Question

So my forum allows me to use a regex to allow certain user names registration, but I want to do that opposite and block any non-matches, which the system doesn’t allow for inherently.

How can I not match a pattern of [a-zA-Z]+[0-9]{4}?

Meaning that it would return false for, say

FOobar1234
bar5678

I’ve tried but can’t get this to work.

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Sort of how like [^a-zA-Z]+ would return false for foobar (matches a-z) but with 4 digits at the end too.

Answer 1

You can make use of negative lookahead assertion:

^(?![a-zA-Z]+[0-9]{4}$)

In general:

^(?!<pattern>$)

matches only those strings that do not match the regex <pattern>.

See it