build.gradle

apply plugin: GreetingPlugin

// Configure the 'greeting' extension object
greeting {
    // Configure its 'message' property
    message = 'Hi!'
}

class GreetingPlugin implements Plugin<Project> {

    void apply(Project project) {

        // Create the 'greeting' extension object
        project.extensions.create("greeting", GreetingPluginExtension)

        // Create a task that uses the configuration
        project.task('greet') << {
            println project.greeting.message
        }
    }
}

class GreetingPluginExtension {
    // Declare the 'message' property and assign it a default value
    def String message = 'Hello from GreetingPlugin'
}

/*** expected output ***\

    $ gradle greet
    :greet
    Hi!

    BUILD SUCCESSFUL

\***********************/