Question

can you help me with this:

I want a regular expression for my Ruby program to match a word with the below pattern

Pattern has

1. List of letters ( For example. ABCC => 1 A, 1 B, 2 C )
2. N Wild Card Charaters ( N can be 0 or 1 or 2)
3. A fixed word (for example “XY”).

Rules:

1. Regarding the List of letters, it should match words with

   a. 0 or 1 A

   b. 0 or 1 B

   c. 0 or 1 or 2 C

2. Based on the value of N, there can be 0 or 1 or 2 wild chars
3. Fixed word is always in the order it is given.
4. The combination of all these can be in any order and should match words like below

ABWXY ( if wild char = 1)

BAXY

CXYCB

But not words with 2 A’s or 2 B’s

I am using the pattern like ^[ABCC]*.XY$

But it looks for words with more than 1 A, or 1 B or 2 C’s and also looks for words which end with XY, I want all words which have XY in any place and letters and wild chars in any postion.

Answer 1

I consider myself to be fairly good with regular expressions and I can’t think of a way to do what you’re asking. Regular expressions look for patterns and what you seem to want is quite a few different patterns. It might be more appropriate to in your case to write a function which splits the string into characters and count what you have so you can satisfy your criteria.

Just to give an example of your problem, a regex like /[abc]/ will match every single occurrence of a, b and c regardless of how many times those letters appear in the string. You can try /c{1,2}/ and it will match “c”, “cc”, and “ccc”. It matches the last case because you have a pattern of 1 c and 2 c’s in “ccc”.

One thing I have found invaluable when developing and debugging regular expressions is rubular.com. Try some examples and I think you’ll see what you’re up against.

I don’t know if this is really any help but it might help you choose a direction.