ansaurus

Question

Regular Expression Word Boundary and Special Characters

Answer 1

A:

Try changing it to:

/\b\s?+/gi

Edit:

Extend this concept as far as you want. If you want the first + after any word boundary:

/\b[^+]*+/gi

Stargazer712 2010-07-13 21:31:18

That works in the specific example I gave, but doesn't account for word boundaries properly. For example, it doesn't work on 'add (+)' as the haystack.

dosboy 2010-07-13 21:35:15

I edited my answer to account for a more general case, but if that's not what you're looking for, then you need to be more specific on what you want.

Stargazer712 2010-07-13 21:41:18

Not sure how to be more specific. I need to use the word boundary \b to specify that the special character is at the beginning of a word. I updated the question to include 'add (+)' as an example, but there are obviously dozens more where some character (other than whitespace) designates a word boundary.

dosboy 2010-07-13 21:44:19

Then I'm sorry, but I can't help you figure out what you need.

Stargazer712 2010-07-13 21:48:25

Answer 2

+1 A:

\b is a zero-width assertion: it doesn't consume any characters, it just asserts that a certain condition holds at a given position. A word boundary asserts that the position is either preceded by a word character and not followed by one, or followed by a word character and not preceded by one. (A "word character" is a letter, a digit, or an underscore.) In your string:

add +

...there's a word boundary at the beginning because the a is not preceded by a word character, and there's one after the second d because it's not followed by a word character. The \b in your regex (/\b\+/) is trying to match between the space and the +, which doesn't work because neither of those is a word character.

Alan Moore 2010-07-13 22:01:06

That makes a lot of sense actually. I take it then that there's no way to achieve what I want to without creating a list of pre-defined characters (such as `\s`, `\(`, `\[`, etc.) to match against before the `+`?

dosboy 2010-07-13 22:05:53

Do you want to match anything that's *not* a word character? That would be `\W` (capital 'w'). Or you can use `\B` to assert that the `+` is not preceded by a word character.

Alan Moore 2010-07-13 22:18:13

Definitely not *not* a word character, but your explanation of the actual usage of `\b` gave me a kick in the right direction. I'm now doing a JS check on the first character of my regex. If it's a `\\` I don't append the `\b`. If it isn't, I do. Seem to be getting the results I wanted. Thanks.

dosboy 2010-07-13 22:24:47

ansaurus

tags:

views:

answers:

Regular Expression Word Boundary and Special Characters

related questions