Help:Extension:ParserFunctions

The  extension provides eleven additional parser functions to supplement the "", which are already present in MediaWiki.

(It may be configured to provide additional parser functions for string handling; these string functions are documented .)

All the parser functions provided by this extension take the form:

#expr
This function evaluates a mathematical expression and returns the calculated value.

This function is also available in  via the   function.



The available operators are listed to the right, in order of precedence. See 1>m:Special:MyLanguage/Help:Calculation|Help:Calculation for more details of the function of each operator. The accuracy and format of the result returned will vary depending on the operating system of the server running the wiki and the number format of the site language.

When evaluating using boolean algebra, zero evaluates to, and any nonzero value, positive or negative, evaluates to  :



An empty input expression returns an empty string. Invalid expressions return one of several error messages, which can be caught using the   function:



The order of addition and subtraction operands before or after a number is meaningful and may be treated as a positive or negative value instead of as an operand with an erroneous input:



Note, if using the output of magic words, you must raw-format them in order to remove commas and translate the numerals. For example,   results in , where we want 0, which can be obtained using  </>. This is especially important in some languages, where numerals are translated. For example, in Bengali, <tvar|numberofusers3> </> produces <tvar|bengali>৩০,০৬১</>.



Rounding
[<tvar|php>https://secure.php.net/function.round</> Rounds] off the number on the left to a multiple of 1/10 raised to a power, with the exponent equal to the truncated value of the number given on the right.

To round up or down use unary <tvar|ceil> </> or <tvar|floor> </> respectively.

Strings
Expressions only work with number-like values, they cannot compare strings or characters. <tvar|ifeq></> can be used instead.



#if
This function evaluates a test string and determines whether or not it is empty. A test string containing only white space is considered to be empty.





This function first tests whether the first parameter is not empty. If the first parameter is not empty the function displays the second argument. If the first parameter is empty or contains only whitespace characters (spaces, newlines, etc.) it displays the third argument.



The test string is always interpreted as pure text, so mathematical expressions are not evaluated:



The last parameter (false) may be omitted:



The function may be nested. To do so, nest the inner #if function in its full form in place of a parameter of the enclosing #if function. Up to seven levels of nesting is possible, although that may depend on the wiki or a memory limit.
 * <tvar|code1> </>

You can also use a parameter as the test string in your #if statement. You need to ensure you add the <tvar|pipe> </> (pipe symbol) after the name of the variable.

(So that if the parameter does not have a value, it evaluates to an empty string instead of the string " ".)


 * <tvar|code1> </>

See <tvar|1></> for more examples of this parser function.

#ifeq
This parser function compares two input strings, determines whether they are identical, and returns one of two strings based on the result. If more comparisons and output strings are required, consider using <tvar|switch> </>.



If both strings are valid numerical values, the strings are compared numerically:



Otherwise the comparison is made as text; this comparison is case sensitive:



(compare to similar example above, without the quotes) ''
 * →   (compare to similar example above, with <tvar|expr> </> returning a valid number first) 

As a practical example, consider an existing   using the parser to choose between two standard times, short and long. It takes the parameter as the first input to compare against the string "short" – there is no convention for the order, but it is simpler to read if the parameter goes first. The template code is defined as:



the following ensue:


 * → 20
 * → 40
 * → 40

#iferror
This function takes an input string and returns one of two results; the function evaluates to <tvar|true> </> if the input string contains an HTML object with <tvar|error> </>, as generated by other parser functions such as <tvar|expr> </>, <tvar|time> </> and <tvar|rel2abs> </>, templates>Special:MyLanguage/Help:Templates</>|template errors such as loops and recursions, and other "failsoft" parser errors.



One or both of the return strings can be omitted. If the  string is omitted, the   is returned if it is not erroneous. If the  string is also omitted, an empty string is returned on an error:


 * → &zwnj;
 * → &zwnj;
 * → &zwnj;
 * → &zwnj;
 * → &zwnj;
 * → &zwnj;

#ifexpr
This function evaluates a mathematical expression and returns one of two strings depending on the boolean value of the result:



The  input is evaluated exactly as for <tvar|expr> </> above, with the same operators being available. The output is then evaluated as a boolean expression.

An empty input expression evaluates to <tvar|false> </>:



As mentioned above, zero evaluates to <tvar|false> </> and any nonzero value evaluates to <tvar|true> </>, so this function is equivalent to one using <tvar|ifeq> </> and <tvar|expr> </> only:



except for an empty or wrong input expression (an error message is treated as an empty string; it is not equal to zero, so we get ).

comparing

Either or both the return values may be omitted; no output is given when the appropriate branch is left empty:



#ifexist
This function takes an input string, interprets it as a page title, and returns one of two values depending on whether or not the page exists on the local wiki.



