Exclude a letter in Regex Pattern

Question

I am trying to create a Regex pattern for <String>-<String>. This is my current pattern:

(\w+\-\w+).

The first String is not allowed to be "W". However, it can still contain "W"s if it's more than one letter long.

For example: W-80 -> invalid W42-80 -> valid

How can this be achieved?

Answer 1

Just restrict the last char to "any word char except 'W'".

There are a couple of ways to do this:

Negative look-behind (easy to read):

^\w+(?<!W)-\w+$

See live demo.

Negated intersection (trainwreck to read):

^\w*[\w&&[^W]]-\w+$

See live demo.

——

The question has shifted. Here’s a new take:

^.+(?<!^W)-\w+

This allows anything as the first term except just "W".

Answer 2

So your first string can be either: one character but not W or 2+ characters. Simple pattern to achieve that is:

([^W]|\w{2,})-\w+

But this pattern is not entirely correct, because now it allows any character for first part, but originally only \w characters were expected to be allowed. So correct pattern is:

([\w&&[^W]]|\w{2,})-\w+

Pattern [\w&&[^W]] means any character from \w character class except W character.