$re = '/(?<=[ \t])((?:\d{5}(?=[^\d-]|$))|(?:\d{5}-\d{4}(?=[^\d-]|$)))/m';
$str = 'Should match:
92120
11345-1234
Should not match:
92120
1234567
11345-1234567
';
preg_match_all($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