Reputation: 33

RegEx for excluding repeating single characters

I'm trying to create a regex that matches a repeating pattern or two or more characters (excluding a single repeating character) three or more times.

(.)\1{3,} will match a single repeated character e.g. matches aaaa but not ababab or abcde

(.+)\1{3,} will match a repeated patern e.g. aaa, ababab, ab ab ab but not abcde

I want to match only ababab, ab ab ab etc but not aaaa or abcde

How do I solve this problem?

Upvotes: 3

Answers (3)

Pushpesh Kumar Rajwanshi

Reputation: 18357

As you want to discard matching if all the characters are same, you can use negative lookahead for rejecting that. In otherwise case, you can change + to {2,} in the quantifier where you are capturing the first part and then use {2,} so your matched first part repeats three or more times. You can use this regex,

^(?!(.)\1+$)(.{2,})\2{2,}$

Explanation:

^ - Start of string
(?!(.)\1+$) - This negative look ahead ensures if the string consists of only one character till end of string, then it rejects the match.
(.{2,}) - Match two or more any character and capture it in group2
\2{2,} - Repeat what was captured in group2 two or more times
$ - End of string

Regex Demo 1

Also, from your post, as you said you don't want to match aaaa since it has aa pattern repeated only two times and not three or more times, so if I am correct and you consider aaaaaa as a successful match, because now it has aa repeating three times, in that case you can get rid of negative lookahead from my above regex and use this regex which will not match aaaa but will match aaaaaa like I explained above.

^(.{2,})\1{2,}$

Regex Demo 2

Let me know if this is indeed what you wanted. In case of any queries, feel free to drop your comment.

Upvotes: 2

Sweeper

Reputation: 274520

You can use this regex:

^((.)\2*?(?!\2).+?)\1{2,}$

The first part ((.)\2*?(?!\2).+?) matches a string that has at least 2 different characters in it, then it repeats it at least 2 more times \1{2,}.

Breaking the first part down, we first match the first character, put it in group 2. Then we allow this character to repeat a few times, or not (\2*). Then we assert that there must be something else other than this character (?!\2). And then we lazily match the rest .+?.