Question

I’m trying to formulate a regular expression that will allow me to find a string within a piece of text, if the string exists on its own i.e. not within another word (but surrounded by special characters is ok).

/\bword\b/i

The above regex works fine, and finds “word” in the text. The problem comes when the word I want to find is something like “c++”. In this case it matches on any occurrence of the “c” character on it’s own. I’ve tried escaping the “+” characters but it doesn’t make any difference. I’m assuming because “+” is a non-word character, I’m possibly going down the wrong route and using word boundaries is not what I should be doing.

So I guess the question is, how can I use a regular expression to find a string in a piece of text, on it’s own, and regardless of whether the string is alphanumeric or contains special characters. So in the following piece of text it should match on the 3 occurences of “c++”:

c++
(c++)
perl/c++/assembly

But it should not match on the following:

maniac++
c++abc

This is intended so that my script can tell if a specific skill exists within a user’s CV/resume. I’m using this with PHP’s preg_match_all() function.

I’ve done a lot of searching but can’t come up with a solution, hopefully someone with good regex knowledge can help.

Answer 1

Try this:

/(?<!\w)(c\+\+)(?!\w)/

The (?<!\w) is a negative lookbehind clause, meaning that a word character should not immediately precede your pattern. The (?!\w) part is negative lookahead, meaning that a word character should not immediately follow.

Hope this helps!