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Parser Functions are extensions to the MediaWiki software, mainly allowing IF statements.

Read more at http://meta.wikimedia.org/wiki/ParserFunctions


#expr

Expr simply computes a mathematical expression. It uses standard operators, including: + - * / = > < <= >= != <> as well as not, or, and, mod, round, and brackets ( ) can be used to group operations.

{{ #expr: expression }}

#if

The If statement shows something if the condition evaluates to anything other than zero, with the option of displaying alternative text.

{{ #if: <condition string> | <code if true> }}
{{ #if: <condition string> | <code if true> | <code if false> }}

Putting anything in the <condition string> will output the section. If the <condition string> is empty, null zero or white space, the <code if false> section will output (if it exists). If the <code if false> section is not included, and the <condition string> is null/zero/whitespace nothing will output.

#ifexist

Ifexist returns one of two results based on whether or not a particular page exists.

{{ #ifexist: <page name> | <page exists> | <page does not exist>  }}

Standard naming convention applies: the page Vehicles is accessible from Vehicles or vehicles, but not VEHICLES. Interwiki links and special pages will output as <page does not exist>.

#ifexpr

The function #ifexpr evaluates a mathematical expression (like #expr) and returns one of two strings depending on the result.

{{ #ifexpr: <expression> | <then text> | <else text>  }}

For example, {{ #ifexpr: 10 > 9 | yes | no }} outputs yes.

if expression is valid

If both the <then text> and <else text> are missing from #ifexpr, nothing is output except error messages (such as division by zero). This can be use with #if to determine if an expression is valid, rather than attempting to output the result:

{{ #if: {{#ifexpr: 1=2 }} | invalid | valid }}

The above expression is "valid". The condition will not output any error is a valid equation, so the output will be blank (as opposed to an error message). The if statement sees no output, so reports the <code if false> statement, which proves the expression is "valid".

If the expression was invalid (such as {{#ifexpr: 2/0 }}), then the #ifexpr would output an error message. The if statement would see positive output (not zero/null/whitespace) and so output the <code if true>. This proves the expression is "invalid".

#switch

The function #switch compares a single value against multiple others, returning a string if a match is found.

{{#switch: <comparison value>
 | <value1> = <result1>
 | <value2> = <result2>
 | ...
 | <valuen> = <resultn>
 | <default result>
 }}

If <comparison value> is <value1>, then <result1> will output. If it is <value2>, then <result2> will output. If it is none of these, then <default result> will output.

It is possible to have a fall-through, allowing multiple <values> to have one <result> entry:

{{#switch: <comparison value>
 | <value1>
 | <value2>
 | <value3> = <result1,2,3>
 | <default result>
 }}

If <comparison value> is <value1> or <value2> or <value3>, then <result1,2,3> will output.

String comparison is case-sensitive. To be made case-insensitive, use the Magic Word {{lc:}} to force everything to lowercase (or for upper case):

 {{ #switch: A | a=lower | A=UPPER  }} gives UPPER
 {{ #switch: {{lc:A}} | a=lower | A=UPPER  }} gives lower

#time

The function #time outputs the time, using a format string similar to that of PHP Date:

 {{ #time: format }}
 {{ #time: format | time }}

For example:

 {{ #time: l j F Y | 20070304 }} gives "Sunday 4 March 2007"
 {{ #time: l j F Y | -32 days }} gives "Sunday 6 April 2008" (32 days ago)
 {{ #time: H:i | +6 hours }} gives "20:17" (6 hours later than UTC)

#rel2abs

rel2abs converts a relative path to an absolute path:

 {{ #rel2abs: path }}
 {{ #rel2abs: path | base path }}
  • If standing in Help:Foo/bar and is calling {{ #rel2abs: ../baz }}, the result will be Help:Foo/baz
  • If standing in Help:Foo and is calling {{ #rel2abs: ../baz }}, the result will be baz

If you try to go up too many levels (an invalid relative path) an error will be output.

if relative path exists

This can be used in combination with #ifexist to determine whether a path exists:

 {{ #ifexist: {{#rel2abs: .. }} | '..' exist | '..' does not exist }} gives '..' does not exist
 {{ #ifexist: {{#rel2abs: . }} | '.' exist | '.' does not exist }} gives '.' exist


#titleparts

Titleparts returns a number of slash-separated segments of given a page name, starting from a specified segment.

{{ #titleparts: pagename | num | starting_from }}

This returns num slash-separated segments of pagename, starting from the specified starting segment.

