$re = '/(?:sampledata=(\S+)|(?!^)\G)[^F]*(?:F(?!FAB[0-9]_[0-9]=)[^F]*)*?(FAB[0-9]_[0-9])=([0-9]*)/';
$str = 'sampledata=X
B : xyz=1 FAB1_1=03 FAB2_1=01
A : xyz=1 FAB1_1=03 FAB2_1=01
';
preg_match_all($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