The function evaluates to  if the page exists, whether it contains content, is visibly blank (contains meta-data such as category links or, but no visible content), is blank, or is a. Only pages that are redlinked evaluate to, including if the page used to exist but has been deleted.



The function evaluates to  for  that have been customized, and for  that are defined by the software.



If a page checks a target using <tvar|ifexist> </>, then that page will appear in the <tvar|spec-wth></> list for the target page. So if the code <tvar|code1> </> were included live on this page (<tvar|fullpagename1></>), wth></>/Foo will list <tvar|fullpagename2></>.

On wikis using a shared media repository, <tvar|ifexist> </> can be used to check if a file has been uploaded to the repository but not to the wiki itself:

If a local description page has been created for the file, the result is exists for all of the above.

<tvar|ifexist> </> does not work with interwiki links.

ifexist limits
<tvar|ifexist> </> is considered an "expensive parser function"; only a limited number of which can be included on any one page (including functions inside transcluded templates). When this limit is exceeded, any further <tvar|ifexist> </> functions automatically return false, whether the target page exists or not, and the page is categorized into <tvar|category>Category:</>. The name of the may vary depending on the content language of your wiki.

For some use cases it is possible to emulate the ifexist effect with css, by using the selectors  (to select links to unexisting pages) or   (to select links to existing pages). Furthermore, since the number of expensive parser functions that can be used on a single page is controlled by <tvar|ExpensiveParserFunctionsLimit> </>, one can also increase the limit in LocalSettings.php if needed.

ifexist and wanted pages
A page that does not exist and is tested for using #ifexist will end up on the Wanted Pages.

#rel2abs
This function converts a relative file path into an absolute filepath.


 * <tvar|code1> </>
 * <tvar|code3> </>

Within the  input, the following syntax is valid:
 * <tvar|code1> </> → the current level
 * <tvar|code2> </> → "go up one level"
 * <tvar|code3> </> → "go down one level into the subdirectory /foo"

If the <tvar|code1> </> is not specified, the full page name of the page will be used instead:


 * <tvar|code1> → '''</>
 * <tvar|code11> → '''</>
 * <tvar|code21> → '''</>
 * <tvar|code31> → '''</>

Invalid syntax, such as <tvar|code1> </> or <tvar|code2> </>, is ignored.

Since no more than two consecutive full stops are permitted, sequences such as these can be used to separate successive statements:


 * <tvar|code1> → '''</>
 * <tvar|code11> → '''</>
 * <tvar|code21> → '''</>
 * <tvar|code31> → '''</>

#switch
This function compares one input value against several test cases, returning an associated string if a match is found.

Examples:



<tvar|switch> # switch</> with partial transclusion tags can effect a configuration file that enables an editor unfamiliar with template coding to view and edit configurable elements.

Default
The  is returned if no   string matches the  :



In this syntax, the default result must be the last parameter and must not contain a raw equals sign (an equals sign without <tvar|1> </>).

If it does, it will be treated as a case comparison, and no text will display if no cases match.

This is because the default value has not been defined (is empty).

If a case matches however, its associated string will be returned.



Alternatively, the default result may be explicitly declared with a  string of " ".

Default results declared in this way may be placed anywhere within the function:



If the  parameter is omitted and no match is made, no   is returned:



Grouping results
It is possible to have 'fall through' values, where several  strings return the same   string. This minimizes duplication.

Here cases 2, 3 and 4 all return ; cases 6 and 7 both return.

The "<tvar|1> </>" in the last parameter may be omitted in the above case.

Use with parameters
The function may be used with parameters as the test string.

In this case, it is not necessary to place the pipe after the parameter name, because it is very unlikely that you will choose to set a case to be the string "<tvar|1> </>". ( This is the value the parameter will default to if the pipe is absent and the parameter doesn't exist or have a value.

See <tvar|1></>. )



In the above case, if <tvar|1> </> equals <tvar|2> </>, the function will return <tvar|3> </>.

If it equals <tvar|1> </>, the function will return <tvar|2> </>.

If the parameter is empty or does not exist, the function will return <tvar|1> </>.

As in the section above, cases can be combined to give a single result.



Here, if <tvar|1> </> equals <tvar|2> </>, <tvar|3> </> or <tvar|4> </>, the function will return <tvar|5> </>.

If it equals <tvar|1> </>, the function will return <tvar|2> </>.

If the parameter is empty or does not exist, the function will return <tvar|1> </>.

