Regex negative lookbehind on string

Question

I cannot seem to be able to find a way to not return a match if a string exists but not immediately before another string.

I am able to not return a match if a string exists immediately before another string, with the following.

$string = 'Stackoverflow hello world foobar test php';

$regex = "~(Stackoverflow).*?(?<!(test\s))(php)~i";

if(preg_match_all($regex,$string,$match))
    print_r($match);

In this example, we want to return a match if we have the word Stackoverflow and php but only if the word test(with a space character) does not exist before the word php.

This doesn't return any result which is good.

Lets now say I want to match php but only if the word foobar doesn't exist somewhere between Stackoverflow and php, I assumed I could do the following.

$string = 'Stackoverflow hello world foobar test php';

$regex = "~(Stackoverflow).*?(?<!(foobar)).*?(php)~i";

if(preg_match_all($regex,$string,$match))
    print_r($match);

(I have changed the negative look behind string to (foobar), and added .*? after)

I would also like to say that I cannot always know what words will exist between foobar and php, sometimes there will be none, sometimes 200, but I do have some positioning information (after Stackoverflow and before php).

Answer 1

I would use a negative lookahead to ensure the string 'foobar.*php' does not exist after 'stackoverflow' And since you wanted to capture php, I'd put that into a capturing group. Something like:

Stackoverflow(?:(?!foobar.*php).)*(php)

Note that this results in checking after each character