RegEx to check 3 or more consecutive occurrences of a character

Question

I want to check an input string to validate a proper text.

a. I want the users to allow to writer alphanumeric characters including period, comma, hyphen and round b

Answer 1

You can use the regex:

(?!.*(.)\1{2})^[a-zA-Z0-9.,()-]*$

It uses the negative lookahead (?!.*(.)\1{2}) to ensure that there is no group of 3 repetitions of any of the characters.

Then it uses the regex ^[a-zA-Z0-9.,()-]*$ to ensure that the string is made of just alphabets, numbers, period, comma, parenthesis and hyphen.

Rubular link

Answer 2

Most regex libs support the folloing: /(.)\1{2,}/

where \1 is a a backreference