my_tasks.rake

def pid_path
  "~/tmp/pid/"
end

def write_pid(name)
  `echo "#{Process.pid}" > #{pid_path}#{name}.pid`
  `echo "#{Process.ppid}" > #{pid_path}#{name}.ppid`
end

def delete_pid(name)
  `rm -rf #{pid_path}#{name}.pid`
  `rm -rf #{pid_path}#{name}.ppid`
end

def pid_task(*args, &block)
  task *args do |t|
    write_pid(t.name)
    block.call
    delete_pid(t.name)
  end
end

namespace :foo do

  pid_task :bar => :environment do
    Bla.blub
  end

end

rakectl.sh

#!/bin/bash

echo "${1} ${2}"
task=$1
cmd=$2

case $cmd in
   start)
      echo $$ > ~/tmp/pid/${task}.pid
      rake ${task}
      ;;
    stop)
      kill `cat ~/tmp/pid/${task}.ppid`
      kill `cat ~/tmp/pid/${task}.pid`
      rm -rf ~/tmp/pid/${task}.*
      ;;
    *)
      echo "usage: rakectl.sh your:task {start|stop}" ;;
esac
exit 0