How much percent the string match the regex - php

Question

Basically, I just wondering if exists a function like this:
$string = 'helloWorld';
// 1 uppercase, 1 lower case, 1 number and at least 8 of length
$regex = '/^\S*(?=\S{8,})(?=\S*[a-z])(?=\S*[A-Z])(?=\S*[\d])\S*$/'
$percent = matchPercent($string, $regex);
echo "the string match {$percent}% of the given regex";
Then, the result could be something like this:
the string match 75% of the given regex
Seeing another post and question, I can do somehitng like this:
$uppercase = preg_match('#[A-Z]#', $password);
$lowercase = preg_match('#[a-z]#', $password);
$number = preg_match('#[0-9]#', $password);
But, the goal is to work with any regex pattern at the function

Answer 1

If you want to do it the regex way and based on the use-case you've provided, we need to make the whole regex optional. Also we'll be using capturing groups in our lookaheads.
But first things first, let's improve your regex:
[\d] is redundant, just use \d.
\S*(?=\S{8,}) remove \S* part, we already have it at the end.
Our regex will look like ^(?=\S{8,})(?=\S*[a-z])(?=\S*[A-Z])(?=\S*\d)\S*$
Now is the tricky part, we will add groups in our lookaheads and make them optional:
^(?=(\S{8,})?)(?=(\S*[a-z])?)(?=(\S*[A-Z])?)(?=(\S*\d)?)\S*$
You might ask why? The groups are made so that we can track them later on. We make them optional so that our regex will always match. That way, we can do some math!
$regex = '~^(?=(\S{8,})?)(?=(\S*[a-z])?)(?=(\S*[A-Z])?)(?=(\S*\d)?)\S*$~';
$input = 'helloWorld';
preg_match_all($regex, $input, $m);
array_shift($m); // Get rid of group 0
for($i = 0, $j = $k = count($m); $i < $j; $i++){ // Looping
if(empty($m[$i][0])){ // If there was no match for that particular group
$k--;
}
}
$percentage = round(($k / $j) * 100);
echo $percentage;
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Answer 2

EDIT: I see that Hamza had pretty much the same idea.
Sure! That's a really fun question.
Here is a solution for a simplified validation regex.
$str = 'helloword';
$regex = '~^(?=(\S{8,}))?(?=(\S*[a-z]))?(?=(\S*[A-Z]))?(?=(\S*[\d]))?.*$~';
if(preg_match($regex,$str,$m)) {
$totaltests = 4;
$passedtests = count(array_filter($m)) -1 ;
echo $passedtests / $totaltests;
}
Output: 0.5
How does it work?
For each condition (expressed by a lookahead), we capture the text that can be matched.
We define $totaltests as the total number of tests
We count the number of tests passed with count(array_filter($m)) -1 which removes the empty groups and Group 0, i.e. the overall match.
We divide.