php - Making first character of all sentences upper case -

i have function suppose make first character of sentences uppercase, reason, it's not doing first character of first sentence. why happening, , how fix it?

<?php  function ucall($str) {  $str = preg_replace_callback('/([.!?])\s*(\w)/',  create_function('$matches', 'return strtoupper($matches[0]);'), $str); return $str;  } //end of function ucall($str)  $str = ucall("first.second.third"); echo $str;  ?> 

result:

first.second.third 

expected result:

first.second.third 

it not uppercase first word because regular expression requires there 1 of ., ! or ? in-front of it. first word not have 1 of characters in-front of it.

this it:

function ucall($str) {     return preg_replace_callback('/(?<=^|[\.\?!])[^\.]/', function ($match) {         return strtoupper($match[0]);     }, $str); } 

it uses positive look-behind make sure 1 of ., !, ?, or start of line, in-front of matched string.