Question

I’m using PHP’s preg_replace, and trying to transform the string

abcd

into

(a(b(c(d))))

This is the best I’ve got:

preg_replace('/.(?=(.*$))/', '$0($1)', 'abcd');
// a(bcd)b(cd)c(d)d()

Is it even possible with regex?

Edit I’ve just discovered this in the PCRE spec: Replacements are not subject to re-matching, so my original approach isn’t going to work. I wanted to keep it all regex because there’s some more complicated matching logic in my actual use case.

Answer 1

I went with something along the lines of a combination of the above answers:

preg_match_all('/./ui', 'abcd', $matches);
$matches = $matches[0];
$string = '('.implode('(', $matches).str_repeat(')', count($matches));