class String
  def trim!(chars)
    rtrim!(chars)
    ltrim!(chars)
  end
 
  def rtrim!(chars)
    gsub!(/(#{trim_prepare(chars)})+$/, '')
  end
 
  def ltrim!(chars)
    gsub!(/^(#{trim_prepare(chars)})+/, '')
  end
 
  def trim(chars)
    dup.rtrim(chars).ltrim(chars)
  end
 
  def rtrim(chars)
    dup.rtrim!(chars)
  end
 
  def ltrim(chars)
    dup.ltrim!(chars)
  end
 
  private
    def trim_prepare(chars)
      chars = chars.split("").collect { |char| Regexp.escape(char) }
      chars.join('|')
    end
end