Ruby中扩展File

class File
  def self.write filename, content
    File.open(filename, 'wb') do |file|
      file.write content
    end
  end
  
  def self.append filename, content
    File.open(filename, 'ab') do |file|
      file.write content
    end
  end
 
  def self.expand_path_restricted(file_name, dir_string, restrict_dir_string = nil)
    dir_string = expand_path(dir_string)
    restrict_dir_string = restrict_dir_string ? expand_path(restrict_dir_string) : dir_string
 
    expanded = expand_path(file_name, dir_string)
 
    unless expanded.index(restrict_dir_string) == 0
      raise "Restricted file path #{file_name.inspect} must be inside #{restrict_dir_string.inspect}"
    end
    
    expanded
  end
end