regex to remove all whitespaces except between brackets

Question

I\'ve been wrestling with an issue I was hoping to solve with regex.

Let\'s say I have a string that can contain any alphanumeric with the possibility of a substrin

Answer 1

Resurrecting this question because it had a simple solution that wasn't mentioned.

\[[^]]*\](*SKIP)(*F)|\s+

The left side of the alternation matches complete sets of brackets then deliberately fails. The right side matches and captures spaces to Group 1, and we know they are the right spaces because if they were within brackets they would have been failed by the expression on the left.

See the matches in this demo

This means you can just do

$replace = preg_replace("~\[[^]]*\](*SKIP)(*F)|\s+~","",$string);

Reference

1. How to match pattern except in situations s1, s2, s3
2. How to match a pattern unless...