Additionally, the default result can be omitted if you do not wish to return anything if the test parameter value does not match any of the cases.



In this case, the function returns an empty string unless  exists and equals   or , in which case it returns   or  , respectively.

This has the same effect as declaring the default result as empty.



If for some reason you decide to set a case as " ", the function will return that case's result when the parameter doesn't exist or doesn't have a value. The parameter would have to exist and have a value other than the string " " to return the function's default result.


 * (when  doesn't exist or is empty):
 * →  Foo 
 * (when  has the value " "):
 * →  Bar 
 * (when  has the value " "):
 * →  Foo 

In this hypothetical case, you would need to add the pipe to the parameter.

Comparison behavior
As with <tvar|ifeq> </>, the comparison is made numerically if both the comparison string and the case string being tested are numeric; or as a case-sensitive string otherwise:





A  string may be empty:

Once a match is found, subsequent  are ignored:

Raw equal signs
"Case" strings cannot contain raw equals signs. To work around this, create a template <tvar|tpl>=</> containing a single equals sign: <tvar|code1> </>, or replace equals sign with html code <tvar|code2> </>.

Example:





Replacing #ifeq
can be used to reduce help>Special:MyLanguage/Help:Expansion depth</>|expansion depth.

For example:

is equivalent to

i.e. deep nesting, linear:

On the other hand, the switch replacement could be complicated/impractical for IFs nested in both branches (shown with alternatives of indentation, indented on both sides), making full symmetrical tree:

#time
This parser function takes a date and/or time (in the Gregorian calendar) and formats it according to the syntax given. A date/time object can be specified; the default is the value of the magic>Special:MyLanguage/Help:Magic words#Date and time</>|magic word <tvar|currenttimestamp> </> – that is, the time the page was last rendered into HTML.



The list of accepted formatting codes is given in the table to the right. Any character in the formatting string that is not recognized is passed through unaltered; this applies also to blank spaces (the system does not need them for interpreting the codes). There are also two ways to escape characters within the formatting string: In addition, the digraph  is interpreted as a single literal "x".
 * 1) A backslash followed by a formatting character is interpreted as a single literal character
 * 2) Characters enclosed in double quotes are considered literal characters, and the quotes are removed.



The  can be in any format accepted by PHP's <tvar|strtotime>strtotime</> function. Both absolute (eg ) and relative (eg  ) times are accepted.


 * &rarr; 
 * &rarr; 
 * &rarr; 
 * &rarr; 
 * &rarr; 
 * &rarr; 
 * &rarr; 

The  in ISO 639-3 (?) allows the string to be displayed in the chosen language



The <tvar|1> </> parameter specifies if the date/time object refers to the local timezone or to UTC.

This is a boolean parameters: its value is determined by casting the value of the argument (see the [<tvar|url>https://www.php.net/language.types.boolean#language.types.boolean.casting</> official PHP documentation] for details on how string are cast to boolean values).

See the following examples for details:





If you've calculated a Unix timestamp, you may use it in date calculations by pre-pending an  symbol.



Full or partial absolute dates can be specified; the function will "fill in" parts of the date that are not specified using the current values:



A four-digit number is always interpreted as a year, never as hours and minutes:



A six-digit number is interpreted as hours, minutes and seconds if possible, but otherwise as an error (not, for instance, a year and month):


 * →  Input is treated as a time rather than a year+month code.
 * →  Although 19:60:09 is not a valid time, 196009 is not interpreted as September 1960.

The function performs a certain amount of date mathematics:



The total length of the format strings of the calls of <tvar|time> </> is limited to 6000 characters.

Time Zone issue
There is a bug in this #time parser function (more specifically in PHP DateTime) that does not allow the passing-in of non-integers as relative time zone offsets. This issue does not apply when using an on-the-hour time zone, such as EDT. For example:


 * &rarr;

However, India is on a +5.5 hours time offset from UTC, and thus using its time zone will not normally allow the correct calculation of a relative time zone offset. Here's what happens:


 * &rarr;

To workaround this issue, simply convert the time into minutes or seconds, like this:


 * &rarr;
 * &rarr;

(Tim Starling, the developer of this function, provided the exact syntax for this solution.)

#timel
This function is identical to <tvar|time> </>, when the <tvar|2> </> parameter is set to <tvar|3> </>, so it always uses the local time of the wiki (as set in <tvar|1></>).

Syntax of the function is:





For instance, see the following examples:





#titleparts
This function separates a page title into segments based on slashes, then returns some of those segments as output.


 * <tvar|code0> </>

If the number of segments to return parameter is not specified, it defaults to "0", which returns all the segments from the first segment to return (included). If the first segment to return parameter is not specified or is "0", it defaults to "1":


 * →  See also.
 * →  See also.

