How to optimally find the first occurrence of a substring before any character that is not a letter?

Question

PHP

Let's say there is a string,
$str = 'Синее море'
but it can also be
$str = 'Синее. Море'
How is it best to find "Blue"? That is, find the first occurrence of a substring up to a non-letter character?

Answer 1

That is, find the first occurrence of a substring up to a non-letter character?

The problem in this formulation can be reformulated:

$str = 'Синее. Море';
if (preg_match('/^\w+/u', $str, $match)) {
    echo $match[0];
}