.truncate( "foobarbaz", 8 )

mw.text.unstripNoWiki
Replaces MediaWiki &lt;nowiki&gt; strip markers with the corresponding text. Other types of strip markers are not changed.

mw.text.unstrip
Equivalent to.

This no longer reveals the HTML behind special page transclusion, &lt;ref&gt; tags, and so on as it did in earlier versions of Scribunto.

mw.title.equals
Test for whether two titles are equal. Note that fragments are ignored in the comparison.

mw.title.compare
Returns -1, 0, or 1 to indicate whether the title  is less than, equal to, or greater than title

mw.title.getCurrentTitle
Returns the title object for the current page.

mw.title.new


Creates a new title object.

If a number  is given, an object is created for the title with that page_id. The title referenced will be counted as linked from the current page. If the page_id does not exist, returns nil. The expensive function count will be incremented if the title object created is not for a title that has already been loaded.

If a string  is given instead, an object is created for that title (even if the page does not exist). If the text string does not specify a namespace,  (which may be any key found in  ) will be used. If the text is not a valid title, nil is returned.

mw.title.makeTitle
Creates a title object with title  in namespace , optionally with the specified   and   prefix. may be any key found in. If the resulting title is not valid, returns nil.

Note that  will create an object for the page Module:Foo, while   will create an object for the page Template:Module:Foo.

Title objects
A title object has a number of properties and methods. Most of the properties are read-only.

Note that fields ending with  return titles as string values whereas the fields ending with   return title objects.


 * id: The page_id. 0 if the page does not exist., and the page will be recorded as a link.
 * interwiki: The interwiki prefix, or the empty string if none.
 * namespace: The namespace number.
 * fragment: The fragment, or the empty string. May be assigned.
 * nsText: The text of the namespace for the page.
 * subjectNsText: The text of the subject namespace for the page.
 * text: The title of the page, without the namespace or interwiki prefixes.
 * prefixedText: The title of the page, with the namespace and interwiki prefixes.
 * fullText: The title of the page, with the namespace and interwiki prefixes and the fragment.
 * rootText: If this is a subpage, the title of the root page without prefixes. Otherwise, the same as.
 * baseText: If this is a subpage, the title of the page it is a subpage of without prefixes. Otherwise, the same as.
 * subpageText: If this is a subpage, just the subpage name. Otherwise, the same as.
 * canTalk: Whether the page for this title could have a talk page.
 * exists: Whether the page exists. Alias for file.exists for Media-namespace titles. For File-namespace titles this checks the existence of the file description page, not the file itself., and the page will be recorded as a link.
 * file, fileExists: See below.
 * isContentPage: Whether this title is in a content namespace.
 * isExternal: Whether this title has an interwiki prefix.
 * isLocal: Whether this title is in this project. For example, on the English Wikipedia, any other Wikipedia is considered "local" while Wiktionary and such are not.
 * isRedirect: Whether this is the title for a page that is a redirect., and the page will be recorded as a link.
 * isSpecialPage: Whether this is the title for a possible special page (i.e. a page in the Special: namespace).
 * isSubpage: Whether this title is a subpage of some other title.
 * isTalkPage: Whether this is a title for a talk page.
 * isSubpageOf( title2 ): Whether this title is a subpage of the given title.
 * inNamespace( ns ): Whether this title is in the given namespace. Namespaces may be specified by anything that is a key found in.
 * inNamespaces( ... ): Whether this title is in any of the given namespaces. Namespaces may be specified by anything that is a key found in.
 * hasSubjectNamespace( ns ): Whether this title's subject namespace is in the given namespace. Namespaces may be specified by anything that is a key found in.
 * contentModel: The content model for this title, as a string., and the page will be recorded as a link.
 * basePageTitle: The same as.
 * rootPageTitle: The same as.
 * talkPageTitle: The same as, or nil if this title cannot have a talk page.
 * subjectPageTitle: The same as.
 * protectionLevels: The page's protection levels. This is a table with keys corresponding to each action (e.g., "edit" and "move"). The table values are arrays, the first item of which is a string containing the protection level. If the page is unprotected, either the table values or the array items will be nil..
 * subPageTitle( text ): The same as.
 * partialUrl: Returns  encoded as it would be in a URL.
 * fullUrl( query, proto ): Returns the full URL (with optional query table/string) for this title.  may be specified to control the scheme of the resulting url: "http", "https", "relative" (the default), or "canonical".
 * localUrl( query ): Returns the local URL (with optional query table/string) for this title.
 * canonicalUrl( query ): Returns the canonical URL (with optional query table/string) for this title.
 * getContent: Returns the (unparsed) content of the page, or nil if there is no page. The page will be recorded as a transclusion.

