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 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,   produces 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.


 * <tvar|code1> </>

See 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.

#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.



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

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:





For a simple real life example of the use of this function, check [<tvar|enwp-nba-color>https://en.wikipedia.org/w/index.php?title=Template:NBA_color&action=edit&oldid=600531646</> Template:NBA color]. Two complex examples can be found at <tvar|tpl-ext></> and [<tvar|enwp-botreq>http://en.wikipedia.org/wiki/Template:BOTREQ</> Template:BOTREQ].

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

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:

However, Venezuela is on a -4.5 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:

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

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

#timel
This function is identical to <tvar|time> </>, except that it uses the local time of the wiki (as set in <tvar|1></>) when no date is given.





#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.
 * →   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.
 * →   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 occurence 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.

}}

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