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Documentation for SCRIPT transformation (#1940) 

* Documentation for SCRIPT transformation

Signed-off-by: Jan N. Klug <github@klug.nrw>

* improvement

Signed-off-by: Jan N. Klug <github@klug.nrw>

* move to correct location

Signed-off-by: Jan N. Klug <github@klug.nrw>

* Apply suggestions from code review

Signed-off-by: Jerome Luckenbach <github@luckenba.ch>

Signed-off-by: Jan N. Klug <github@klug.nrw>
Signed-off-by: Jerome Luckenbach <github@luckenba.ch>
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@ -59,6 +59,54 @@ Transformation files need to be placed in the directory `$OPENHAB_CONF/transform
Transformations can be associated with channels, working on data being passed between bindings and Items. See [profile documentation]({{base}}/configuration/items.html#profiles) for more detail. Transformations can be associated with channels, working on data being passed between bindings and Items. See [profile documentation]({{base}}/configuration/items.html#profiles) for more detail.
To keep these examples simple, the contents of the referenced files `window_esp.map` and `convert-C-to-F.js` were left out. To keep these examples simple, the contents of the referenced files `window_esp.map` and `convert-C-to-F.js` were left out.
## `SCRIPT` Transformation
The `SCRIPT` transformation is available from the framework and needs no additional installation.
It allows transforming values using any of the available scripting languages in openHAB (JSR-223 or DSL).
The script needs to be placed in the `$OPENHAB_CONF/transform` folder with an extension `.script` regardless of the actual script type.
When referencing a transformation, the script type must be prepended to the filename (e.g. `dsl:stringlength` for the DSL version of `stringlength.script`).
Please note that you cannot have transformations with the same name and different languages as the file-extension is always `script`.
The input value is injected into the script context as a string variable `input`.
The result needs to be returned from the script, it can have be `null` or value of type that properly implements `.toString()`.
Additional parameters can be injected in the script by adding them to the script identifier in URL style (`js:scale?correctionFactor=1.1&divider=10` would also inject `correctionFactor` and `divider`).
The examples show a simple transformation with the same functionality for some languages.
It takes the length of the input string and e.g. returns `String has 5 characters`.
:::: tabs
::: tab DSL
The script-prefix is `dsl`.
```java
var returnValue = "String has " + input.length + " characters"
returnValue
```
:::
::: tab Nashorn JS
The script-prefix is `js`
```java
(function(data) {
var returnValue = "String has " + data.length + " characters"
return returnValue
})(input)
```
:::
::::
Currently the `SCRIPT` transformation is not available as profile.
More details regarding this and other Transformation services can be found in the individual transformation articles linked below. More details regarding this and other Transformation services can be found in the individual transformation articles linked below.
## Available Transformations ## Available Transformations