Поисковый тест по началу и конец

<?php
$str = 'Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. ...';

$start = 'sadipscing';
$end = 'dolore';

$pattern = sprintf(
    '/%s(.+?)%s/ims',
    preg_quote($start, '/'), preg_quote($end, '/')
);

if (preg_match($pattern, $str, $matches)) {
    list(, $match) = $matches;
    echo $match;
}
Splendid Stoat