How do i write a Regular Expression to match text containing XYZ but not ABC?

Question

I want to write a regex that matches if a string contains XYZ but doesn't contain ABC somewhere before it. So "blah XYZ blah" should match, but "blah ABC blah XYZ blah " should not.

Any ideas? In particular I'm writing the regex in c#, in case there's anything specific to that syntax.

I guess I can use negative lookbehind but haven't used this before...

thanks!

UPDATE: I need a regex as I don't have the ability to modify the code, just some configuration.

UPDATE: Changed as I actually only need to check that ABC doesn't appear before XYZ, I don't need to check if it comes after.

Answer 1

is there anything wrong with

 string.Contains("XYZ") && !string.contains("ABC")

Answer 2

Get Expresso. My opinion is that regex's are difficult to master and you'll want to test them thoroughly anyway, so having a tool that helps you with both is the best bet. It's pretty easy to use, there's tutorials out there for it.

Best thing about it: it will generate a chunk of C# code that has your regex in it.

Answer 3

Are you sure this is a regular expression?

Answer 4

that should do the trick:

^([^(ABC)]*)(XYZ)(.*)$

some examples:

sadsafjaspodsa //False
sadABCdsaABCdsa //False
sadABCdsaABCdsaXYZ //False
sadABCdsaABCdsaXYZaa //False
sadABCddasABCsaXYZdsa //False
sadsaXYZdsa //True
sadsaXYZ //True

Answer 5

^(?:(?<!ABC).)*XYZ

was fine for my little testset.

Answer 6

This should work:

^(?:(?!ABC).{3,})?XYZ

And if it also should not appear after XYZ:

^(?:(?!ABC).{3,})?XYZ(?:.{3,}(?<!ABC))?$

Answer 7

No need for lookbehind:

^(?:(?!ABC).)*XYZ