Matching pattern using regular expression

Question

I have to match sequence like baab, sdds in the string and the sequence should not be inside the square brackets. So far i have used the regular expression

/([a-z])([a-z])\2{1}\1{1}(?![^[]*])/

It is giving me the desired output but the above regular expression also matching the sequence like bbbb which is undesirable. I am thinking of having something to compare capture group1 and capture group2 not be equal.So far i didn't find anything useful.

Link for same

(i.e., you can use negative lookahead to ensure the two groups are not equal) — user202729, Jan 21 '18 at 13:12
Looks like you already know about negative lookahead, why can't you do this? — user202729, Jan 21 '18 at 13:12
@user202729 No, it's not a duplicate, OP wants what the fourth bird suggested (looks like matching four-character palindromes except ones composed of four identical characters). — Sergey Kalinichenko, Jan 21 '18 at 13:16
Please note that it would be better if you specify the language you're using. There is no standard for regular expressions and specifying the language is a way to attract the best answers — Andrea Corbellini, Jan 21 '18 at 13:29
I am not using any specific language but using https://regexr.com/ to fiddle around, how php would be a choice — ashofphoenix, Jan 21 '18 at 14:53

The fourth bird · Accepted Answer · 2018-01-21T13:25:34.233

2

I think you could add a negative lookahead after group 1 (?!\1) to assert that what follows the first group is not the same as group 1.

([a-z])(?!\1)([a-z])\2\1(?![^[]*])

If you don't want your match to be between square brackets, you could add a negative lookbehind (?<!\[)([a-z])(?!\1)([a-z])\2\1(?!]) to assert that your match does not start with [. (if your engine supports this).

edited Jan 21 '18 at 13:25

answered Jan 21 '18 at 13:13

The fourth bird

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the regex given in line 1 is does ignoring the match if inside square brackets. I was wondering if it is possible to ignore the match found in line if there also exist a match between square brackets – ashofphoenix Jan 21 '18 at 14:31
@ashofphoenix Not really sure what you mean, could you give an example? – The fourth bird Jan 21 '18 at 14:52
Yes as you can see that in test input line 2 has the match inside as well as the outside of brackets https://regex101.com/r/Jqw6Pm/4 once i remove the pattern to ignore square brackets – ashofphoenix Jan 21 '18 at 14:58
@ashofphoenix For this scenario with new requirements, you could consider creating a new question with a detailed example and if possible the programming language. – The fourth bird Jan 21 '18 at 15:45

Matching pattern using regular expression

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