Introduction

• A variable is a snippet of text that can be accessed by name.
• The text is referred to as the variable's value.

Variables are defined by widgets. Several core widgets define variables, the most common being the $let, $set and $list widgets.

The values of variables are available to descendant widgets, including transcluded content. For example, within each tiddler in the main story river the variable currentTiddler is set to the title of the tiddler.

Variables can also be overwritten by descendent widgets defining variables of the same name, thus binding a different snippet to that name for the scope of the children of the widget.

Special Kinds of Variables

There are several special kinds of variable that extend their basic capabilities:

• Procedures are snippets of text that can be passed parameters when wikified
• Functions are snippets of text containing filters with optional named parameters
• Custom Widgets are snippets of text containing definitions of custom widget
• Macros are snippets of text that can contain placeholders that are filled in with parameters whenever the macro is used

Note that these special kinds of variable can only be created with the associated shortcut definition syntax.

For a more detailed comparison of these special kinds of variables, see Variable Usage.

Defining Variables

The following core widgets are commonly used to define variables:

• $let widget – the easiest way to define multiple variables
• $set widget – the most flexible way to define a single variable
• $parameters widget – used to declare parameter variables within procedures and custom widgets
• $list widget – defines a loop variable and optional counter variable
• $setmultiplevariables widget – allows creation of multiple variables at once where the names and values are not known in advance

Using Variables

Once a variable is defined there are several ways to access it.

Transcluding Variables

Transcluding a variable renders the text contents of the variable as if it replaced the call. It is a shortcut syntax for the $transclude widget with the $variable attribute.

<<varname>>

Parameters can be passed to the transclusion as follows:

<<varname "This is a parameter">>
<<varname param:"This is a parameter">>
<<varname param:"This is a parameter" second:"Another parameter">>

The handling of these parameters depends on the kind of variable:

• Procedures assign the parameters to variables that are available within the procedure
• Macros replace the text of the special markers $param$ with the values passed to the macro for those parameters (see Macro Parameter Handling for the details)

The parameters are ignored for other kinds of variable.

Macro Variable Substitutions

Before the text of a macro is used, the special markers $(variable)$ are replaced with the values of the named variable.

Variable Attributes

Variables can be used as the value of attributes of widgets or HTML elements:

<div class=<<varname>>>

Parameters can be passed:

<div class=<<varname "This is a parameter">>>
...
<div class=<<varname param:"This is a parameter">>>
...
<div class=<<varname param:"This is a parameter" second:"Another parameter">>>
...

The handling of these parameters depends on the kind of variable:

• Functions assign the parameters to variables that are available within the function
• Macros replace the text of the special markers $param$ with the values passed to the macro for those parameters (see Macro Parameter Handling for the details)

The parameters are ignored for other kinds of variable.

Variables in Filters

Variables can be accessed within Filters using angle brackets to quote the name:

[<varname>]

Parameters can be passed in the usual way:

[<varname "This is a parameter">]
[<varname param:"This is a parameter">]
[<varname param:"This is a parameter" second:"Another parameter">]
...

See Also

• The dumpvariables macro lists all variables that are available at that position in the widget tree
• Complete listing of TiddlyWiki's built-in Core Variables

Examples

Example of Defining a Variable

<$set name=animal value=zebra>
<<animal>>
</$set>

Example of Defining a Macro

The \define pragma below defines a macro called tags-of-current-tiddler. The macro returns the value of the tiddler's tags field, and can be accessed from anywhere else in the same tiddler (or in any tiddler that imports it).

\procedure tags-of-current-tiddler() {{!!tags}}

The tags are: <<tags-of-current-tiddler>>

Example of Using a Variable as a Filter Parameter

This example uses the backlinks operator to list all tiddlers that link to this one.

<<list-links filter:"[<currentTiddler>backlinks[]]">>