# Script

## ![](/files/nqGIyOd8aknczvu1Gifx) Script

### Description <a href="#description" id="description"></a>

The Script transform allows you to write code in any language supported by the [JSR-223](https://en.wikipedia.org/wiki/Scripting_for_the_Java_Platform) standard.

By default, the Hop project ships with the following language support:

* [Groovy](https://groovy-lang.org/)
* [Python](https://www.python.org/) ([Jython](https://www.jython.org/))

{% hint style="info" %}
Warning: ECMAScript (JavaScript as part of the JVM) was removed from the JVM with Java 17. You can still add it in Apache Hop 2.10 and later as documented in the [Adding Scripting Languages](#_adding_scripting_languages) section.
{% endhint %}

### Options

| Option         | Description                                                                                                                                                                                                                                                                                                                                                                                   |
| -------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Transform name | Name of the transform this name has to be unique in a single pipeline.                                                                                                                                                                                                                                                                                                                        |
| Script engine  | You can choose any of the discovered JSR-223 scripting engines from the drop-down list.                                                                                                                                                                                                                                                                                                       |
| Script         | <p>You can add one or more scripts. There are different types of scripts which you can change by right-clicking on the script tab.</p><p><code>Transform</code> : The script will be executed after every row that is read. <code>Start</code>: The script will be executed once at the start of the transform. <code>End</code>: The script will be executed after the last row was read</p> |
| Fields         | Here you can specify the fields to retrieve from the context of the transform script after every row.                                                                                                                                                                                                                                                                                         |

### Variable bindings

To allow you to work with the input field values or the surrounding Java ecosystem Hop exposes a bunch of variable bindings.

| Variable          | Description                                                                                                                                                                                                                                                                                                                                                                              |
| ----------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| input             | All the input fields under their own name. Please note that certain scripting languages have restrictions on the allowed names of variables. Make sure to rename inappropriate field names with a "Select Values" transform.                                                                                                                                                             |
| `transform`       | This is a reference to the parent transform class [Script](https://github.com/apache/hop/blob/master/plugins/transforms/abort/src/main/java/org/apache/hop/pipeline/transforms/script/Script.java). You can use this to log certain important events or write extra output rows                                                                                                          |
| `pipeline_status` | <p>This special variable can be set to any of the following values:</p><p><code>CONTINUE\_PIPELINE</code>: Process the current row and generate output (the default value) <code>SKIP\_PIPELINE</code> : Do not write an output row <code>STOP\_PIPELINE</code> : Cause the pipeline to stop processing rows <code>ERROR\_PIPELINE</code>: Cause the pipeline to abort with an error</p> |
| `rowNumber`       | This is the current row number, starting from 1.                                                                                                                                                                                                                                                                                                                                         |
| `rowMeta`         | The input row metadata. It’s a list of value metadata.                                                                                                                                                                                                                                                                                                                                   |
| `row`             | <p>An object array containing the current set of field values. Make sure to address these values using <code>rowMeta</code> to make sure the appropriate data conversions take place.</p><p>For example, use <code>rowMeta.getString(row, 0)</code> to get the first String value from the input row.</p>                                                                                |
| `previousRow`     | The previous row or null if `row` is the first input row.                                                                                                                                                                                                                                                                                                                                |
| `transformName`   | The name of the transform                                                                                                                                                                                                                                                                                                                                                                |
| `pipelineName`    | The name of the pipeline                                                                                                                                                                                                                                                                                                                                                                 |

### Generating rows

Below are scripts that generate 10 output rows using a simple loop in 3 different scripting engines. This happens 3 times with identical output. For the 3 examples you need to define 2 output fields:

* `id` : an Integer
* `name` : a String

#### ECMAScript

```highlight
var Long = Packages.java.lang.Long;
var RowDataUtil = Packages.org.apache.hop.core.row.RowDataUtil;

var START=100000;
var COUNT=10;
var END=START+COUNT;
var id=START;

for (var id=START;id<END;id++) {
  var outputRow = RowDataUtil.allocateRowData(rowMeta.size());
  outputRow[0] = new Long(id);
  outputRow[1] = "Apache Hop "+id;
  transform.putRow(outputRowMeta, outputRow);
}

pipeline_status=SKIP_PIPELINE;
```

#### Groovy

```highlight
def COUNT=10;

id = 100000L;
(1..COUNT).each {
 outputRow = RowDataUtil.allocateRowData(rowMeta.size());
 outputRow[0] = id;
 outputRow[1] = "Apache Hop "+id
 transform.putRow(outputRowMeta, outputRow);

 id++;
}

pipeline_status=SKIP_PIPELINE;
```

#### Python

```highlight
import java.lang.Long as Long

START=100000
COUNT=10
END=START+COUNT
id=START

for id in range(START,END):
    outputRow = RowDataUtil.allocateRowData(rowMeta.size())
    outputRow[0] = Long(id)
    outputRow[1] = "Apache Hop "+str(id)
    transform.putRow(outputRowMeta, outputRow)

pipeline_status=SKIP_PIPELINE
```

### Aggregating rows

Below are scripts that aggregate rows over different groups. The data is sorted by the field `group` and contains a `value` field which is summed up into field `sum`. In the start scripts we define variables `sum=0` and `previousGroup=""`.

For the 3 examples you need to define 1 output field:

* `sum` : an Integer

#### ECMAScript

```highlight
if (group!==previousGroup) {
  sum=value;
  previousGroup=group;
} else {
  sum+=value;
}

if (nextGroup==null) {
  pipeline_status=CONTINUE_PIPELINE;
} else {
  pipeline_status=SKIP_PIPELINE;
}
```

#### Groovy

```highlight
if (!group.equalsIgnoreCase(previousGroup)) {
  sum=value;
  previousGroup=group;
} else {
  sum+=value;
}

if (nextGroup==null) {
  pipeline_status=CONTINUE_PIPELINE;
} else {
  pipeline_status=SKIP_PIPELINE;
}
```

#### Python

```highlight
if group!=previousGroup:
  sum=value
  previousGroup=group
else:
  sum=sum+value

if nextGroup is None:
  pipeline_status=CONTINUE_PIPELINE
else:
  pipeline_status=SKIP_PIPELINE;
```

### Adding scripting languages

You can add additional scripting languages by adding the required libraries to the `plugins/transforms/script/lib` folder.

For example, to add support for the Ruby scripting language you need to add the following [JRuby libraries](https://mvnrepository.com/artifact/org.jruby):

* `jruby-stdlib-<version>.jar`
* `jruby-core-<version>.jar`

To add Javascript support, download the [Nashorn Core jar](https://repo1.maven.org/maven2/org/openjdk/nashorn/nashorn-core/)

* `nashorn-core-15.4.jar`

After restarting the Apache Hop GUI you’ll notice that there’s a `ruby` or `Javascript` entry in the `Scripting Engine` dropdown box.


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