Please expain the syntax of the gradle task definition "<<"

Question

The Gradle User Guide shows a syntax for creating a task that I don't understand:

task hello << {
    println 'Hello world!'
}

What is the << doing there?
The question/answer was a little enlightening but I still don't know exactly what << is. Is << a groovy thing or a gradle thing?

Answer 1

Bob's answer covers the Groovy side. For the Gradle portion, << corresponds to doLast on task, adding another action to the end of the task's list of actions.

Answer 2

It's a groovy thing. Operators can be overloaded in Groovy by declaring a method on the object the operator is applied on. In this case, the method is leftShift().

See http://groovy.codehaus.org/Operator+Overloading for more information.