match the same unknown character multiple times

Question

I have a regex problem I can't seem to solve. I actually don't know if regex can do this, but I need to match a range of characters n times at the end of a pattern. eg. blahblah[A-Z]{n} The problem is whatever character matches the ending range need to be all the same.

For example, I want to match

• blahblahAAAAA
• blahblahEEEEE
• blahblahQQQQQ

but not

• blahblahADFES
• blahblahZYYYY

Is there some regex pattern that can do this?

Answer 1

You can use this pattern: blahblah([A-Z])\1+

The \1 is a back-reference to the first capture group, in this case ([A-Z]). And the + will match that character one or more times. To limit it you can replace the + with a specific number of repetitions using {n}, such as \1{3} which will match it three times.

If you need the entire string to match then be sure to prefix with ^ and end with $, respectively, so that the pattern becomes ^blahblah([A-Z])\1+$

You can read more about back-references here.

Answer 2

In most regex implementations, you can accomplish this by referencing a capture group in your regex. For your example, you can use the following to match the same uppercase character five times:

blahblah([A-Z])\1{4}

Note that to match the regex n times, you need to use \1{n-1} since one match will come from the capture group.