Extension:Variables

MediaWiki extensions manual

Variables Release status: stable
Implementation	Parser function
Description	Introduces parser functions for dealing with page-scoped variables.
Author(s)	Rob Adams, Tom Hempel, Xiloynaha, Daniel Werner, MGChecker
Maintainer(s)	MGChecker
Latest version	2.5.1 (2019-07-11)
MediaWiki	1.29+
PHP	5.5+
Database changes	No
License	ISC License
Download	Download extension Git [?]: Browse repository (Phabricator · GitHub) Gerrit code review Git commit log Download source tarball README RELEASE-NOTES
Parameters $wgVariablesAreVolatile $wgVariablesDisabledFunctions
Hooks used ParserClearState ParserFirstCallInit
Quarterly downloads	93 (Ranked 41st)
Public wikis using	1,808 (Ranked 201st)
Translate the Variables extension if it is available at translatewiki.net
Vagrant role	variables
Issues	Open tasks · Report a bug

Warning:

This extension is incompatible with plans to parallelize parsing, as is intended by the use of Parsoid . Therefore, the future of this extension is uncertain, and it is expected to become incompatible with the standard MediaWiki parser within a few years. For further information, see T250963 and No support for sequential, in-order processing of extension tags .

To avoid deprecation warning about the InternalParseBeforeSanitize hook for MediaWiki 1.35 - MediaWiki 1.38 , or missing the #var_final parser function in MediaWiki 1.39 +, please update to the latest version (master branch for now). See T276627 and T250963 for further information.

The Variables extension allows you to define a variable on a page, use it later in that same page or included templates, change its value, possibly to a value given by an expression in terms of the old value, etc.

It is much like a template, only very lightweight and scoped to only a single page, so you can use many variables on a page without slowing down the wiki with huge numbers of templates. Combine this extension with the ParserFunctions extension for best results.

This extension will not be enabled for wikis run by the Wikimedia Foundation (WMF). See alternatives.

Assigning a value to a variable

#vardefine

• {{#vardefine:variablename | specifiedvalue }}

Assigns the value specifiedvalue to the (already existing or hereby introduced) variable variablename.

• Example: {{#vardefine:iconwidth|25}} making iconwidth = 25

#vardefineecho

• {{#vardefineecho:variablename | specifiedvalue }}

Works exactly as #vardefine, but the affected value is printed.

• Example: making iconwidth = {{#vardefineecho:iconwidth|25}}

Retrieving the value of a variable

#var

The value of the variable variablename is produced by

• {{#var:variablename}}

If undefined, this produces an empty string; it does not give an error message.

It is possible to get a default value for the case that the variable is undefined or void:

• {{#var:variablename | defaultvalue }}

This is equivalent to:

• {{#if: {{#var:variablename }} | {{#var:variablename }} | defaultvalue }}

but it is much shorter and better arranged. Before version 2.0 though, the default value always was expanded. From version 2.0 on the default only gets expanded in case it is actually used.

The value can be used in parser functions, etc.

#varexists

• {{#varexists:variablename }} returns 1 if the variable is already defined. If the variable is not defined the return value is void.

It supports a second and a third parameter to replace these values.

• {{#varexists:variablename | if-value | else-value }}

This is equivalent to:

• {{#if: {{#varexists: variablename }} | if-value | else-value }}

but it is much shorter and better arranged. Before version 2.5 though, both were always expanded. From version 2.5 on the if and else values only get expanded when their cases are actually entered.

#var_final

Experimental function introduced in Variables 2.0. This function will output the final, last value a variable has at the end of the page rendering. Naturally, the value will be inserted after the parser went over the entire wiki markup, so this function can't be used in other functions, expecting the right value is being used. Example:

• {{#var_final:variablename | defaultvalue }}

The default value will be used if the variable doesn't exist at the final page rendering stage or if its value is an empty string. The default will be expanded right where the function is used, so the parameter will be expanded, even if it won't be needed.

Examples

The ParserFunctions extension must also be installed to use #expr.

Compute x = 2*a + b:

• {{#vardefine:x|{{#expr:2*{{#var:a}}+{{#var:b}}}}}}

Add one to n:

• {{#vardefine:n|{{#expr:{{#var:n}}+1}}}}

Installation

• Download and move the extracted Variables folder to your extensions/ directory.
  Developers and code contributors should install the extension from Git instead, using:cd extensions/
git clone https://gerrit.wikimedia.org/r/mediawiki/extensions/Variables
• Add the following code at the bottom of your LocalSettings.php file:

  wfLoadExtension( 'Variables' );
  

• Configure as required
• Done – Navigate to Special:Version on your wiki to verify that the extension is successfully installed.

Configuration

This extension provides two configuration parameters:

$egVariablesAreVolatile

Allows to disable the parser frame being marked as volatile by the extension, i.e. disable template caching.

Default: true;

$egVariablesDisabledFunctions

Allows to disable specified parser functions provided by this extension.

Default: [];

Example: [ 'var_final', 'vardefineecho' ];

Compatibility

The recommended version of the Variables extension for recent MediaWiki releases is listed below. Older versions of the extensions might work as well, but aren't tested for new MediaWiki releases.

MediaWiki version	Variables version
1.19–1.22	2.1.x
1.23–1.28	2.2.x
1.29–1.34	2.5.x
1.35–1.39	2.5.x (deprecated)
1.40+	unsupported (WIP)

Alternatives

As this extension will not be enabled for wikis run by the Wikimedia Foundation (WMF), here are some alternatives:

• If you use Variables as cache for expensive operations, you can transform the section where you need them into a template and pass the required information as template parameters instead. This will work until you reach the expansion depth limit, which can be increased if necessary.
• If you use Variables to do more complex template operations than possible with simple Extension:ParserFunctions , and if you have sufficient permissions on the server, you can use Scribunto's Lua functionality instead. You may not be able to install Scribunto on shared hosting. Note that this does not add support for global Variables. However, Extension:VariablesLua adds a Scribunto interface for the Variables store.
• Don't use variables, instead duplicate the information you need as a variable. If that information is acquired by an expensive template call, performance may suffer. This will work until you reach the node count limit.
• If you require variables just for autonumbering, you could look into Extension:NumerAlpha .

See also

• Extension:PhpTags
• Extension:MyVariables – Creates new variables in the MediaWiki sense
• Extension:Loops – Provides parser functions for performing loops
• Extension:Arrays – Create an array and provide array functions (such as search, split, and sort) and set operations (such as intersect, union and diff)
• Extension:HashTables – New parser functions for handling hash tables in MediaWiki