Help:Variable

Related topics: Help:Contents, Wiki Templates

This function allows you to define a variable on a page, use it later in that same page, change its value, possibly to a value given by an expression in terms of the old value, etc.

It's much like a template, only very lightweight and scoped to only a single page, so you can use many variables on a page without polluting the wiki with huge numbers of templates.

• This function requires the Variables Extension be installed.

Assigning a value to a variable

#vardefine

{{#vardefine:variablename|specifiedvalue}}

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

#vardefineecho

{{#vardefineecho:variablename|specifiedvalue}}

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

Retrieving the value of a variable (#var)

The value of the variable variablename is produced by

{{#var:variablename}}

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

It's possible to define a 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's much shorter and better arranged.

The value can be used in parser functions, etc.

#varexists

{{#varexists:variablename}} returns 1 if the variable is already defined (also when the value is a void string). If the variable is not defined the return value is void.

Examples

Note that the ParserFunctions extension must also be installed to use #expr

Compute 2*a + b:

{{#expr:2*{{#var:a}}+{{#var:b}}}}

Add one to n:

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