Title objects may be compared using Relational operators. will return.

File metadata
Title objects representing a page in the File or Media namespace will have a property called. This is a table, structured as follows:
 * exists: Whether the file exists. It will be recorded as an image usage. The  property on a Title object exists for backwards compatibility reasons and is an alias for this property. If this is false, all other file properties will be nil.
 * width: The width of the file. If the file contains multiple pages, this is the width of the first page.
 * height: The height of the file. If the file contains multiple pages, this is the height of the first page.
 * pages: If the file format supports multiple pages, this is a table containing tables for each page of the file; otherwise, it is nil. The # operator can be used to get the number of pages in the file. Each individual page table contains a width and height property.
 * size: The size of the file in bytes.
 * mimeType: The MIME type of the file.

Expensive properties
The properties id, isRedirect, exists, and contentModel require fetching data about the title from the database. For this reason, the expensive function count is incremented the first time one of them is accessed for a page other than the current page. Subsequent accesses of any of these properties for that page will not increment the expensive function count again.

Other properties marked as expensive will always increment the expensive function count the first time they are accessed for a page other than the current page.

mw.uri.encode
Percent-encodes the string. The default type, "QUERY", encodes spaces using '+' for use in query strings; "PATH" encodes spaces as %20; and "WIKI" encodes spaces as '_'.

Note that the "WIKI" format is not entirely reversible, as both spaces and underscores are encoded as '_'.

mw.uri.decode
Percent-decodes the string. The default type, "QUERY", decodes '+' to space; "PATH" does not perform any extra decoding; and "WIKI" decodes '_' to space.

mw.uri.anchorEncode
Encodes a string for use in a MediaWiki URI fragment.

mw.uri.buildQueryString
Encodes a table as a URI query string. Keys should be strings; values may be strings or numbers, sequence tables, or boolean false.

mw.uri.parseQueryString
Decodes a query string to a table. Keys in the string without values will have a value of false; keys repeated multiple times will have sequence tables as values; and others will have strings as values.

mw.uri.canonicalUrl
Returns a URI object for the canonical URL for a page, with optional query string/table.

mw.uri.fullUrl
Returns a URI object for the full URL for a page, with optional query string/table.

mw.uri.localUrl
Returns a URI object for the local URL for a page, with optional query string/table.

mw.uri.new
Constructs a new URI object for the passed string or table. See the description of URI objects for the possible fields for the table.

mw.uri.validate
Validates the passed table (or URI object). Returns a boolean indicating whether the table was valid, and on failure a string explaining what problems were found.

URI object
The URI object has the following fields, some or all of which may be nil:


 * protocol: String protocol/scheme
 * user: String user
 * password: String password
 * host: String host name
 * port: Integer port
 * path: String path
 * query: A table, as from mw.uri.parseQueryString
 * fragment: String fragment.

The following properties are also available:
 * userInfo: String user and password
 * hostPort: String host and port
 * authority: String user, password, host, and port
 * queryString: String version of the query table
 * relativePath: String path, query string, and fragment

will give the URI string.

