Regex at the beginning of a string in context

Question

I've got the following RegEx-Pattern:

pattern = @"(?<=\[)[\da-f]{8}(?=\])";

It extracts " f000000f " out of " [f000000f] Bar " correctly, but it should not match on " Foo [f000000f] Bar " so i've added the ^ to determine the beginning of the pattern:

pattern = @"^(?<=\[)[\da-f]{8}(?=\])";

But this pattern doesn't work for both inputs.

Can anybody tell me how to force the first pattern to match only at the beginning of the input-String?

Thanks in advance.

Answer 1

You need to move the anchor inside the lookbehind, like this:

(?<=^[)[\da-f]{8}(?=])"

Otherwise, you wouldn't match [f000000f] , because no part of your expression "consumes" the opening square bracket [ .