Ruby unfamiliar string usage with Integer.chr and "\001" - ruby

Question

Recently I stumbled over this code snippet in Ruby:
#data = 3.chr * 5
which results in "\003\003\003\003\003"
later in the code for example
flag = #data[2] & 2
is used,
I know that it has something todo with bitwise-flags. It seems the values 1,2 and 3 are used as state flags, but because ruby 1.9, which is the version I am familar with, changed the Integer.chr method the code does no longer work and I would really like to know whats going on.
Furthermore, what is the purpose of the "\00x" escaped-thing?
Thanks for your answers

Answer 1

To make the code work in Ruby 1.9, try changing that line to:
flag = #data[2].ord & 2
Prior to Ruby 1.9, str[n] would return an integer between 0 and 255, but in Ruby 1.9 with its new unicode support, str[n] returns a character (string of length 1). To get the integer instead of character, you can call .ord on the character.
The & operator is just the standard bitwise AND operator common to C, Ruby, and many other languages.
Byte number three (0x03) is not a printable ASCII character, so when you have that byte in a string and call inspect ruby denotes that byte as \003. Just make sure you understand that "\003" is a single-byte string while '\003' is a four-byte string.
In Ruby, strings are really sequences of bytes. In Ruby 1.9, there is also encoding information, but they are still really just a sequence of bytes.

Answer 2

The "\00X" thing is an octal representation of the value.
So if we do:
irb(main):001:0> 15.chr
=> "\017"
irb(main):002:0> 16.chr
=> "\020"
Notice how we went from 17 right to 20? Octal.
"\003\003\003\003\003" is 5 bytes of the value 3 and you can then bitwise and them with other bytes, such as 2 or \002.
So 3 or 0011 in binary anded with 2 (0010) is 2 (0010)
The 1.9 issue occurs on account of 1.9 not using ascii like 1.8 does. David Grayson hits that point well.

Answer 3

Note that ruby 1.9 will inspect unprintable characters in the hexadecimal representation:
3.chr # => "\x03"
Even more confusing is that sometimes the strings will appear in unicode (UTF-8):
"\003" # => "\u0003" (utf-8)
3.chr.encoding # => #<Encoding:US-ASCII>
"\003".encoding # => #<Encoding:UTF-8>
"\003" == 3.chr # => true (this is strange because the encoding is different)
If you're trying to understand how these octal and hex strings relate to decimal numbers, you can convert them to binary:
"\003".unpack('B*') # same as "\003".ord.to_s(2)
# => ["00000011"] # the 2 least significant bits are set
2.to_s(2) # convert to base 2
#=> "10"
The expression 3 & 2 is a bitwise-and of binary numbers 11b and 10b, which will yield 10b (because 1 & 1 is 1 for the most significant bit; 1 & 0 is 0 for least significant).
Other conversions:
'%x' % 97 # => '61' hex
0x61 # => 97 decimal from raw hex input
'%o' % 97 # => '141' octal
0141 # => 97 decimal from raw octal input
This is sort of a crash course but you should probably google for more in-depth info.