Writing a particular regular expression

Question

I'm trying to come up with a regular expression that I would use to scan a list of strings and store the ones I want. I have most of it working properly but a section of it stumps me.
In order to make my problem as clear as possible, I'll assume that I have some strings that look like the following:
<catapult>
<yay>
<griffin>
<goo>
<dog_man>
<ok>
<>
What I would like to do, is to make the entire string a match, as long as it doesn't contain certain characters and certain substrings.
For instance, say, as long as it doesn't contain the characters "y" or "x", and doesn't contain "cat" or "riff", and is not "goo" then it's a good match. So, the first four in my list should not match and the last three should.
What I tried to do, was create a set of just negating the characters and the substrings contained in groups, which I didn't want. It looked something like this:
<(?:[[^yx]&&[^(?:.*cat.*)]&&[^(?:.*riff.*)]&&[^(?:goo)]]*)>
Apparently this did not produce the results I desired. I assume this can be done but I just can't figure out how.
I hope I made sense. Does anyone have any idea what I need to do?

Answer 1

Wow, thanks so much. That's really helpful. No wonder I couldn't get it. I looked over the tutorials so that helped to clear things up a bit.
Actually, sjasja, I would've done something like that but what I mentioned was just a portion of the patterns that I wanted to match, so although I'm inexperienced with complicated regexes, I figured it would be much neater and concise if I could get it to do what I wanted.
There is a slightly longer, but similar, expression that I would like to match but I suspect I might've made a mistake.
What I want is to have examine a line, and group every instance of what I find within '[ ]'. The substring that would match would be be found in between < >. The first part I would like to be a group of characters (or no characters at all) which don't contain cat, CAT, x or y (anywhere in this area). This time though, I would like something else before the end bracket, so I don't know if I should include the '>' like in the original expression you provided, or not. Following it should be 'cat' or CAT' and then '[ ] >'
What I'm trying to get this pattern to match, are strings like these:
<cat [yay]>
< something CAT [this] >
< dog cat [cat3]>
but not like these:
< cat CAT [yay] >
<catch [HI]>
< CAT CAT [ ] >
What I attempted to do was write the regex as
<\\s*(?:(?!cat|CAT)[^xy])*(?:cat|CAT)\\s*\\[(.*)\\]\\s*>
but I think that (?:(?!cat|CAT)[^xy]) might also match up with the trailing characters, which would result in bad matches. Am I mistaken in this?
I'm sure you're all busy people, but a tip in the right direction would be great.
Thanks again.