Scripts

How to use scripts in openHAB

Introduction

openHAB comes with a very powerful expression language, which can be used to define scripts. A script is a code block that can be defined by the user and which can be called and thus reused from different places.

Defining Scripts

File Location

Scripts are placed in the folder {{{${openhab.home}/configurations/scripts}}}. The runtime already comes with a demo file called {{{demo.script}}}. The filename defines the name of the script (without its extension) for references.

The Syntax

The expression language used within scripts is the same that is used in the Xtend language - see the documentation of expressions on the Xtend homepage.

The syntax is very similar to Java, but has many nice features that allows writing concise code. It is especially powerful in handling collections. What makes it a good match for openHAB from a technical perspective is the fact that there is no need to compile the scripts as they can be interpreted at runtime.

Variables and Functions

To be able to do something useful with the scripts, openHAB provides access to

• all defined items, so that you can easily access them by their name
• all enumerated states/commands, e.g. {{{ON, OFF, DOWN, INCREASE}}} etc.
• all standard actions to make something happen

Combining these features, you can easily write code like if(Temperature.state < 20) { sendCommand(Heating, ON) }

IDE Support

The openHAB Designer offers full IDE support for scripts, which includes syntax checks and coloring, validation with error markers, content assist (Ctrl+Space) etc. This makes the creation of scripts very easy!

http://wiki.openhab.googlecode.com/hg/images/screenshots/designer-scripts.png

Calling Scripts

A script is identified by its filename. If the filename is {{{demo.script}}}, the script name is simply {{{demo}}}. Every script has a return value, which is the result of the last expression in it (and might be {{{null}}}).

Scripts can be called from different places:

• From within rules through the {{{callScript("")}}} Actions.
• From a calendar entry in your Google calendar - just put {{{> callScript("")}}} in the entry
• From inside the XMPP console by typing {{{> callScript("")}}}

Note that you can put any expression behind the ">" sign, calling a script is just one option. Therefore you could ask for the current temperature in the XMPP console like this: > Temperature.state

In future, there might also be the possibility to use scripts for transformations (e.g. for defining label texts) or in command mappings.