Negative values are accepted for both values. Negative values for the number of segments to return parameter effectively 'strips' segments from the end of the string. Negative values for the first segment to return translates to "start with this segment counting from the right":


 * →  Strips one segment from the end of the string. See also <tvar|1></>.
 * →   Strips all 4 segments from the end of the string
 * →   Strips 5 segments from the end of the string (more than exist)
 * →   Returns last segment. See also <tvar|1></>.
 * →   Strips one segment from the end of the string, then returns the second segment and beyond
 * →   Start copying at the second last element; strip one segment from the end of the string

Before processing, the pagename parameter is HTML-decoded: if it contains some standard HTML character entities, they will be converted to plain characters (internally encoded with UTF-8, i.e. the same encoding as in the MediaWiki source page using this parser function).


 * For example, any occurrence of <tvar|q1> </>, <tvar|q2> </>, or <tvar|q3> </> in pagename will be replaced by <tvar|q> </>.
 * No other conversion from HTML to plain text is performed, so HTML tags are left intact at this initial step even if they are invalid in page titles.

Then the decoded pagename is canonicalized into a standard page title supported by MediaWiki, as much as possible:


 * 1) All underscores are automatically replaced with spaces:
 * →  Not bah_boo, despite the underscore in the original.
 * 1) The string is split a maximum of 25 times; further slashes are ignored and the 25th element will contain the rest of the string. The string is also limited to 255 characters, as it is treated as a page title:
 * If for whatever reason you needed to push this function to its limit, although very unlikely, it is possible to bypass the 25 split limit by nesting function calls:
 * 1) Finally the first substring is capitalized according to the capitalization settings of the local wiki (if that substring also starts by a local namespace name, that namespace name is also normalized).
 * 1) Finally the first substring is capitalized according to the capitalization settings of the local wiki (if that substring also starts by a local namespace name, that namespace name is also normalized).
 * 1) Finally the first substring is capitalized according to the capitalization settings of the local wiki (if that substring also starts by a local namespace name, that namespace name is also normalized).

{{Warning|1= Certain characters that are illegal in a page title will cause #titleparts to not parse the string:


 * → {{#titleparts: {one/two} | 1 | 1 }}. Does not produce the expected: {one
 * → {{#titleparts: page/123 | 1 | 2 }}. Does not work because brackets are illegal in page titles and this parser function does not process links embedded in its input pagename parameter, even when they use the MediaWiki syntax, or any other HTML or MediaWiki tags.
 * → "{{#titleparts: red/#00FF00/blue| 1 | 3 }}". Does not work because "#" is also illegal in page titles.

}}

StringFunctions
All of these functions (<tvar|1>, ,  ,  ,  ,  </>) are now 2>Special:Code/MediaWiki/50997</>|integrated into the <tvar|3>ParserFunctions</> extension, but are only available if an administrator sets <tvar|4> </> in <tvar|5> </>.

All of these functions operate in O(n) time complexity, making them safe against DoS attacks.

#len:
The <tvar|1>#len</> function returns the length of the given string.

The syntax is:

The return value is always a number of characters in the source string (after expansions of template invocations, but before conversion to HTML).

If no string is specified, the return value is zero.

#pos:
The <tvar|1>#pos</> function returns the position of a given search term within the string.

The syntax is:

The <tvar|1>offset</> parameter, if specified, tells a starting position where this function should begin searching.

If the search term is found, the return value is a zero-based integer of the first position within the string.

If the search term is not found, the function returns an empty string.

#rpos:
The <tvar|1>#rpos</> function returns the last position of a given search term within the string.

The syntax is:

If the search term is found, the return value is a zero-based integer of its last position within the string.

If the search term is not found, the function returns -1.

#sub:
The <tvar|1>#sub</> function returns a substring from the given string.

The syntax is:

The <tvar|1>start</> parameter, if positive (or zero), specifies a zero-based index of the first character to be returned.

Example:

<tvar|1> </> returns <tvar|2> </>.

<tvar|1> </> returns <tvar|2> </>.

If the <tvar|1>start</> parameter is negative, it specifies how many characters from the end should be returned.

Example:

<tvar|1> </> returns <tvar|2> </>.

The <tvar|1>length</> parameter, if present and positive, specifies the maximum length of the returned string.

Example:

<tvar|1> </> returns <tvar|2> </>.

If the <tvar|1>length</> parameter is negative, it specifies how many characters will be omitted from the end of the string.

Example:

<tvar|1> </> returns <tvar|2> </>.

