1. Groovy : Groovy Shell

The Groovy Shell, aka. groovysh is a command-line application which allows easy access to evaluate Groovy expressions, define classes and run simple experiments.

1.1. Features

  • No need for go command to execute buffer.

  • Rich cross-platform edit-line editing, history and completion thanks to JLine2.

  • ANSI colors (prompt, exception traces, etc).

  • Simple, yet robust, command system with online help, user alias support and more.

  • User profile support

1.2. Command-line Options and Arguments

The shell supports several options to control verbosity, ANSI coloring and other features.

./bin/groovysh --help

Usage: groovysh [options] [...]
The Groovy Shell, aka groovysh, is a command-line application which allows easy
access to evaluate Groovy expressions, define classes and run simple
experiments.
  -C, --color[=<FLAG>]    Enable or disable use of ANSI colors
      -cp, -classpath, --classpath
                          Specify where to find the class files - must be first
                            argument
  -d, --debug             Enable debug output
  -D, --define=<name=value>
                          Define a system property
  -e, --evaluate=<CODE>   Evaluate the code first when starting interactive session
  -h, --help              Display this help message
  -pa, --parameters       Generate metadata for reflection on method parameter names
                            (jdk8+ only)
  -pr, --enable-preview   Enable preview Java features (jdk12+ only)
  -q, --quiet             Suppress superfluous output
  -T, --terminal=<TYPE>   Specify the terminal TYPE to use
  -v, --verbose           Enable verbose output
  -V, --version           Display the version

1.3. Evaluating Expressions

1.3.1. Simple Expressions

println "Hello"

1.3.2. Evaluation Result

When a complete expression is found, it is compiled and evaluated. The result of the evaluation is stored into the _ variable.

1.3.3. Multi-line Expressions

Multi-line/complex expressions (like closure or class definitions) may be defined over several lines. When the shell detects that it has a complete expression it will compile and evaluate it.

Define a Class
class Foo {
    def bar() {
        println "baz"
    }
}
Use the Class
foo = new Foo()
foo.bar()

1.3.4. Variables

Shell variables are all untyped (i.e. no def or other type information).

This will set a shell variable:

foo = "bar"

But, this will evaluate a local variable and will not be saved to the shell’s environment:

def foo = "bar"

This behavior can be changed by activating interpreter mode.

1.3.5. Functions

Functions can be defined in the shell, and will be saved for later use.

Defining a function is easy:

groovy:000> def hello(name) {
groovy:001> println("Hello $name")
groovy:002> }

And then using it is as one might expect:

hello("Jason")

Internally the shell creates a closure to encapsulate the function and then binds the closure to a variable. So variables and functions share the same namespace.

1.4. Commands

The shell has a number of different commands, which provide rich access to the shell’s environment.

Commands all have a name and a shortcut (which is something like \h). Commands may also have some predefined system aliases. Users may also create their own aliases.

1.4.1. Recognized Commands

help

Display the list of commands (and aliases) or the help text for specific command.

The Command List

groovy:000> :help

For information about Groovy, visit:
    http://groovy-lang.org

Available commands:
  :help      (:h ) Display this help message
  ?          (:? ) Alias to: :help
  :exit      (:x ) Exit the shell
  :quit      (:q ) Alias to: :exit
  import     (:i ) Import a class into the namespace
  :display   (:d ) Display the current buffer
  :clear     (:c ) Clear the buffer and reset the prompt counter
  :show      (:S ) Show variables, classes or imports
  :inspect   (:n ) Inspect a variable or the last result with the GUI object browser
  :purge     (:p ) Purge variables, classes, imports or preferences
  :edit      (:e ) Edit the current buffer
  :load      (:l ) Load a file or URL into the buffer
  .          (:. ) Alias to: :load
  :save      (:s ) Save the current buffer to a file
  :record    (:r ) Record the current session to a file
  :history   (:H ) Display, manage and recall edit-line history
  :alias     (:a ) Create an alias
  :set       (:= ) Set (or list) preferences
  :grab      (:g ) Add a dependency to the shell environment
  :register  (:rc) Register a new command with the shell
  :doc       (:D ) Open a browser window displaying the doc for the argument

For help on a specific command type:
    :help <command>

Help for a Command

While in the interactive shell, you can ask for help for any command to get more details about its syntax or function. Here is an example of what happens when you ask for help for the help command:

groovy:000> :help :help

usage: :help [<command>]

Display the list of commands or the help text for <command>.
exit

Exit the shell.

