Script Task

## Script

### Description

Execute a script in a Apache BSF or JSR 223 supported language.

Note: This task depends on external libraries not included in the Apache Ant distribution. See Library Dependencies for more information.

The task may use the BSF scripting manager or the JSR 223 manager that is included in the JDK. This is controlled by the manager attribute. The JSR 223 scripting manager is indicated by javax.

All items (tasks, targets, etc) of the running project are accessible from the script, using either their name or id attributes (as long as their names are considered valid Java identifiers, that is). This is controlled by the setbeans attribute of the task. The name `project` is a pre-defined reference to the Project, which can be used instead of the project name. The name `self` is a pre-defined reference to the actual `<script>`-Task instance.
From these objects you have access to the Ant Java API, see the JavaDoc (especially for Project and Script) for more information.

If you are using JavaScript under BSF, a good resource is https://www.mozilla.org/rhino/doc.html as we are using their JavaScript interpreter.

Scripts can do almost anything a task written in Java could do.

Rhino provides a special construct—the `JavaAdapter`. With that you can create an object which implements several interfaces, extends classes and for which you can overwrite methods. Because this is an undocumented feature (yet), here is the link to an explanation: Google Groups: "Rhino, enum.js, JavaAdapter?" by Norris Boyd in the newsgroup netscape.public.mozilla.jseng.

If you are creating Targets programmatically, make sure you set the Location to a useful value. In particular all targets should have different location values.

### Parameters

Attribute | Description | Required
--- | --- | ---
language | The programming language the script is written in. Must be a supported Apache BSF or JSR 223 language | Yes
manager | Since Ant 1.7. The script engine manager to use. This can have one of three values: auto, bsf or javax. bsf use the BSF scripting manager to run the language. javax use the `javax.scripting` manager to run the language. auto use the BSF engine if it exists, otherwise use the `javax.scripting` manager. | No; default is auto
src | The location of the script as a file, if not inline | No
encoding | The encoding of the script as a file. Since Ant 1.10.2. | No; defaults to default JVM character encoding
setbeans | This attribute controls whether to set variables for all properties, references and targets in the running script. If this attribute is false, only the the `project` and `self` variables are set. If this attribute is true all the variables are set. Since Ant 1.7 | No; defaults to true
classpath | The classpath to pass into the script. Since Ant 1.7 | No
classpathref | The classpath to use, given as a reference to a path defined elsewhere. Since Ant 1.7 | No

### Parameters specified as nested elements

#### classpath

Since Ant 1.7

`Script`'s classpath attribute is a path-like structure and can also be set via a nested `<classpath>` element.

If a classpath is set, it will be used as the current thread context classloader, and as the classloader given to the BSF manager. This means that it can be used to specify the classpath containing the language implementation for BSF or for JSR 223 managers. This can be useful if one wants to keep `${user.home}/.ant/lib` free of lots of scripting language specific jar files.

Note: (since Ant 1.7.1) This classpath can be used to specify the location of the BSF jar file and/or languages that have engines in the BSF jar file. This includes the javascript, jython, netrexx and jacl languages.

### Examples

The following snippet shows use of five different languages:

        <property name="message" value="Hello world"/>

        <script language="groovy">
          println("message is " + message)
        </script>

        <script language="beanshell">
          System.out.println("message is " + message);
        </script>

        <script language="judoscript">
            println 'message is ', message
        </script>

        <script language="ruby">
            print 'message is ', $message, "\n"
        </script>

        <script language="jython">
    print "message is %s" % message
        </script>

Note that for the jython example, the script contents must start on the first column.

Note also that for the ruby example, the names of the set variables are prefixed by a $.

The following script shows a little more complicated JRuby example:

    <script language="ruby">
      xmlfiles = Dir.new(".").entries.delete_if { |i| ! (i =~ /\.xml$/) }
      xmlfiles.sort.each { |i| $self.log(i) }
    </script>

The same example in Groovy is:

    <script language="groovy">
      xmlfiles = new java.io.File(".").listFiles().findAll{ it =~ "\.xml$"}
      xmlfiles.sort().each { self.log(it.toString()) }
    </script>

The following example shows the use of classpath to specify the location of the beanshell jar file.

    <script language="beanshell" setbeans="true">
      <classpath>
        <fileset dir="${user.home}/lang/beanshell" includes="*.jar"/>
      </classpath>
      System.out.println("Hello world");
    </script>

The following script uses JavaScript to create a number of `echo` tasks and execute them.

    <project name="squares" default="main" basedir=".">
      <target name="main">
        <script language="javascript"> <![CDATA[
          for (i = 1; i <= 10; i++) {
            echo = squares.createTask("echo");
            echo.setMessage(i*i);
            echo.perform();
          }
        ]]> </script>
      </target>
    </project>

generates

    main:
    1
    4
    9
    16
    25
    36
    49
    64
    81
    100

    BUILD SUCCESSFUL

Now a more complex example using the Java API and the Ant API. The goal is to list the file sizes of all files a `<fileset/>` caught.

