<?php
 
error_reporting(-1);
mb_internal_encoding('utf-8');
 
$text = "привет.есть 2 функции,preg_split и explode ,не понимаю,в чем между ними разница.";
// Для тестов
// $text = 'roses are red,and violets are blue.whatever you do i'll keep it for you.';
// $text = 'привет.есть 2 функции,preg_split и explode ,не понимаю,в чем между ними разница.';
 
$regexp = '/[.!?]/u';
 
$sentence = preg_split($regexp, $text, -1, PREG_SPLIT_NO_EMPTY);
 
foreach ($sentence as $value){
	$value = trim($value);
	$value = mb_strtoupper(mb_substr($value, 0, 1)). mb_substr($value, -mb_strlen($value) + 1);
	$uppertext = $uppertext. $value. ". ";
};
 
$regexpArray = [
	'/[ ]+([.,:;!?])/u' => '$1',
	'/([.,:;!?])([а-яёa-z])/u' => '$1 $2'
	];
 
foreach($regexpArray as $regKey => $regValue){
	$uppertext = preg_replace($regKey, $regValue, $uppertext);
};
 
echo $uppertext;

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