Question

I have this regex:

(?:\S)\++(?:\S)

Which is supposed to catch all the pluses in a query string like this:

?busca=tenis+nike+categoria:"Tenis+e+Squash"&pagina=4&operador=or

It should have been 4 matches, but there are only 3:
s+n
e+c
s+e

It is missing the last one:
e+S

And it seems to happen because the “e” character has participated in a previous match (s+e), because the “e” character is right in the middle of two pluses (Teni s+e+S quash).

If you test the regex with the following input, it matches the last “+”:

?busca=tenis+nike+categoria:"Tenis_e+Squash"&pagina=4&operador=or

(changed “s+e” for “s_e” in order not to cause the “e” character to participate in the match).

Would someone please shed a light on that?

Thanks in advance!

Answer 1

You are correct: The fourth match doesn’t happen because the surrounding character has already participated in the previous match. The solution is to use lookaround (if your regex implementation supports it – JavaScript doesn’t support lookbehind, for example).

Try

(?<!\s)\++(?!\s)

This matches one or more + unless they are surrounded by whitespace. This also works if the plus is at the start or the end of the string.

Explanation:

(?<!\s)  # assert that there is no space before the current position
         # (but don't make that character a part of the match itself)
\++      # match one or more pluses
(?!\s)   # assert that there is no space after the current position

If your regex implementation doesn’t support lookbehind, you could also use

\S\++(?!\s)

That way, your match would contain the character before the plus, but not after it, and therefore there will be no overlapping matches (Thanks Gumbo!). This will fail to match a plus at the start of the string, though (because the \S does need to match a character). But this is probably not a problem.