Regular Expressions matching difficulty

Question

My current regex:

([\d]*)([^\d]*[\d][a-z]*-[\d]*)([\d][a-z?])(.?)

Right so I am attempting to make regex match a string based on: a count that can be any amount of number from 0-1million then followed by a number then sometimes a letter then - then any number for numbers followed by the same number and sometimes a letter then sometimes a letter. example of strings it should match:

1921-1220104081741b
192123212a-1220234104081742ab

an example of what it should return based on above (this is 2 examples it shouldn't read both lines.)

(192) (1-122010408174) (1) (b)
(19212321) (2a-122023410408174) (2a) (b)

My current regex works with the second one but it returns (1b) in the first when I would like it to return (1) (b) but also return (2a) in the case of the second one or the case of:

1926h-1220104081746h  Should Return: (192) (6h-122010408174) (6h)

Not 100% sure if its possible, sense I'm fairly new to regex. For reference I'm doing this in excel-vba if there is any other way to do this easier.

Answer 1

You could capture the character(s) before the dash character, and then back reference that match.

In the expression below, \3 would match what was matched by the 3rd capturing group:

(\d*)((\d[a-z]*)-\d*)(\3)([a-z])?

Example Here

Output after merging the capture groups:

1921-1220104081741b
(192) (1-122010408174) (1) (b)

192123212a-1220234104081742ab
(19212321) (2a-122023410408174) (2a) (b)

1926h-1220104081746h
(192) (6h-122010408174) (6h)

Example:

Disregard the JS. Here is the output after merging the capture groups:

var strings = ['1921-1220104081741b', '192123212a-1220234104081742ab', '1926h-1220104081746h'], exp = /(\d*)((\d[a-z]*)-\d*)(\3)([a-z])?/;

strings.forEach(function(str) {
  var m = str.match(exp);
  
  snippet.log(str);
  snippet.log('(' + m[1] + ') ('+ m[2] + ') (' + m[4] + ') (' + (m[5]||'') + ')');
  snippet.log('---');
});

<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

Answer 2

I think what you are saying with "followed by the same number" is that the piece right before the dash is repeated as your third capture group. I would suggest implementing this by splitting up your second capture group and then using a backreference:

([\d]*)([\d][a-z]*)-([\d]*)(\2)(.?)

For your three examples:

1921-1220104081741b
192123212a-1220234104081742ab
1926h-1220104081746h

This results in:

(192)      (1)  - (122010408174)    (1)  (b)
(19212321) (2a) - (122023410408174) (2a) (b)
(192)      (6h) - (122010408174)    (6h) ()

...and you can join the two middle groups back together to get the hyphenated term you wanted.