Help:Variable

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.

#vardefine


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

#vardefineecho


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

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:

This is equivalent to:

but it's much shorter and better arranged.

The value can be used in parser functions, etc.

#varexists

 * 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:

Add one to n: