Convert hex string to ruby string

conv_hexstr.rb

#!/usr/bin/env ruby

def convert_hexstr(str, start=0, index=nil)
  index ||= str.length
  hexstr = str[start, index]
  ar = []
  hexstr.scan(/\\x../).each do |s|
    ar << s.gsub('\\', '0').to_i(16)
  end
  ar.empty? ? str : ar.pack('C*').force_encoding('utf-8')
end

def convert(str)
  non_hexstr_start += 4 if
    non_hexstr_start = str.index(/(\\x..)([^(\\x..)]+)(\\x..)/)
  hexstr_start, hexstr_end = str.index(/\\x../), str.rindex(/\\x../)

  if ! non_hexstr_start
    if hexstr_start || hexstr_end
      hexstr_length = hexstr_end + 3 - hexstr_start + 1
      str[hexstr_start, hexstr_length] = convert_hexstr(str)
    end
    str
  else
    hexstr_length = non_hexstr_start - hexstr_start
    parsed_str_before_non_hexstr = convert_hexstr(str, hexstr_start,
                                                  hexstr_length)
    str[hexstr_start, hexstr_length] = parsed_str_before_non_hexstr

    convert(str)
  end
end

def main
  f_name = ARGV[0]
  new_lines = Array.new
  File.open(f_name) do |f|
    f.each do |line|
      new_lines << convert(line)
    end
  end
  File.open(f_name, 'w') { |f| f.write new_lines.join }
end

def test
  puts convert('\xE7\x94\xA8 Python \xE5\xBB\xBA\xE8\x8B\xB1\xE8\xAF\xAD\xE5\x8D\x95\xE8\xAF\x8D\xE8\xA1\xA8')
  puts convert('\xE8\xAE\xA9\xE4\xBD\xA0\xE7\x9A\x84MSN\xE5\x89\x8D\xE9\x9D\xA2\xE5\xA4\x9A\xE4\xB8\xAAIAM\xE7\x9A\x84\xE6\x96\xB9\xE6\xB3\x95[\xE8\xBD\xAC]')
  puts convert('Wordpress on dotcloud')
  puts convert('Eng\xE7\x94\xA8lish')
end

#test
main