Regex for checking if a string has mismatched parentheses?

Question

In a PHP script, what regex should I use to check for mismatched parentheses in a string? Things that I want to allow include:

• This is (ok)
• This (is)

Answer 1

Your examples don't include any nested parentheses… if you aren't concerned with nesting, then this can be done using the following expression:

^[^()]*(?:\([^()]*\)[^()]*)*$

This will match against all the strings in your "allow" list and fail against the strings in your "prevent" list. However, it will also fail against any string with nested parentheses. e.g. "this (is (not) ok)"

As others have already pointed out, regular expressions are not the correct tool if you need to handle nesting.