PHP Regex for nested patterns

Question

I have the following PHP string:

$str = "a b [[c], [d] then [e]] followed by [f] then [g]";

I'm trying to write 2 expressions in PHP; one to extract the [c], [d], [e] (including the square brackets) and a second regex to extract the [f] and [g] (including brackets).

Bonus points for anyone who can do it with whitespace added before or after a square bracket.

Does anyone have any ideas?

Thanks :)

http://stackoverflow.com/questions/133601/can-regular-expressions-be-used-to-match-nested-patterns — tiguchi, Sep 13 '15 at 16:50
What's your expected output if the input is `[fs[sc][sc[gf]]]` ? — Avinash Raj, Sep 13 '15 at 16:54
Any attempts so far? If it's always just two levels of brackets then it doesn't even require a nested pattern. — mario, Sep 13 '15 at 16:59

score 0 · Answer 1 · answered Sep 13 '15 at 20:15

You can try with this simple and readable regex (for two levels only and balanced brackets):

(?|(?<=\[)[^\[\]]*(?<nested>\[[^\[\]]+\])[^\[\]]*|(?<=(?!\A)\G)(\[[^\[\]]*\])[^\[\]]*(?=(?:[^\[\]]*\[[^\[\]]+\])*\])|(?<=(?!\A)\G)[^\[\]]*(\[[^\[\]+]\])[^\[\]]*(?=\]))|(?<simple>\[[^\[\]]+\])

DEMO

I'm pretty sure, that there is (probably better) way to do that without regex, but this is how I would do that with regex. Probably there is also better way to do that with regex :D

About whitspaces before and after brackets, I don't know what you mean: inside or outside brackets? add whitspaces, or match whitspaces if its occour before or after bracket?

PHP Regex for nested patterns

1 Answers1