Regular Expressions matching difficulty - regex

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.