# lets you edit file contents and save to other file
# usage:
# 
# edit_file_contents 'file.template', 'file' do |contents|
#   contents.gsub!(/alpha(.)*/, 'beta')
# end
# 
# and the modified contents will be saved in 'dst' file
def edit_file_contents src, dst
  raise "No block given" if ! block_given?
  
  contents = ""
  File.open( src, 'r' ) do |file|
    contents = file.read
  end

  yield contents
  
  File.open( dst, 'w' ) do |file|
    file.write contents
  end
end