PHP: How to capitalize first letter of first word in a sentence, including a set of non-ASCII values?

Question

I found an answer here: How to capitalize first letter of first word in a sentence? however, it doesn't work when the sentence starts with characters such as " or «.

The code found in the link above is:

$output = preg_replace('/([.!?])\s*(\w)/e', "strtoupper('\\1 \\2')", ucfirst(strtolower($input)));

Here's an example of the handling I need

$input  => «the first article title» 
$output => «The first article title»

$input  => « the first article title »
$output => « The first article title »

$input  => "être"
$output => "Étre"

The idea is to ignore any non alphabetic (not in [a-z, A-Z] + french characters) and apply to the first alphabetic one and the rest will remain the same as the input.

Answer 1

Apply a limit so that only 1 character is replaced:

$output = preg_replace('/[a-z]/e', 'strtoupper("$0")', strtolower($input), 1);

Though you should be using preg_replace_callback() rather than the /e switch nowadays:

$output = preg_replace_callback(
    '/[a-z]/',
    function($matches) { return strtoupper($matches[0]); },
    strtolower($string),
    1
);

EDIT

After the scope creep of changing the question to require UTF8 handling:

$output = preg_replace_callback(
    '/\p{L}/u',
    function($matches) { return mb_strtoupper($matches[0]); },
    mb_strtolower($string),
    1
);