<?php

$input = "Bet you want a BMW.";
echo preg_replace(
    "/([a-z]*)/Xe", "strtoupper('\\1')", $input);

echo preg_replace(
    '|^(.*)$|ei',
    '"\1"',
    'get_input');

$html = preg_replace('(<h([1-6])>(.*?)</h\1>)sex','"<h$1>" . strtoupper("$2") . "</h$1>"', $html);

$a = preg_replace(
    '#<h([1-6])>(.*?)</h\1>#e',
    '"<h$1>" . strtoupper("$2") . "</h$1>"',
    $html
);

$string = 'April 15, 2003';
$replacement = '${1}1,$3';
$b = preg_replace('/(\w+) (\d+), (\d+)/i', $replacement, $string);