PHP regular expression to replace nested () with []

Question

I am trying to match a string, see example, such that a nested parantheses () is replaced by [] so to not break a parser somewhere else. In this case, I would like to replace t

Answer 1

You can't do this reliably with regular expressions. If you choose to go with this method anyway, the answer depends on what assumptions you're willing to make about the input. If, for example, you're willing to assume the innermost parentheses can be replaced, the answer is easy:

preg_replace('!\(([^()]*)\)!', '{$1}', $input);

If you're specifically looking for nested parentheses, try:

preg_replace('!\(([^()]*)\(([^()]*)\)([^()]*)\)!', '($1{$2}$3)', $input);