RegExp match group not preceded by alphanumeric (\w) ignoring spaces - php

Question

I'm trying to match a group that only matches when the first non-spacing character preceding the match is NOT an alphanumeric character.
RegExp i've tried, consuming the spaces first with \s* then looking behind to check for \w:
(?<!\w)\s*\({\w+}\)
Success
Input: this will = ({match})
Expected: ({match})
Actual: ({match})
Failure, still matches while preceded by alphanumeric (ignoring spaces)
Input: this should = not ({match})
Expected: -
Actual: ({match})
Using \s+ instead of \s* solved it partially but now it requires at least one space which is not desired!
(?<!\w)\s+\({\w+}\)
I've been looking around the internet but cannot solve the problem. Anyone?

Answer 1

Use this solution (a mix of #horcrux and #Wiktor Stribizew suggestions):
<?php
$regex = '/(?<![\w\s])\s*(\({\w+}\))/';
$string = 'this will = ({match})
this should = not ({match})';
preg_match_all($regex, $string, $matches);
var_dump($matches[1]);
?>
See regex proof.
Results:
array(1) {
[0]=>
string(9) "({match})"
}
See PHP proof.
EXPLANATION
--------------------------------------------------------------------------------
(?<! look behind to see if there is not:
--------------------------------------------------------------------------------
[\w\s] any character of: word characters (a-z,
A-Z, 0-9, _), whitespace (\n, \r, \t,
\f, and " ")
--------------------------------------------------------------------------------
) end of look-behind
--------------------------------------------------------------------------------
\s* whitespace (\n, \r, \t, \f, and " ") (0 or
more times (matching the most amount
possible))
--------------------------------------------------------------------------------
( group and capture to \1:
--------------------------------------------------------------------------------
\( '('
--------------------------------------------------------------------------------
{ '{'
--------------------------------------------------------------------------------
\w+ word characters (a-z, A-Z, 0-9, _) (1 or
more times (matching the most amount
possible))
--------------------------------------------------------------------------------
} '}'
--------------------------------------------------------------------------------
\) ')'
--------------------------------------------------------------------------------
) end of \1

Answer 2

If there has to be a first non-spacing character present, you could match it and use \K to clear the match buffer.
[^\w\s]\h*\K\({\w+}\)
The pattern matches
[^\w\s] Match a single char other than a word char or whitespace char
\h*\K Match 0+ horizontal whitespace chars and forget what is matched so far
\({\w+}\) Match 1+ word chars between ({ and })
Regex demo | Php demo