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Asked: 2026-05-23T00:33:01+00:00

I’m looking to apply a regular expression to an input string to make sure

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I’m looking to apply a regular expression to an input string to make sure it doesn’t match a list of predefined values. For example, if I pass in the word Dog, I don’t want it to match. Likewise for Cat. However, if I pass in Sheep, it should match.
I’ve tried:

^(?!(Dog)|(Cat))$ << Doesn’t match Dog, Cat or sheep!
^((?!Dog)|(?!Cat))$ << Doesn’t match Dog, Cat or sheep!
^(?!Dog|Cat)$ << Doesn’t match Dog, Cat or sheep!
^(?!Dog)|(?!Cat)$ << matches everything because Dog != Cat for example

Basically, if I pass in “Dogs”, it should match as dog != dogs. But if I pass in exactly dog or cat then it should not match.

I thought this would be really easy, but I’m puling my hair out!
Thanks

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1 Answer

  1. Editorial Team

    The lookahead assertions doesn’t match anything. after closing it you need to match the characters, so try e.g.

    ^(?!.*Dog)(?!.*cat).*$

    See it here at Regexr

    They are described here in detail on msdn

    If you want to match those words exactly then use word boundaries like this

    ^(?!.*\bDog\b)(?!.*\bCat\b).*$

    Regexr

    The \b ensures that there is no word character before or following

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