Using word boundary in regexp

Question

I'm trying to match a certain phrase using regexp, with words boundaries, but it's not working as expected. What am I doing wrong?

if (preg_match("~\b(and you[?])\b~", " and you? ")) { echo "success"; }

Does not echo "success".

However with the word boundary excluded:

if (preg_match("~(and you[?])~", " and you? ")) { echo "success"; }

It echos "success" for some reason.

You used `\b` after `[?]`, which means after `?` there must be a word char. Maybe you need `"~\b(and you[?])~"` or `"~\b(and you[?])(?!\w)~"`? — Wiktor Stribiżew, Jan 11 '17 at 13:01
It doesn't match because the word boundary after `you` is before `?` and there's no word (and therefore no word boundary) after that. — apokryfos, Jan 11 '17 at 13:07
@frosty, please check the answers and my comment. It is not really clear what kind of a word boundary you are looking for. — Wiktor Stribiżew, Jan 12 '17 at 07:27

Leon · Answer 1 · 2017-01-11T13:17:44.407

0

A word boundry does not match a question mark. So if you move the word boundry before the question mark, it will echo "success"

if (preg_match("~(\band you\b[?])~", " and you? ")) { echo "success"; }

edited Jan 11 '17 at 13:17

answered Jan 11 '17 at 13:08

Leon

The word boundary is superfluous between `you` and `?`. – Toto Jan 11 '17 at 13:10
not working, yours will match "and you?random_text" – Victor Radu Jan 11 '17 at 13:11

score 0 · Answer 2 · answered Jan 11 '17 at 13:10

in your case it will not match as the "?" is not part of a word, therefore the last \b will not match, you can try:

if (preg_match("~(\band you[?])(?=\s|$)~", " and you? ")) { echo "success"; }

which is all instances of "and you?" followed by a space type character or end of string.

2 Answers2