Help:Parser function
Template:H:h A "parser function" is a template-like construct which returns a value based on at least one unnamed parameter, separated from the function name by a colon ":" (unlike ordinary templates using "|"). Thus the syntax is:
- {{functionname: argument 1 | argument 2 | argument 3...}}
or
- {{#functionname: argument 1 | argument 2 | argument 3...}}
The function name is not case-sensitive. Further parameters (if any, depending on the function) are separated by "|".
Core parser functions are built into MediaWiki. For backwards compatibility, they typically have no leading hash character. Extension parser functions, such as those provided by the ParserFunctions extension, typically have a leading hash character "#" to prevent collision with namespaces and interwiki prefixes.
MediaWiki's core parser functions are listed below.
Formatting
LC
Makes a text lowercase.
{{lc:AbCdEf}} gives abcdef.
{{lc:Ä Β Ç}} gives ä β ç, expected ä β ç.
UC
Makes a text uppercase.
{{uc:AbCdEf}} gives ABCDEF.
{{uc:ä β ß}} gives Ä Β SS, expected: Ä Β SS. Don't expect too much.
LCFIRST
Makes the first character lowercase: {{lcfirst:Ab Cd}} gives ab Cd.
UCFIRST
Makes the first character uppercase: {{ucfirst:aB cD}} gives AB cD.
URLENCODE
Converts the text into URL friendly format by replacing spaces with "+" and other url formatting characters with their escaped equivalents: {{urlencode:hello world ?&=#/:}} gives hello+world+%3F%26%3D%23%2F%3A.
NS
Gives the namespace name for a given namespace number or name:
{{ns:4}} gives Wikipedia.
{{ns:{{ns:12}}_talk}} gives Help talk.
{{ns:project}} gives Wikipedia.
However {{ns:{{SITENAME}}}} for {{SITENAME}}=Wikipedia doesn't work, on Meta it has the same effect as {{Meta}}, calling an existing Template:Meta.
Similarly {{ns:{{ns:8}} talk}} fails without underscore: MediaWiki talk. See Help:Variable for more canonical names like "project" and "talk".
NS:1
{{ns:{{ns:0}}_talk}} fails: Talk. The canonical name for the talk namespace of articles is "talk" and not "_talk". But the following constructs work:
{{ns:01}} gives Talk,
{{ns:+1}} gives Talk,
{{ns:TALK}} gives Talk, and
{{ns:{{ns:1}}}} gives also Talk. Space sensitive, but not case sensitive.
NS:0
'''#{{ns:0}}#''' gives ##, an empty string. This is often handy, less vulnerable than a template void or similar,
and less cryptic than magic words like __END__.
In constructs like {{ {{#if: {{{T|}}} | {{{T}}} | ns:0}} }}, where parameter T is
normally the name of a template to be evaluated, but can be undefined or empty, {{ns:0}}
is then a clean empty string. Without it {{}} would result in {{}}.
Please note that {{ns:{{ns:0}}}} fails: . NS cannot handle an empty {{ns:0}} argument.
An empty section title like above is obtained using, in this case, ==== {{ns:0}} ====. This is dubious, but arguably better than using the same trick to get invisble section headers twice on a page. At least /* {{ns:0}} */ makes sense in the edit history, if there's only one section using this particular trick.
As shown in the table of contents this and similar tricks result in non-functional links. In conjunction with __NOTOC__ it's less harmful, and maybe useful to get edit links for invisible sections with categories and interlanguage links. Other possibilities for different invisible section headers:
=== __NOTOC__ ====== ====== ======   ===
#language:
{{#language: code}} gives the language name of selected RFC 3066 language codes, otherwise it returns the input value as is. For a complete list see the IANA registry.
{{#language:da}} gives dansk{{#language:fo}} gives føroyskt{{#language:zh}} gives 中文{{#language:zh-min-nan}} gives 閩南語 / Bân-lâm-gú{{#language:ang}} gives Ænglisc{{#language:tlh}} gives tlh (missing, incomplete list){{#language:frr}} gives Nordfriisk (missing, introduced 2006){{#language:mw}} gives mw (no language code as of 2006)
This function will replace m:Template:n local (backlinks edit) and some of the Special:Prefixindex/Template:Lang name - templates.
For actually supported alpha2 and alpha3 codes see m:Template:sttnw (backlinks edit), the 27*26*26 template calls may take some time.
General features
The parameter value can be an expression involving (possibly multilevel): concatenation, applying a template or parser function, or using a variable.
Examples:
- using m:Template:tc (backlinks edit), {{uc:{{tc}}}} gives IN.
- using m:Template:x3 (backlinks edit), {{#expr:{{x3|1}}/3}} gives 37
Substitution
- See also: Help:Substitution.
Applying "subst:" to a parser function works:
{{subst:LC:AbC}} gives abc.
Note that unless a technique like optional recursive substitution
is used, substituting a template which uses a parser function does not replace that parser function with its result.
Terminology and history
Core parser functions were originally collectively unnamed in the MediaWiki codebase, although they were informally referred to simply as "functions" by developers. At some time around February 2006, editors of this documentation labelled them "colon functions", an unusual term which was unknown to the developers and the majority of users. In April 2006, the ParserFunctions extension was introduced, along with a new extension interface allowing efficient addition of arbitrary numbers of these entities, now labelled "parser functions". The syntax for the new parser functions was modelled on that of the old core parser functions, the main difference being the addition of the leading hash "#".
In July 2006, the parser function interface was extended to allow old-style hashless functions, and the old core parser functions were converted from using special-case code to the new parser function interface. They were moved to a CoreParserFunctions module. Thus today, there is no difference at all in syntax or functionality between core parser functions and extension parser functions, besides the leading hash convention.
Despite this, some users are in the habit of reserving the term "parser function" for members of the ParserFunctions extension. This is confusing and inaccurate -- any extension may define a parser function. The parser function interface has diverse applications. Perhaps it was confusing to call the extension ParserFunctions in the first place, but it was imagined as a fairly general repository of parser functions useful to Wikimedia.
See also