$re = '/^(\d{4}|\d{2})\/(0?[1-9]|1[0-2])\/(0?[1-9]|[12]\d|3[01]), ([AP])M([1-9]|1[0-2]):([0-5]\d) - (.*?): (\D*(?:\d(?!(?:\d{3}|\d)\/(?:0?[1-9]|1[0-2])\/(0?[1-9]|[12]\d|3[01]))\D*)*)(?=\n|$)/m';
$str = '2012/12/1, AM12:21 - user1: entry1_wasehhjdsaj
2012/12/2, AM9:42 - user2: entry2_bahbahbah_dsdeead
2012/12/2, AM9:44 - user3: entry3_Line1_ContdWithFollowingLine_bahbah
entry3_Line2_ContdWithABoveLine_bahbahbah_erererw
entry3_Line3_ContdWithABoveLine_bahbahbah_dsff
2012/12/4, AM11:48 - user7: entry4_bahbahbah_fggf';
preg_match_all($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