Javascript regex to match a string that ends with some characters but not with a particular combination of those

Question

Let's say using Javascript, I want to match a string that ends with [abcde]* but not with abc.

So the regex should match xxxa, xxxbc, xxxabd but not xxxabc.

I am utterly confused.

Edit: I have to use regex for some reason, i cannot do something if (str.endsWith("abc"))

Answer 1

The solution is simple: use negative lookahead:

(?!.*abc$)

This asserts that the string doesn't end with abc.

You mentioned that you also need the string to end with [abcde]*, but the * means that it's optional, so xxx matches. I assume you really want [abcde]+, which also simply means that it needs to end with [abcde]. In that case, the assertions are:

(?=.*[abcde]$)(?!.*abc$)

See regular-expressions.info for tutorials on positive and negative lookarounds.

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I was reluctant to give the actual Javascript regex since I'm not familiar with the language (though I was confident that the assertions, if supported, would work -- according to regular-expressions.info, Javascript supports positive and negative lookahead). Thanks to Pointy and Alan Moore's comments, I think the proper Javascript regex is this:

var regex = /^(?!.*abc$).*[abcde]$/;

Note that this version (with credit to Alan Moore) no longer needs the positive lookahead. It simply matches .*[abcde]$, but first asserting ^(?!.*abc$).