Regular expression, is this possible?

Question

So far I have:

^[1-6],[1-6]$

The above will permit a comma delimited expression of two numbers where each number must be between 1 and 6.

Is it possible to include a comparison in the expression which would mean that the first number must be exactly 1 less than the second number and that the first number and second numbers must be different?

No. Since from Regex's point of view, it is dealing with a string not a number. — Ali Samji, May 10 '21 at 18:07
@WiktorStribiżew, ok, slight variant, how would I modify the expression to allow optional multiples of the same following the same rules, e.g. 1,2,3,4 or 4,5,6 ? — SPlatten, May 10 '21 at 18:15
i think @anubhava could set its comment as answer ( [demo](https://regex101.com/r/9Byh6L/1) ) — SL5net, May 10 '21 at 18:52
No, regular expressions do not do mathematical calculations. — Andy Lester, May 10 '21 at 22:10
@SPlatten "?:" is not required, and it is not "best practice". It tells the engine to not save that grouping in a variable that you can use later. Using "?:" will save you milliseconds, but if you don't care about that, then don't clutter up your code. — Andy Lester, May 10 '21 at 22:11

score 0 · Accepted Answer · answered May 10 '21 at 21:17

The top comments are correct: there is no way other than "brute force" or "spelling out" alternatives as there is no way to do math inside a regular expression.

Use any version, with capturing or non-capturing groups:

^(?:1,2|2,3|3,4|4,5|5,6)$
^(1,2|2,3|3,4|4,5|5,6)$

See regex proof.

EXPLANATION

--------------------------------------------------------------------------------
  ^                        the beginning of the string
--------------------------------------------------------------------------------
  (?:                      group, but do not capture:
--------------------------------------------------------------------------------
    1,2                      '1,2'
--------------------------------------------------------------------------------
   |                        OR
--------------------------------------------------------------------------------
    2,3                      '2,3'
--------------------------------------------------------------------------------
   |                        OR
--------------------------------------------------------------------------------
    3,4                      '3,4'
--------------------------------------------------------------------------------
   |                        OR
--------------------------------------------------------------------------------
    4,5                      '4,5'
--------------------------------------------------------------------------------
   |                        OR
--------------------------------------------------------------------------------
    5,6                      '5,6'
--------------------------------------------------------------------------------
  )                        end of grouping
--------------------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string

Regular expression, is this possible?

1 Answers1