SBT: Run an action on all projects

You can define a project that aggregates all the other projects. Each action run on this project will be run on all aggregates. Here is an example from the sbt wiki:

import sbt._
import Keys._

object HelloBuild extends Build {
    lazy val root = Project(id = "hello",
                            base = file(".")) aggregate(foo, bar)

    lazy val foo = Project(id = "hello-foo",
                           base = file("foo"))

    lazy val bar = Project(id = "hello-bar",
                           base = file("bar"))
}