This is the only way to exit the shell. Well, you can still CTRL-C, but the shell will complain about an abnormal shutdown of the JVM.

import

Add a custom import which will be included for all shell evaluations.

This command can be given at any time to add new imports.

grab

Grab a dependency (Maven, Ivy, etc.) from Internet sources or cache, and add it to the Groovy Shell environment.

groovy:000> :grab 'com.google.guava:guava:19.0'
groovy:000> import com.google.common.collect.BiMap
===> com.google.common.collect.BiMap

This command can be given at any time to add new dependencies.

display

Display the contents of the current buffer.

This only displays the buffer of an incomplete expression. Once the expression is complete, the buffer is reset. The prompt will update to show the size of the current buffer as well.

Example

groovy:000> class Foo {
groovy:001> def bar
groovy:002> def baz() {
groovy:003> :display
 001> class Foo {
 002> def bar
 003> def baz() {
clear

Clears the current buffer, resetting the prompt counter to 000. Can be used to recover from compilation errors.

show

Show variables, classes or preferences or imports.

show variables

groovy:000> :show variables
Variables:
  _ = true

show classes

show imports

show preferences

show all

inspect

Opens the GUI object browser to inspect a variable or the result of the last evaluation.

purge

Purges objects from the shell.

purge variables

purge classes

purge imports

purge preferences

purge all

edit

Edit the current buffer in an external editor.

Currently only works on UNIX systems which have the EDITOR environment variable set, or have configured the editor preference.

load

Load one or more files (or urls) into the buffer.

save

Saves the buffer’s contents to a file.

record

Record the current session to a file.

record start

record stop

record status

history

Display, manage and recall edit-line history.

history show

history recall

history flush

history clear

alias

Create an alias.

doc

Opens a browser with documentation for the provided class.

For example, we can get both the Javadoc and GDK enhancements doc for java.util.List (shown running on JDK17):

groovy:000> :doc java.util.List
https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/List.html
https://docs.groovy-lang.org/4.0.12/html/groovy-jdk/java/util/List.html

This will print the documentation URLs found and open two windows (or tabs, depending on your browser):

  • one for the JDK documentation

  • one for the GDK documentation

By default, for Java classes, the java.base module is assumed. You can specify an optional module for other cases (shown running on JDK17):

groovy:000> :doc java.scripting javax.script.ScriptContext
https://docs.oracle.com/en/java/javase/17/docs/api/java.scripting/javax/script/ScriptContext.html

For backwards compatibility, if no module is specified when searching for Java classes, and no class is found in the java.base module, an additional attempt is made to find documentation for the class in the JDK8 (pre-module) Javadoc:

groovy:000> :doc javax.script.ScriptContext
https://docs.oracle.com/javase/8/docs/api/javax/script/ScriptContext.html

To get the Groovydoc for groovy.ant.AntBuilder and groovy.xml.XmlSlurper:

groovy:000> :doc groovy.ant.AntBuilder
https://docs.groovy-lang.org/4.0.12/html/gapi/groovy/ant/AntBuilder.html
groovy:000> :doc groovy.xml.XmlSlurper
https://docs.groovy-lang.org/4.0.12/html/gapi/groovy/xml/XmlSlurper.html

To get both the Groovydoc and GDK enhancements doc for groovy.lang.Closure and groovy.sql.GroovyResultSet:

groovy:000> :doc groovy.lang.Closure
https://docs.groovy-lang.org/4.0.12/html/gapi/groovy/lang/Closure.html
https://docs.groovy-lang.org/4.0.12/html/groovy-jdk/groovy/lang/Closure.html
groovy:000> :doc groovy.sql.GroovyResultSet
https://docs.groovy-lang.org/4.0.12/html/gapi/groovy/sql/GroovyResultSet.html
https://docs.groovy-lang.org/4.0.12/html/groovy-jdk/groovy/sql/GroovyResultSet.html

Documentation is also available for the GDK enhancements to primitive arrays and arrays of arrays:

groovy:000> :doc int[]
https://docs.groovy-lang.org/4.0.12/html/groovy-jdk/primitives-and-primitive-arrays/int%5B%5D.html
groovy:000> :doc double[][]
https://docs.groovy-lang.org/4.0.12/html/groovy-jdk/primitives-and-primitive-arrays/double%5B%5D%5B%5D.html
In contexts where opening a browser may not be desirable, e.g. on a CI server, this command can be disabled by setting the groovysh.disableDocCommand system property to true.
set

Set or list preferences.

