$re = '/\/[A-Z]?[a-z]{1,3}[0-9]?\.exe$/m';
$str = 'hxxp://mnmassagetherapy[.]com/wp-content/uploads/2016/04/lib.exe
hxxp://seed-bc[.]com/juop4/plwr/mklo/rbn/jan2.exe
hxxp://15.204.49[.]148/files/Had.exe
hxxp://hugo.topteamlife[.]com/order/tuc5.exe';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php