Methods of the URI object are:

mw.uri:parse
Parses a string into the current URI object. Any fields specified in the string will be replaced in the current object; fields not specified will keep their old values.

mw.uri:clone
Makes a copy of the URI object.

mw.uri:extend
Merges the parameters table into the object's query table.

Ustring library
The ustring library is intended to be a direct reimplementation of the standard String library, except that the methods operate on characters in UTF-8 encoded strings rather than bytes.

Most functions will raise an error if the string is not valid UTF-8; exceptions are noted.

mw.ustring.maxPatternLength
The maximum allowed length of a pattern, in bytes.

mw.ustring.maxStringLength
The maximum allowed length of a string, in bytes.

mw.ustring.byte
Returns individual bytes; identical to string.byte.

mw.ustring.byteoffset
Returns the byte offset of a character in the string. The default for both  and   is 1. may be negative, in which case it counts from the end of the string.

The character at  == 1 is the first character starting at or after byte  ; the character at   == 0 is the first character starting at or before byte. Note this may be the same character. Greater or lesser values of  are calculated relative to these.

mw.ustring.char
Much like string.char, except that the integers are Unicode codepoints rather than byte values.

mw.ustring.codepoint
Much like string.byte, except that the return values are codepoints and the offsets are characters rather than bytes.

mw.ustring.find
Much like string.find, except that the pattern is extended as described in Ustring patterns and the  offset is in characters rather than bytes.

mw.ustring.format
Identical to string.format. Widths and precisions for strings are expressed in bytes, not codepoints.

mw.ustring.gcodepoint
Returns three values for iterating over the codepoints in the string. defaults to 1, and  to -1. This is intended for use in the iterator form of :

mw.ustring.gmatch
Much like string.gmatch, except that the pattern is extended as described in Ustring patterns.

mw.ustring.gsub
Much like string.gsub, except that the pattern is extended as described in Ustring patterns.

mw.ustring.isutf8
Returns true if the string is valid UTF-8, false if not.

mw.ustring.len
Returns the length of the string in codepoints, or nil if the string is not valid UTF-8.

See string.len for a similar function that uses byte length rather than codepoints.

mw.ustring.lower
Much like string.lower, except that all characters with lowercase to uppercase definitions in Unicode are converted.

If the Language library is also loaded, this will instead call lc on the default language object.

mw.ustring.match
Much like string.match, except that the pattern is extended as described in Ustring patterns and the  offset is in characters rather than bytes.

mw.ustring.rep
Identical to string.rep.

mw.ustring.sub
Much like string.sub, except that the offsets are characters rather than bytes.

mw.ustring.toNFC
Converts the string to Normalization Form C. Returns nil if the string is not valid UTF-8.

mw.ustring.toNFD
Converts the string to Normalization Form D. Returns nil if the string is not valid UTF-8.

mw.ustring.upper
Much like string.upper, except that all characters with uppercase to lowercase definitions in Unicode are converted.

If the Language library is also loaded, this will instead call uc on the default language object.

Ustring patterns
Patterns in the ustring functions use the same syntax as the String library patterns. The major difference is that the character classes are redefined in terms of Unicode character properties:
 *  : represents all characters with General Category "Letter".
 *  : represents all characters with General Category "Control".
 *  : represents all characters with General Category "Decimal Number".
 *  : represents all characters with General Category "Lowercase Letter".
 *  : represents all characters with General Category "Punctuation".
 *  : represents all characters with General Category "Separator", plus tab, linefeed, carriage return, vertical tab, and form feed.
 *  : represents all characters with General Category "Uppercase Letter".
 *  : represents all characters with General Category "Letter" or "Decimal Number".
 *  : adds fullwidth character versions of the hex digits.

In all cases, characters are interpreted as Unicode characters instead of bytes, so ranges such as, patterns such as  , and quantifiers applied to multibyte characters will work correctly. Empty captures will capture the position in code points rather than bytes.

