replace tag by TAG with preg

<?php
$file=file_get_contents('yandex.html');
if($file)
{
    $new_file = preg_replace_callback('<[0-9a-z]>',function ($matches) { strtoupper($matches[0]);},$file);
    file_put_contents('yandex.html',$new_file);
};
echo($file);