$re = '/build\.\d+(?![\s\S]*\bbuild\.\d+)/m';
$str = 'ICSExternalGateway-04_MJR-ICSExternalGateway-build.0 Marchen, Keith 2/25/2015 ICSExternalGateway-04_MJR-ICSExternalGateway-build.1 Marchen, Keith 2/25/2015 ICSExternalGateway-04_MJR-ICSExternalGateway-build.2 Marchen, Keith 2/25/2015 ';
preg_match_all($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