Loadable libraries
These libraries are not included by default, but if needed may be loaded using.

bit32
This emulation of the Lua 5.2  library may be loaded using

bit32 = require( 'bit32' )

The bit32 library provides bitwise operations on unsigned 32-bit integers. Input numbers are truncated to integers (in an unspecified manner) and reduced modulo 232 so the value is in the range 0 to 232−1; return values are also in this range.

When bits are numbered (as in bit32.extract), 0 is the least-significant bit (the one with value 20) and 31 is the most-significant (the one with value 231).

bit32.band
Returns the bitwise AND of its arguments: the result has a bit set only if that bit is set in all of the arguments.

If given zero arguments, the result has all bits set.

bit32.bnot
Returns the bitwise complement of.

bit32.bor
Returns the bitwise OR of its arguments: the result has a bit set if that bit is set in any of the arguments.

If given zero arguments, the result has all bits clear.

bit32.btest
Equivalent to

bit32.bxor
Returns the bitwise XOR of its arguments: the result has a bit set if that bit is set in an odd number of the arguments.

If given zero arguments, the result has all bits clear.

bit32.extract
Extracts  bits from , starting with bit. Accessing bits outside of the range 0 to 31 is an error.

If not specified, the default for  is 1.

bit32.replace
Replaces  bits in , starting with bit  , with the low   bits from. Accessing bits outside of the range 0 to 31 is an error.

If not specified, the default for  is 1.

bit32.lshift
Returns the number  shifted   bits to the left. This is a logical shift: inserted bits are 0. This is generally equivalent to multiplying by 2undefined.

Note that a displacement over 31 will result in 0.

bit32.rshift
Returns the number  shifted   bits to the right. This is a logical shift: inserted bits are 0. This is generally equivalent to dividing by 2undefined.

Note that a displacement over 31 will result in 0.

bit32.arshift
Returns the number  shifted   bits to the right. This is an arithmetic shift: if  is positive, the inserted bits will be the same as bit 31 in the original number.

Note that a displacement over 31 will result in 0 or 4294967295.

bit32.lrotate
Returns the number  rotated   bits to the left.

Note that rotations are equivalent modulo 32: a rotation of 32 is the same as a rotation of 0, 33 is the same as 1, and so on.

bit32.rrotate
Returns the number  rotated   bits to the right.

Note that rotations are equivalent modulo 32: a rotation of 32 is the same as a rotation of 0, 33 is the same as 1, and so on.

libraryUtil
This library contains methods useful when implementing Scribunto libraries. It may be loaded using

libraryUtil = require( 'libraryUtil' )

libraryUtil.checkType
Raises an error if  does not match. In addition, no error will be raised if  is nil and   is true.

is the name of the calling function, and  is the position of the argument in the argument list. These are used in formatting the error message.

libraryUtil.checkTypeMulti
Raises an error if  does not match any of the strings in the array.

This is for arguments that have more than one valid type.

libraryUtil.checkTypeForIndex
Raises an error if  does not match.

This is intended for use in implementing a  metamethod.

libraryUtil.checkTypeForNamedArg
Raises an error if  does not match. In addition, no error will be raised if  is nil and   is true.

This is intended to be used as an equivalent to  in methods called using Lua's "named argument" syntax,.

libraryUtil.makeCheckSelfFunction
This is intended for use in implementing "methods" on object tables that are intended to be called with the  syntax. It returns a function that should be called at the top of these methods with the  argument and the method name, which will raise an error of that   object is not.

This function will generally be used in a library's constructor function, something like this:

function myLibrary.new local obj = {} local checkSelf = libraryUtil.makeCheckSelfFunction( 'myLibrary', 'obj', obj, 'myLibrary object' ) function obj:method checkSelf( self, 'method' ) end function obj:method2 checkSelf( self, 'method2' ) end return obj end

luabit
The luabit library modules "bit" and "hex" may be loaded using

bit = require( 'luabit.bit' ) hex = require( 'luabit.hex' )

Note that the bit32 library contains the same operations as "luabit.bit", and the operations in "luabit.hex" may be performed using  and.

