$re = '/(?:^|\D)[56]\d{5,6}(?!\d)/m';
$str = '5494398 70008 \'order # 5494398 Product#: 70008
5001447452 \' should be ignored
6415366 OSW SHIP 70052 \'order # 6415366 Product#: 70052
6567598y7058 Nov 20 \'order # 6567598 Product#: 7058
OSW SHIP 70054 RH STRONGBACKS \'order # N/A Product#: 70054
OSW HS 70052 70053 \'order # N/A Product#: 70008
6511534 04450 \'order # 6511534 Product#:either 04450 or 0445 (this is only case)
6511538 0046 \'order # 6511538 Product#: 0046
0046 6387125 \'order # 6387125 Product#: 0046
OSW 70032 \'order # N/A Product#: 70032
OSW HEX Blots 046 047 048 049 \'order # N/A Product#: 064 & 047 & 048 & 049 (4 matches)';
preg_match_all($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