Hook up a task to be invoked before publish-local

myBuild.scala

import sbt._
import Keys._

object MyBuild extends Build {

  lazy val beforeDeploy = TaskKey[Unit]("before-deploy", "will be invoked before deploy")

  val externalProcess = "echo $HOME"

  override lazy val settings: Seq[Setting[_]] = Seq[Setting[_]](
    beforeDeploy <<= streams map (out => externalProcess ! out.log),
    publishLocal <<= publishLocal dependsOn(beforeDeploy
  )

}