The luabit module "noki" is not available, as it is entirely useless in Scribunto. The luabit module "utf8" is also not available, as it was considered redundant to the Ustring library.

ustring
The pure-Lua backend to the Ustring library may be loaded using

ustring = require( 'ustring' )

In all cases the Ustring library should be used instead, as that replaces many of the slower and more memory-intensive operations with callbacks into PHP code.

Extension libraries
The following MediaWiki extensions provide additional Scribunto libraries:


 * Wikibase Client – provides access to Wikidata. See Extension:WikibaseClient/Lua.

Planned Scribunto libraries
These libraries are planned, or are in Gerrit pending review.


 * (none at this time)

Changed functions
The following functions have been modified:
 * setfenv
 * getfenv: May not be available, depending on the configuration. If available, attempts to access parent environments will fail.
 * getmetatable: Works on tables only to prevent unauthorized access to parent environments.
 * tostring: Pointer addresses of tables and functions are not provided. This is to make memory corruption vulnerabilities more difficult to exploit.
 * pairs
 * ipairs: Support for the __pairs and __ipairs metamethods (added in Lua 5.2) has been added.
 * pcall
 * xpcall: Certain internal errors cannot be intercepted.
 * require: Can fetch certain built-in modules distributed with Scribunto, as well as modules present in the Module namespace of the wiki. To fetch wiki modules, use the full page name including the namespace. Cannot otherwise access the local filesystem.

Removed functions and packages
The following packages are mostly removed. Only those functions listed are available:
 * package.*: Filesystem and C library access has been removed. Available functions and tables are:
 * package.loaded
 * package.preload
 * package.loaders: Loaders which access the local filesystem or load C libraries are not present. A loader for Module-namespace pages is added.
 * package.seeall


 * os.*: There are some insecure functions in here, such as os.execute, which can't be allowed. Available functions are:
 * os.clock
 * os.date
 * os.difftime
 * os.time


 * debug.*: Most of the functions are insecure. Available functions are:
 * debug.traceback

The following functions and packages are not available:
 * collectgarbage
 * module
 * coroutine.*: No application is known for us, so it has not been reviewed for security.
 * dofile
 * loadfile
 * io.*, file.*: Allows local filesystem access, which is insecure.
 * load
 * loadstring: These were omitted to allow for static analysis of the Lua source code. Also, allowing these would allow Lua code to be added directly to article and template pages, which was not desired for usability reasons.
 * print: This was discussed on wikitech-l and it was decided that it should be omitted in favour of return values, to improve code quality. If necessary, mw.log may be used to output information to the debug console.
 * string.dump: May expose private data from parent environments.

Additional caveats

 * Referential data structures: Circular data structures and data structures where the same node may be reached by more than one path cannot be correctly sent to PHP. Attempting to do so will cause undefined behavior. This includes (but is not limited to) returning such data structures from the module called by  and passing such data structures as parameters to Scribunto library functions that are implemented as callbacks into PHP. Such data structures may be used freely within Lua, including as the return values of modules loaded with.

Writing Scribunto libraries
This information is useful to developers writing additional Scribunto libraries, whether for inclusion in Scribunto itself or for providing an interface for their own extensions.

A Scribunto library will generally consist of five parts:
 * The PHP portion of the library.
 * The Lua portion of the library.
 * The PHP portion of the test cases.
 * The Lua portion of the test cases.
 * The documentation.

Existing libraries serve as a good example.

Library
The PHP portion of the library is a class that must extend. See the documentation for that class for implementation details. In the Scribunto extension, this file should be placed in, and a mapping added to. Other extensions should use the  hook. In either case, the key should match the Lua module name ("mw.name" for libraries in Scribunto, or "mw.ext.name" for extension libraries).