    <?xml version="1.0" encoding="UTF-8"?>
    <project name="MyProject" basedir="." default="main">

      <property name="fs.dir" value="src"/>
      <property name="fs.includes" value="**/*.txt"/>
      <property name="fs.excludes" value="**/*.tmp"/>

      <target name="main">
        <script language="javascript"> <![CDATA[
          // import statements
          // importPackage(java.io);
          importClass(java.io.File);
          // Nashorn syntax
          // load("nashorn:mozilla_compat.js");
          // or
          // var File = Java.type('java.io.File');

          // Access to Ant-Properties by their names
          dir      = project.getProperty("fs.dir");
          includes = MyProject.getProperty("fs.includes");
          excludes = self.getProject().getProperty("fs.excludes");

          // Create a <fileset dir="" includes=""/>
          fs = project.createDataType("fileset");
          fs.setDir(new File(dir));
          fs.setIncludes(includes);
          fs.setExcludes(excludes);

          // Get the files (array) of that fileset
          ds = fs.getDirectoryScanner(project);
          srcFiles = ds.getIncludedFiles();

          // iterate over that array
          for (i = 0; i < srcFiles.length; i++) {

            // get the values via Java API
            var basedir  = fs.getDir(project);
            var filename = srcFiles[i];
            var file = new File(basedir, filename);
            var size = file.length();

            // create and use a Task via Ant API
            echo = MyProject.createTask("echo");
            echo.setMessage(filename + ": " + size + " byte");
            echo.perform();
          }
        ]]></script>
      </target>
    </project>

We want to use the Java API. Because we don't want always typing the package signature we do an import. Rhino knows two different methods for import statements: one for packages and one for a single class. By default only the `java` packages are available, so `java.lang.System` can be directly imported with `importClass`/`importPackage`. For other packages you have to prefix the full classified name with Packages. For example Ant's `FileUtils` class can be imported with `importClass(Packages.org.apache.tools.ant.util.FileUtils)`

In Java 8 up until Java 14, you may use the built-in Nashorn JavaScript engine rather than Rhino (which is available in Java 7 runtime). Then, use `Java.type` as import statement for any Java class or the compatibility script: `load("nashorn:mozilla_compat.js");`.

Starting with Java 15 Nashorn has been removed again and you need to provide an external JavaScript engine. Your best option probably is GraalVM JavaScript which requires you to add a lot of extra jars. For GraalVM JavaScript 20.1 you'll need `org.graalvm.js:js`, `org.graalvm.js:js-engine` which in turn require `org.graalvm.regex:regex`, `org.graalvm.truffle:truffle-api`, `org.graalvm.sdk:graal-sdk`, and `com.ibm.icu:icu4j`. GraalVM JavaScript is not a drop-in replacement for Nashorn, see Graal's Nashorn Migration Guide for more details.

When using GraalVM JavaScript Ant will enable the feature `polyglot.js.allowAllAccess` in order to allow scripts to use Ant objects. By default it will also enable Nashorn compatibility mode, but you can disable this by setting the magic Ant property `ant.disable.graal.nashorn.compat` to `true`.

The `<script>` task populates the Project instance under the name `project`, so we can use that reference. Another way is to use its given name or getting its reference from the task itself. The Project provides methods for accessing and setting properties, creating DataTypes and Tasks and much more.
After creating a FileSet object we initialize that by calling its set-methods. Then we can use that object like a normal Ant task (`<copy>` for example).
For getting the size of a file we instantiate a `java.io.File`. So we are using normal Java API here.
Finally we use the `<echo>` task for producing the output. The task is not executed by its `execute()` method, because the `perform()` method (implemented in Task itself) does the appropriate logging before and after invoking `execute()`.

Here is an example of using beanshell to create an Ant task. This task will add filesets and paths to a referenced path. If the path does not exist, it will be created.

    <!--
           Define addtopath task
     -->
    <script language="beanshell">
        import org.apache.tools.ant.Task;
        import org.apache.tools.ant.types.Path;
        import org.apache.tools.ant.types.FileSet;
        public class AddToPath extends Task {
            private Path path;
            public void setRefId(String id) {
                path = getProject().getReference(id);
                if (path == null) {
                    path = new Path(getProject());
                    getProject().addReference(id, path);
                }
            }
            public void add(Path c) {
                path.add(c);
            }
            public void add(FileSet c) {
                path.add(c);
            }
            public void execute() {
                // Do nothing
            }
        }
        project.addTaskDefinition("addtopath", AddToPath.class);
    </script>

An example of using this task to create a path from a list of directories (using Ant-Contrib's <for> task) follows:

    <path id="main.path">
      <fileset dir="build/classes"/>
    </path>
    <ac:for param="ref" list="commons,fw,lps"
            xmlns:ac="antlib:net.sf.antcontrib">
      <sequential>
        <addtopath refid="main.path">
          <fileset dir="${dist.dir}/@{ref}/main"
                   includes="**/*.jar"/>
        </addtopath>
      </sequential>
    </ac:for>