Negate match in RE2 syntax?

Question

How can I write a regex in RE2 for "match strings not starting with 4 or 5"?

In PCRE I'd use ^(?!4) but RE2 doesn't support that syntax.

You can use `^[^45]` but it will consume a character. – Lucas Trzesniewski Jan 28 '15 at 16:24 — Lucas Trzesniewski, Jan 28 '15 at 16:24

score 9 · Accepted Answer · answered Jan 28 '15 at 16:24

9

You can use this regex:

^[^45]

^ matches start and [^45] matches anything but 4 or 5 at start.

answered Jan 28 '15 at 16:24

anubhava

2

And if you also want to match the empty string, use `^(?:[^45]|$)`. – Tim Pietzcker Jan 28 '15 at 16:28
1

Yes that's right, thanks for adding this important addendum @TimPietzcker – anubhava Jan 28 '15 at 16:30
similar to this how to omit the word when it contains `-ed` in it? any idea for this [link](https://regex101.com/r/I5Wsbf/3). Here 2 match cases are working fine, but condition on negate (not matching case) seems to be not working. Pls correct me if i'm wrong. @anubhava – CdVr Jul 25 '20 at 07:31

score 0 · Answer 2 · edited May 26 '23 at 13:19

Here's a variant of the solution for strings of words, not individual characters.

The way I do it is to look twice.

First, find all the items that match, then filter them to get the final answer

example

use re2 I will choose divide and conquer: To a reduced scope with the group, and then filter.

a solution writing with Golang =>