The Lua portion of the library sets up the table containing the functions that can be called from Lua modules. In the Scribunto extension, the file should be placed in. This file should generally include boilerplate something like this:

local object = {} local php function object.setupInterface( options ) -- Remove setup function object.setupInterface = nil -- Copy the PHP callbacks to a local variable, and remove the global php = mw_interface mw_interface = nil -- Do any other setup here -- Install into the mw global mw = mw or {} mw.ext = mw.ext or {} mw.ext.name = object -- Indicate that we're loaded package.loaded['mw.ext.name'] = object end return object

The module in  (load this with  ) contains some functions that may be helpful.

Be sure to run the Scribunto test cases with your library loaded, even if your library doesn't itself provide any test cases. The standard test cases include tests for things like libraries adding unexpected global variables. Also, if the library is loaded with PHP, any upvalues that its Lua functions have will not be reset between #invoke's. Care must be taken to ensure that modules can't abuse this to transfer information between #invoke's.

Test cases
The Scribunto extension includes a base class for test cases,, which will run the tests against both the LuaSandbox and LuaStandalone engines. The library's test case should extend this class, and should not override. In the Scribunto extension, the test case should be in  and added to the array in   (in  ); extensions should add the test case in their own   hook function, probably conditional on whether   is set.

Most of the time, all that is needed to make the test case is this:

class ClassNameTest extends Scribunto_LuaEngineTestBase { protected static $moduleName = 'ClassNameTest'; function getTestModules { return parent::getTestModules + array(             'ClassNameTest' => __DIR__ . '/ClassNameTests.lua';          ); } }

This will load the file  as if it were the page "Module:ClassNameTests", expecting it to return an object with the following properties:
 * count: Integer, number of tests
 * provide( n ): Function that returns three values:, the name of test  , and a string that is the expected output for test.
 * run( n ): Function that runs test  and returns one string.

If  is declared as shown, "Module:TestFramework" is available which provides many useful helper methods. If this is used,  would look something like this:

local testframework = require 'Module:TestFramework' return testframework.getTestProvider( {    -- Tests go here } )

Each test is itself a table, with the following properties:
 * name: The name of the test.
 * func: The function to execute.
 * args: Optional table of arguments to pass to the function.
 * expect: Results to expect.
 * type: Optional "type" of the test, default is "Normal".

The type controls the format of  and how   is called. Included types are:
 * Normal:  is a table of return values, or a string if the test should raise an error.   is simply called.
 * Iterator:  is a table of tables of return values.   is called as with an iterated for loop, and each iteration's return values are accumulated.
 * ToString: Like "Normal", except each return value is passed through.

Test cases in another extension
There are (at least) two ways to run PHPUnit tests:
 * 1) Run phpunit against core, allowing the tests/phpunit/suites/ExtensionsTestSuite.php to find the extension's tests using the UnitTestsList hook. If your extension's test class names all contain a unique component (e.g. the extension's name), the   option may be used to run only your extension's tests.
 * 2) Run phpunit against the extension directory, where it will pick up any file ending in "Test.php".

Either of these will work fine if Scribunto is loaded in LocalSettings.php. And it is easy for method #1 to work if Scribunto is not loaded, as the UnitTestsList hook can easily be written to avoid returning the Scribunto test when  is not set.

But Jenkins uses method #2. For Jenkins to properly run the tests, you will need to add Scribunto as a dependency for your extension. See for an example of how this is done.

If for some reason you need the tests to be able to run using method #2 without Scribunto loaded, one workaround is to add this check to the top of your unit test file:

if ( !isset( $GLOBALS['wgAutoloadClasses']['Scribunto_LuaEngineTestBase'] ) ) { return; }

Documentation
Modules included in Scribunto should include documentation in the Scribunto libraries section above. Extension libraries should include documentation in a subpage of their own Extension page, and link to that documentation from somewhere appropriate.

License
This manual is derived from the Lua 5.1 reference manual, which is available under the MIT license.

This derivative manual may also be copied under the terms of the same license.