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

\b(\d)\1+\b 

Explanation:

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

\b(\d+)\1+\b 

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 \b:

^(\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 

Answer 2

To match a number of repetitions of a single digit, you can write ([0-9])\1*.

This matches [0-9] into a group, then matches 0 or more repetions (\1) of that group.

You can write \1+ to match one or more repetitions.