 "{{#titleparts:Help:Link/a/b|0|}}" gives "Help:Link/a/b" 
 "{{#titleparts:Help:Link/a/b|2|}}" gives "Help:Link/a"
 "{{#titleparts:Help:Link/a/b|2|2}}" gives "a/b"
 "{{#titleparts:Help:Link/a/b|1|3}}" gives "b"
 "{{#titleparts:Help:Link/a/b|1|-1|}}" gives b


Notes

  • Applying "subst:" to a parser function works, provided that there is no space between "subst:" and "#".
  • The page to which #ifexist is applied (the page you're checking) is registered as link target of a link from the page with the #ifexist code on
  • div is not integer division and is redundant, use / (slash) for real divisions.
  • mod uses PHP's % operator, which is different from modulo-operators in all other programming languages, see also template:mod ( talk edit history links ) and 6068.
  • mod sometimes returns wrong results for the same input values, see 6356 and /MOD10000. Update: values less than 1E+12 are apparently not affected.
  • Under certain conditions round 0 results in -0 instead of 0. For an expression x using 0+(x) fixes this oddity.


Table Syntax

Currently wiki pipe table syntax doesn't work inside conditionals, but this can be worked around by using {{pipe}} to replace using | for the table syntax.

This extension is enabled by default on Wikia.

A "parser function" is a special piece of code in MediaWiki which extends the template functionality to perform logical operations. When rendered, parser functions use the parameters included in the definition to print out a specific result.

Parser functions are written out the same way templates are, surrounded by curly brackets. They are most easily identified by having either a colon or a hash sign (#) in the function name (or both, as is in the case of the {{#if:}} function).

A list of all parser functions for use on a wikia is visible at Special:Version.

Step-by-step use

  1. Identify the parser function that is appropriate for the task you are trying to do. There are a wide variety of parser functions, so be sure to do your research.
    Below this step-by-step is extra information with links to help direct you to full-fledged documentation of each parser function.
  2. Identify the proper syntax for the parser function you wish to use.
    In this step-by-step guide, we will be using the {{#ifexpr:}} (if expression) parser function, which is enabled on each Wikia wikia by default. Its syntax is:
    {{#ifexpr: expression | value if true | value if false }}
  3. Fill in the syntax.
    {{#ifexpr: 1 > 0 | yes | no }}
    In the example above, we filled in the mathematical expression (1 > 0), set the function to say "yes" if 1 > 0 is mathematically correct and say "no" if 1 > 0 is mathematically incorrect.
  4. Save the page and verify that the function seems to be returning the expected value. In our example, "yes" should be returned because 1 is indeed greater than 0.
    {{#ifexpr: 1 > 0 | yes | no }}yes.
    Note what would have happened if we had tweaked the expression but kept the returned values the same. The equation proves false because 0 is not greater than 1 and "no" is returned.
    {{#ifexpr: 1 < 0 | yes | no }}no.

While the above example might seem silly, because one should always know 1 > 0, the power of the parser function is revealed when it is passed a parameter. Let's say you are designing an infobox for a wikia about a TV show. You want to include a character's age and determine if they are an adult or not.

If within the infobox you have {{#ifexpr: {{{Age}}} >= 18 | This character is an adult. | This character is not an adult. }}, the code would say "This character is an adult" if the given age of the character is at or above 18. If the given age was less than 18, the code would instead say "this character is not an adult."

Built-in MediaWiki parser functions

The MediaWiki software itself includes multiple parser functions at the core. A full list of these are available here on MediaWiki.org. This page will illustrate the most useful.

{{fullurl:}}
Returns the full URL of a given page.
{{fullurl:Help:Contents}}/Help:Contents
{{#language:}}
Converts a language code to the language name.
{{#language:es}} → Español
{{lc:}}
Makes a string lowercase (opposite of {{uc:}}).
{{lc:CASE}} → case
{{ns:}}
Takes a namespace number and tells you what the namespace is.
{{ns:4}} → Community Central
{{plural:}}
If a given expression equals one, returns the singular value given. If a given expression equals two, returns the plural value given.
{{plural:1|is|are}} → is
{{plural:2|is|are}} → are

ParserFunctions Extension

Ifelselogic

The ParserFunctions extension relies on simple logic to return useful code.

The ParserFunctions extension is a popular MediaWiki extension that added a number of useful parser functions on top of the MediaWiki ones listed above. This extension is enabled by default across all of Wikia. This extension also include most of the parser functions found in the now deprecated extension StringFunctions, most notably {{#explode}}.

The ParserFunctions extension has functions for mathematical operations, if/else statements, and time functions. To view a complete list of these functions and extremely useful documentation on how to use them, please visit the extension's official help page.

Other Extensions

Quite a few other extensions that are popular on Wikia add some parser functions. Here are some common ones.

So if an extension you are interested in has a parser function included, please consult that extensions page on MediaWiki.org.

See also

Further help and feedback

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