<?php

$string = "test is the {COMMAND line -STRET (interface 5more 9words #here";
$strlowercase = strtolower($string);

$result = preg_replace_callback('~(^|[^a-zA-Z])([a-z])~', function($matches)
{
    return $matches[1] . ucfirst($matches[2]);
}, $strlowercase);

var_dump($result);