REGEX to check if a number is repeated in a string

user_9698567 0
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I need a regex that check if a number is repeated in a string of 9 char, knowing that the chars could be an indefinite number of dots

Examples

"........." - false - no numbers repeated
"123456789" - false - no numbers repeated
"1.2.3.4.5" - false - no numbers repeated
"1...3...5" - false - no numbers repeated
"112345678" - true - number 1 is repeated
"1......1." - true - number 1 is repeated
"11244.56." - true - number 1 and 4 are repeated
"234.5.6.4" - true - number 4 is repeated

I found this looking around on internet that is close to what i need

\b(?:([1-9])(?![1-9]*\1)){1,9}\b

But I don't know how to make it not consider dots Thanks very much :)

regex-lookarounds regex
2 Answers

You can use

^(?=.{9}$)(?=.*(\d).*\1)(?:\.*\d){1,9}\.*$

Or, if you need to only allow digits from 1 to 9:

^(?=.{9}$)(?=.*([1-9]).*\1)(?:\.*[1-9]){1,9}\.*$

See this regex demo.

Details:

  • ^ - start of string
  • (?=.{9}$) - the string should contain 9 chars
  • (?=.*(\d).*\1) - there must be a repeating digit
  • (?:\.*\d){1,9}\.* - 1 to 9 occurrences of any zero or more dots followed with a digit and then any zero or more dots
  • $ - end of string.
user_38329700

This regexp will allow any characters between the repeated digits:

(\d).*\1

\d matches a digit, () puts it in capture group 1, and the back-reference \1 matches the same digit.

user_14918950
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