- preg_replace: documentation ( source)
<?php
$re = "/^((?:\d{2}\.?){3}).*?(\w{2}\s\d{4}).*?(\d{2}:\d{2})(?:.*?(\b[a-z]+\b).*?(\b[a-z]+\b))?$/m";
$str = "A N K U N F T 11.08.15
*** NEUBUCHUNG ***
11.08.15 xxx xxx X3 2830 14:25 17:50
18.08.15 xxx xxx X3 2831 18:40
F882129 dsdsaidsaia
F882129 xxxyxyagydaysd
A N K U N F T 18.08.15
*** NEUBUCHUNG ***
11.08.15 xxx xxx X3 2830 14:25 17:50
18.08.15 xxx xxx X3 2831 18:40
F881554 ZXCXZCXCXZCCXZ
F881554 xcvcxvcxvcvxc
F881554 xvcxvcxcvxxvccvxxcv
11.08.15 xxx xxx X3 2830 14:25 17:50
18.08.15 xxx xxx X3 2831 18:40
F881605 xczxcdfsfdsdfs
F881605 zxccxzxzdffdsfds ";
$re = "/(?:\sF\d+.*?\n\n)(\n)/";
$subst = ">>CUT HERE>>";
$result = preg_replace($re, $subst, $str);
echo $result;
?>