$re = '`TRN\*[^~\\\\]+`m';
$str = 'ENTRY DESCR:HCCLAIMPMTSEC:CCD TRACE#:04858562 TRN*1*6523251452*5865418282584~
ENTRY DESCR:HCCLAIMPMTSEC:CCD TRACE#:04526412 TRN*1*5685952452*158615*6526352 26\\ TRN: 563569856';
preg_match_all($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