findstr - Regex - how to match everything except a particular pattern

Question

How do I write a regex to match any string that doesn't meet a particular pattern? I'm faced with a situation where I have to match an (A and ~B) pattern.

Answer 1

You could use a look-ahead assertion:

(?!999)d{3}

This example matches three digits other than 999.

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But if you happen not to have a regular expression implementation with this feature (see Comparison of Regular Expression Flavors), you probably have to build a regular expression with the basic features on your own.

A compatible regular expression with basic syntax only would be:

[0-8]dd|d[0-8]d|dd[0-8]

This does also match any three digits sequence that is not 999.