to run do >>>>>> rake excel:export

excel.rake

namespace :excel do
  desc "This task will export posts to excel sheet"
  task export: :environment do
      book = Spreadsheet::Workbook.new
      sheet = book.create_worksheet :name => 'Jobs'

      posts = Job.all

      posts.each_with_index do |post, i|
      sheet.row(i).push post.id, post.title, post.location, post.description
      end
      book.write 'Jobs.xls'
  end

end