1.5. Preferences

Some aspects of groovysh behaviors can be customized by setting preferences. Preferences are set using the set command or the := shortcut.

1.5.1. Recognized Preferences

interpreterMode

Allows the use of typed variables (i.e. def or other type information):

groovy:000> def x = 3
===> 3
groovy:000> x
===> 3

It’s especially useful for copy&pasting code from tutorials etc. into the running session.

verbosity

Set the shell’s verbosity level. Expected to be one of:

  • DEBUG

  • VERBOSE

  • INFO

  • QUIET

Default is INFO.

If this preference is set to an invalid value, then the previous setting will be used, or if there is none, then the preference is removed and the default is used.

colors

Set the shell’s use of colors.

Default is true.

show-last-result

Show the last result after an execution.

Default is true.

sanitize-stack-trace

Sanitize (trim-down/filter) stack traces.

Default is true.

editor

Configures the editor used by the edit command.

Default is the value of the system environment variable EDITOR.

To use TextEdit, the default text editor on macOS, configure: set editor /Applications/TextEdit.app/Contents/MacOS/TextEdit

1.5.2. Setting a Preference

groovy:000> :set verbosity DEBUG

1.5.3. Listing Preferences

To list the current set preferences (and their values):

groovy:000> :show preferences

Limitation: At the moment, there is no way to list all the known/available preferences to be set.

1.5.4. Clearing Preferences (i.e. Resetting to Defaults)

groovy:000> :purge preferences

1.6. User Profile Scripts and State

1.6.1. Profile Scripts

$HOME/.groovy/groovysh.profile

This script, if it exists, is loaded when the shell starts up.

$HOME/.groovy/groovysh.rc

This script, if it exists, is loaded when the shell enters interactive mode.

1.6.2. State

$HOME/.groovy/groovysh.history

Edit-line history is stored in this file.

1.7. Custom commands

The register command allows you to register custom commands in the shell. For example, writing the following will register the Stats command:

groovy:000> :register Stats

where the Stats class is a class extending the org.apache.groovy.groovysh.CommandSupport class. For example:

import org.apache.groovy.groovysh.CommandSupport
import org.apache.groovy.groovysh.Groovysh

class Stats extends CommandSupport {
    protected Stats(final Groovysh shell) {
        super(shell, 'stats', 'T')
    }

    public Object execute(List args) {
        println "Free memory: ${Runtime.runtime.freeMemory()}"
    }

}

Then the command can be called using:

groovy:000> :stats
stats
Free memory: 139474880
groovy:000>

Note that the command class must be found on classpath: you cannot define a new command from within the shell.

1.8. Troubleshooting

Please report any problems you run into. Please be sure to mark the JIRA issue with the Groovysh component.

1.8.1. Platform Problems

Problems loading the JLine DLL

On Windows, JLine2 (which is used for the fancy shell input/history/completion fluff), uses a tiny DLL file to trick the evil Windows faux-shell (CMD.EXE or COMMAND.COM) into providing Java with unbuffered input. In some rare cases, this might fail to load or initialize.

One solution is to disable the frills and use the unsupported terminal instance. You can do that on the command-line using the --terminal flag and set it to one of:

  • none

  • false

  • off

  • jline.UnsupportedTerminal

groovysh --terminal=none
Problems with Cygwin on Windows

Some people have issues when running groovysh with cygwin. If you have troubles, the following may help:

stty -icanon min 1 -echo
groovysh --terminal=unix
stty icanon echo

2. GMavenPlus Maven Plugin

GMavenPlus is a Maven plugin with goals that support launching a Groovy Shell or Groovy Console bound to a Maven project.

3. Gradle Groovysh Plugin

Gradle Groovysh Plugin is a Gradle plugin that provides gradle tasks to start a Groovy Shell bound to a Gradle project.