$re = '/\b([1-9][0-9]{5})\b/m';
$str = '1 :- ho no 55 A Akbarpur Behrampur vijay nagar 7827183008 Ghaziabad UP 201009
2 :- 47- A 57798/4343 ward no 7 ghaziabad 201009 UP
3 :- 45456/343 ward 76587 Lucknow 110087
4 :- ho no 55 a behrampur ghaziabad 210 501';
preg_match_all($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