If the <tvar|1>start</> parameter is negative, it specifies how many characters from the end should be returned.

The <tvar|1>length</> parameter, if present and positive, specifies the maximum length of the returned string from the starting point.

Example:

<tvar|1> </> returns <tvar|2> </>.

#replace:
The #replace function returns the given string with all occurrences of a search term replaced with a replacement term.

If the search term is unspecified or empty, a single space will be searched for.

If the replacement term is unspecified or empty, all occurrences of the search term will be removed from the string.

Currently the syntax doesn't provide a switch to toggle case-sensitivity setting. But you may make use of magic words of formatting (e.g. your_string_here ) as a workaround. For example, if you want to remove the word "Category:" from the string regardless of its case, you may type:
 * Case-insensitive replace

But the disadvantage is that the output will become all lower-case. If you want to keep the casing after replacement, you have to use multiple nesting levels (i.e. multiple replace calls) to achieve the same thing.

#explode:
The #explode function splits the given string into pieces and then returns one of the pieces. The syntax is:

The delimiter parameter specifies a string to be used to divide the string into pieces. This delimiter string is then not part of any piece, and when two delimiter strings are next to each other, they create an empty piece between them. If this parameter is not specified, a single space is used. The limit parameter is available in ParserFunctions only, not the standalone StringFunctions version, and allows you to limit the number of parts returned, with all remaining text included in the final part.

The position parameter specifies which piece is to be returned. Pieces are counted from 0. If this parameter is not specified, the first piece is used (piece with number 0). When a negative value is used as position, the pieces are counted from the end. In this case, piece number -1 means the last piece. Examples:


 * returns.
 * returns.
 * returns.
 * returns.

The return value is the position-th piece. If there are fewer pieces than the position specifies, an empty string is returned.

Limits
This module defines three global settings:


 * 
 * 
 * 

These are used to limit some parameters of some functions to ensure the functions operate in O(n) time complexity, and are therefore safe against DoS attacks.

$wgStringFunctionsLimitSearch
This setting is used by #pos, #rpos, #replace, and #explode. All these functions search for a substring in a larger string while they operate, which can run in O(n*m) and therefore make the software more vulnerable to DoS attacks. By setting this value to a specific small number, the time complexity is decreased to O(n).

This setting limits the maximum allowed length of the string being searched for.

The default value is 30 multibyte characters.

$wgStringFunctionsLimitReplace
This setting is used by #replace. This function replaces all occurrences of one string for another, which can be used to quickly generate very large amounts of data, and therefore makes the software more vulnerable to DoS attacks. This setting limits the maximum allowed length of the replacing string.

The default value is 30 multibyte characters.

Substitution
Parser functions can be help>Special:MyLanguage/Help:Substitution</>|substituted by prefixing the hash character with <tvar|subst> </>:


 * → the code   will be inserted in the wikitext since the page exists.

Substitution does not work within <tvar|code1></>, you can use <tvar|code2> &hellip; </> for this purpose.

Redirects
Especially <tvar|time> </> could be handy in  to pages including dates, but this does not work.

Escaping pipe characters in tables
Parser functions will mangle syntax and pipe characters (<tvar|pipe> </>), treating all the raw pipe characters as parameter dividers. To avoid this, most wikis used a template <tvar|template>   :!</> with its contents only a raw pipe character (<tvar|pipe> </>), since MW 1.24 a  replaced this kludge. This 'hides' the pipe from the MediaWiki parser, ensuring that it is not considered until after all the templates and variables on a page have been expanded. It will then be interpreted as a table row or column separator. Alternatively, raw HTML table syntax can be used, although this is less intuitive and more error-prone.

You can also escape the pipe character for display as a plain, uninterpreted character using an HTML entity: <tvar|entity> </>.

Stripping whitespace
Whitespace, including newlines, tabs, and spaces, is stripped from the beginning and end of all the parameters of these parser functions. If this is not desirable, comparison of strings can be done after putting them in quotation marks.



To prevent the trimming of then and else parts, see <tvar|meta-tpl-if>m:Template:If</>. Some people achieve this by using &lt; &gt;  &lt; /nowiki &gt; instead of spaces.


 * → foofoo
 * → foofoo

However, this method can be used to render a single whitespace character only, since the parser squeezes multiple whitespace characters in a row into one.




 * || → || foofoo 
 * }

In this example, the  style is used to force the whitespace to be preserved by the browser, but even with it the spaces are not shown. This happens because the spaces are stripped by the software, before being sent to the browser.

It is possible to workaround this behavior replacing whitespaces with  (breakable space) or   (non-breakable space), since they are not modified by the software:


 * →  foofoo 
 * → foofoo