Question

I have some strings that I would like to pattern match and then extract out the matches as variables $1, $2, etc.

The pattern matching code I have is

a = /^([\+|\-]?[1-9]?)([C|P])(?:([\+|\-][1-9]?)([C|P]))*$/i.match(field)

puts result = #{a.to_a.inspect}

With the above I am able to easily match the following sample strings:

“C”, “+2C”, “2c-P”, “2C-3P”, “P+C”

And I have confirmed all of these work on the Rubular website.
However, when I try to match “+2P-c-3p”, it matches however, the MatchData “array-like object” looks like this:

result = ["+2P-C-3P", "+2", "P", "-3", "P"]

The problem is that I am unable to extract into the array, the middle pattern “-C”.

What I would expect to see is:

result = ["+2P-C-3P", "+2", "P", "-", "C", "-3", "P"]

It seems to extract only the end part “-3P” as “-3” and “P”

Does anyone know how I can modify my pattern to capture the middle matches ?
So as an other example, +3c+2p-c-4p, I would expect should create:

["+3c+2p-c-4p", "+3", "C", "+2", "P", "-", "C", "-4", "P"]

but what I get is

["+3c+2p-c-4p", "+3", "C", "-4", "P"]

which completely misses the middle part.

Answer 1

This is what I managed to do :

([+-]?\d?)(C|P)(?=(?:[+-]?\d?[CP])*$)

This way you capture multiple elements.
The only problem is the validity of the string. As ruby doesn’t have look-behind I can’t check the start of the string, so zerhyju+2P-C-3P is valid (but will only capture +2P-C-3P) whereas +2P-C-3Pzertyuio isn’t valid.

If you want to both capture and check if your string is valid, the best way (IMO) is to use two regexes, one to check the value ^(?:[+-]?\d?[CP])*$ and a second one to capture ([+-]?\d?)(C|P) (You could also use ([CP]) for the last part).