<?php
$re = '~^\h*F\d{6}.*?\R{2}\K~ms';
$str = "A N K U N F T 11.08.15\n*** NEUBUCHUNG ***\n 11.08.15 xxx xxx X3 2830 14:25 17:50\n 18.08.15 xxx xxx X3 2831 18:40\n F882129 dsdsaidsaia\n F882129 xxxyxyagydaysd\nsadsdsdsdsadsadadssda\nsadsdsdsdsadsadadssda\n\nA N K U N F T 18.08.15\n*** NEUBUCHUNG ***\n 11.08.15 xxx xxx X3 2830 14:25 17:50\n 18.08.15 xxx xxx X3 2831 18:40\n F881554 ZXCXZCXCXZCCXZ\n F881554 xcvcxvcxvcvxc\n F881554 xvcxvcxcvxxvccvxxcv\n\n\n11.08.15 xxx xxx X3 2830 14:25 17:50\n 18.08.15 xxx xxx X3 2831 18:40\n F881605 xczxcdfsfdsdfs\n F881605 zxccxzxzdffdsfds\n\n";
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