Regex to find repeating numbers

Question

Can anyone help me or direct me to build a regex to validate repeating numbers

eg : 11111111, 2222, 99999999999, etc

It should validate for any length.

Answer 1

(d)1+

Explanation:

   # match word boundary
(d) # match digit remember it
1+  # match one or more instances of the previously matched digit
   # match word boundary

If 1 should also be a valid match (zero repetitions), use a * instead of the +.

If you also want to allow longer repeats (123123123) use

(d+)1+

If the regex should be applied to the entire string (as opposed to finding "repeat-numbers in a longer string), use start- and end-of-line anchors instead of :

^(d)1+$

Edit: How to match the exact opposite, i. e. a number where not all digits are the same (except if the entire number is simply a digit):

^(d)(?!1+$)d*$

^     # Start of string
(d)  # Match a digit
(?!   # Assert that the following doesn't match:
 1+  # one or more repetitions of the previously matched digit
 $    # until the end of the string
)     # End of lookahead assertion
d*   # Match zero or more digits
$     # until the end of the string