Question

I need a regex that allows numbers and optional commas, but the entire length cannot be greater than 6.

^[0-9]+([,]*[0-9]+)*$ allows numbers and optional commas.

^([0-9]+([,]*[0-9]+)*){0,6}$ does not limit the total length to 6.

Answer 1

If your regex engine supports lookahead assertions — most do — then you can write:

^(?=[0-9,]{1,6}$)[0-9]+(,[0-9]+)*$

The (?=[0-9,]{1,6}$) part is a “positive lookahead assertion”, and means “looking forward from this point in the string, I see [0-9,]{1,6}$“. So, in essence, the above regex is a combination of these two:

^[0-9,]{1,6}$
^[0-9]+(,[0-9]+)*$

and enforces them both.

(That said, it’s likely to be clearer if you simply enforce the length restriction as a separate step, rather than incorporating the above into a single regex.)