How can str_replace only last?

Question

PHP

Like str_replace only the last . on _home

$string = 'thumbs/2015/03/220px-Harvard_Wreath_Logo_1.svg-pvWrLY0xXuP1RbkQ8fJkHgbHFqKnmciQ.png'

should be

thumbs/2015/03/220px-Harvard_Wreath_Logo_1.svg-pvWrLY0xXuP1RbkQ8fJkHgbHFqKnmciQ_home.png

Answer 1

possible extensions are known in advance?
(\.)(png|jpg|итд)$

Answer 2

$string = 'thumbs/2015/03/220px-Harvard_Wreath_Logo_1.svg-pvWrLY0xXuP1RbkQ8fJkHgbHFqKnmciQ.png';
$string = preg_replace('/(\.[^\.]+$)/', '_home$1', $string);
echo $string;