How do I negate an exact match in regex?

Question

If the user enters exactly "null", I want the regex match to fail. Entering "xxxnullxxx" is ok however.

The following regex rejects "null" but it also rejects any string containing "null", which I don't want.

^(?!.*null).*$

Possible duplicate of [How to negate the whole regex?](http://stackoverflow.com/questions/2637675/how-to-negate-the-whole-regex) — Martin Cup, Dec 01 '16 at 00:27
@4castle there are plenty of cases where the validation API is regex (only) — Bohemian, Dec 01 '16 at 02:30
@4castle: I'm using a JavaScript library which accepts regex to validate form fields. — Jin Kim, Dec 01 '16 at 06:27

score 3 · Answer 1 · answered Dec 01 '16 at 02:28

3

Add $ and remove .* from the look ahead:

^(?!null$).*

The trailing $ isn't needed.

answered Dec 01 '16 at 02:28

Bohemian

1

I was able to get it working after using a variation of your answer:. ^(?!null$) without the trailing .$. – Jin Kim Dec 01 '16 at 06:43
@jim if you mean `^(?!null).*`, that would match `"nullify"` etc – Bohemian Dec 01 '16 at 17:03
2

I meant `^(?!null$)`. I only want to ignore the exact match "null". – Jin Kim Dec 01 '16 at 20:58

score 1 · Answer 2 · edited May 23 '17 at 12:08

1

This will match everything except for null: ^(?!(?:null)$).*$ I got the idea from here.

edited May 23 '17 at 12:08

Community

answered Dec 01 '16 at 00:25

Martin Cup

2 Answers2