Regular Expression problem: how to determine that there's no B between A and C?

Question

Hi!

I need an regular expression that matches A.*C only if there's no "B" in between. Before and after "A.*C without B in between", any string is allowed (including A, B and C).
"A", "B" and "C" are placeholders for longer strings.
So the regex should match ie. "AfooC", "AfooCbarB", "A C B A", but not "AfooBbarC" or "A B C B".

I think I need a .* somewhere between A and B, so I tried (amongst others) these two:
A.*(?!B).*C doesn't work, as the .* after A "eats" the B.
A(?!.*B).*C doesn't work, as it doesn't match ACB. (This time, the first .* "eats" the "C").

Possibly I'm missing something obvious - I can't figure out how to do it.

Thanks for the help, Julian

(Edit: having some formatting troubles...)

Answer 1

The easiest way to achieve this is using lookarounds:

A((?!B).)*C

This pattern will match A, then any number of characters, and then C. However, because of the negative lookahead on the ., the dot will only match if it isn't going to consume B.

Answer 2

How about A[^B]*C? [^B] is a character class matching "anything but the letter 'B'".

Answer 3

"A[^B]*C". Matches an A, then any number of characters that isn't B, then C.

Answer 4

Why not /A(?!.*B.*(C)).*?C/ ?

Answer 5

How about this:

\AA.+(?<!(.*cheesey.*))C\Z

The (?<!(.*cheesey.*)) does a negative lookbehind for the pattern .*cheesey.* and stops matching if it finds a match. The anchors are there to stop it from chopping off the end and matching in the middle even though 'cheesey' might be at the end.