$re = '/(?<timestamp>.{15}) (?<host>[^ ]*) (?<seqno>[^ ]*) (?<ignore>[^%]*) (?<log_type>[^:]*): (?<message>.*)/';
$str = 'Jan 31 23:59:58 192.168.3.121 1246088: Jan 31 23:59:57: %SEC-6-IPACCESSLOGP: list VTYACCESS denied tcp 59.1.188.127(2159) -> 0.0.0.0(23), 1 packet';
preg_match_all($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