Writing Expressions

Introduction

The Alkaline simple regular expressions extend mapping possibilities for search results. Extended tags, such as <!--name expression--> and options, such as <!--SET name--expression--> allow values in a special simple regexp form.

Expressions allow, for example, to show different output when no results were found. They also enable such advanced features as inserting a picture for search results from a particular location in the site. In either way, expressions help search templates designers to give their Alkaline users a look and feel of the site being searched.

Expression Variables

A variable name is a well defined entity beginning with a $ sign, followed by a series of alphanumeric elements, dots and dashes. Variables are used in Alkaline specific extended tags and options. For example, $url is a variable and is being translated into an url when used in a <!--SET MAP--expression--> option. For example:

<!--SET MAP--this is an url: $url-->

Variables use the following general syntax:

{$£}{name}[|COMMAND{PARAMETER}]~[Prefix]#[Postfix]^[Elsefix]

To output a variable value, simply use it with a $ sign, for example $url . To evaluate a variable, use it with a £ sign, for example £url~[Url is not empty!] . As you might have guessed, the final result will be "Url is not empty!" if the variable url contains any text and nothing will be output when it is empty.

Variable names can contain spaces and special characters. Such a variable should be used between brackets, for example $[Custom Meta Tag] .

In general, if the variable is empty, Elsefix is output. Otherwise, Prefix is inserted before and Postfix , after the variable value. Any of the three sections Prefix , Postfix or Elsefix can me omitted.

Expression Commands

Commands allow to pre-operate on the variable. This means that the variable value will be affected before it is checked for having any data for the Prefix , Postfix or Elsefix output. You can chain commands by separating them with a comma. Commands can be one, or a combination of the following:

Examples

The easiest way to understand how expressions work in Alkaline is to look at examples with the following data: