Regular expression for avoid repeated consecutive chars, but excluding one specific char

user_5763993 0
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I am learning a lot of Regex with Python, and I am struggled with a regex for allow test cases where doesn't have consecutive 4 or more repeated chars, I have found easy solutions in Internet but I need evaluate the repeated chars excluding the "-" char, for example:

bic-hota  // Valid
bichota  // Valid
bichota1234 // Valid
bich222ota // Valid, sequence "222" with length of 3 is allowed 

bichota2222 // Invalid because have "2222" and isn't allowed length of 4 or more
bichota22-22 // Invalid because have "2222" (ignore the '-') and isn't allowed length of 4 or more

In the last test case, you can see the sequence "22-22", I need ignore the "-" between the sequence for validate whole the sequence, and I have searched about how to solve this and I have use the Non-capture group (?:-?) but this doesn't works :(

^(?![\w]*([\w])(?:-?)\1{3,})[\w-]+$

What is wrong with my regex and how to fix it?

Test cases: https://regexr.com/6p0ca

regex-negation regex-group python-3.x regex
2 Answers

You may use this regex:

^(?!.*(\w)(?:-?\1){3}).+

RegEx Demo

RegEx Details:

  • ^: Start
  • (?!: Start negative lookahead
    • .*: Match any length of characters
    • (\w): Match a character and capture in group #1
    • (?:-?\1){3}: Match optional - followed by back-reference to group #1. Repeat this group 3 times.
  • ): End negative lookahead
  • .+: Match 1+ of any characters

To allow only word characters and hyphens use:

^(?![\w-]*(\w)(?:-?\1){3})[\w-]+$
user_5482250

Or match the unwanted:

[^\w-]|(\w)(-?\1){3}
  • [^\w-] a character that is not a word character or hyphen
  • (\w)(-?\1){3} four repeated \w with optional hyphen in between
  • |^$ can be further attached for empty string positives if needed (demo)

See this demo at regex101 (the \n is just used for the multiline demo)

This way the matched part could even be displayed in some fail-message.

user_55279850
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