Ruby regex remove ^C character from string - ruby

Question

There is a file that has control B and control C commands separating fields of text. It looks like:
"TEST\003KEY\002TEST\003KEY"
I tried to create a regex that will match this and remove it. I am not sure why this regex is not working:
"TEST\003KEY\002TEST\003KEY".gsub(/\00[23]/, ',')

Answer 1

Try the following:
"TEST\003KEY\002TEST\003KEY".gsub(/\002|\003/, ',')
Here it is demonstrated in irb on my machine:
$ irb
1.9.3p448 :007 > "TEST\003KEY\002TEST\003KEY".gsub(/\002|\003/, ',')
=> "TEST,KEY,TEST,KEY"
The syntax \002|\003 means "match the character literal \002 or the character literal \003". The expression given in the original question \00[23] is not valid: this is the character literal \00 (a null character) followed by the character class [23]: i.e. it matches two-character sequences.
You can also use the [[:cntrl:]] character class to match all control characters:
$ irb
1.9.3p448 :007 > "TEST\003KEY\002TEST\003KEY\005TEST".gsub(/[[:cntrl:]]/, ',')
=> "TEST,KEY,TEST,KEY,TEST"

Answer 2

Here's the deal. First and foremost, computers cannot store characters--they can only store numbers. So when a computer stores a string it converts every character to a number. The numbers for all the basic characters are given by an ascii chart(you can search google for one).
When you tell a computer to print a string, it retrieves the numbers saved for the string and outputs them as characters (using an ascii chart to convert the numbers to characters).
Double quoted strings can contain what are called escape sequences. The most common escape sequence is "\n":
puts "hello\nworld"
--output:--
hello
world
A double quoted string converts the escape sequence "\n" to the ascii code 10:
puts "\n".ord #=>10 (ord() will show you the ascii code for a character)
A double quoted string can also contain escape sequences of the form \ddd, e.g. \002. Escape sequences like that are called octal escape sequences, which means 002 is the octal representation of an ascii code.
In an octal number, the right most digit is the 1's column, and the next digit to the left is the 8's column and the next digit to the left is the 64's column. For instance, this octal number:
\123
is equivalent to 3*1 + 2*8 + 1*64 = 83. It so happens that an "S" has the ascii code 83:
puts "\123" #=>S
Because you also can use octal escape sequences in a double quoted string, that means that instead of using the escape sequence "\n" you could use the octal escape "\012" (2*1 + 1*8 + 0*64 = 10). A double quoted string converts the octal escape sequence "\012" to the ascii code 10, which is the same thing that a double quoted string does to "\n". Here is an example:
puts "hello" + "\012" + "world"
--output:--
hello
world
The final thing to note about octal escape sequences is that you can optionally leave off any leading 0's:
puts "hello" + "\12" + "world"
--output:--
hello
world
Okay, now examine your string:
"TEST\003KEY\002TEST\003KEY"
You can see that it contains three octal escape sequences. A double quoted string converts the octal escape sequence \003 to the ascii code: 3*1 + 0*8 + 0*64 = 3. If you check an ascii chart, the ascii code 3 represents a character called "end of text". A double quoted string converts the octal escape sequence \002 to the ascii code: 2*1 + 0*8 + 0*64 = 2, which represents a character called 'start of text'. I'm not sure where you are getting the "control B" and "control C" names from (maybe those are the key strokes on your keyboard that are mapped to those characters?).
Next, a regex acts like a double quoted string, so
/<in here>/
you can use the same escape sequences as in a double quoted string, and the regex will convert the escape sequences to ascii codes.
Now, in light of all the above, examine your regex:
/\00[23]/
As Richard Cook pointed out, your regex gets interpreted as the octal escape sequence \00 followed by the character class [23]. The octal escape sequence \00 gets converted to the ascii code: 0*1 + 0*8 = 0. And if you look at an ascii chart, the number 0 represents a character called 'null'. So your regex is looking for a null character, followed by either a "2" or a "3", which means your regex is looking for a two character string. But a two character string will never match the octal escape sequence "\003" (or "\002"), which represents only one character.
The main thing to take away from all this is that when you see a string that contains an octal escape sequence:
"hello\012world"
...that string does not contain the characters \, 0, 1, and 2. A double quoted string converts that sequence of characters into one ascii code, which represents ONE character. You can prove that very easily:
puts "hello".length #=>5
puts "hello\012".length #=>6
There are also many other types of escape sequences that can appear in double quoted strings. You would think they would be listed in the String class docs, but they are not.

Answer 3

s = "TEST\003KEY\002TEST\003KEY"
s.split(/[[:cntrl:]]/) * ","
# => "TEST,KEY,TEST,KEY"