$re = '/^FLST,\d+,\d+,(\d),.*?$\n((^FITEM,\d+,\d+\s*$\n)+).*?(^[^\n]*?,P51X.*?$\n)/ms';
$str = '!*
CMDELE,_Y
CMDELE,_Y1
CMDELE,_Y2
!*
FLST,2,1,5,ORDE,1
FITEM,2,33
!*
/GO
DA,P51X,ALL,
aplot
/UI,MESH,OFF
/inquire,aeChWmsy,psearch
/inquire,cGe7Wl8b,p
keyopt,etype_,1,1
*SET,areas_,0
FLST,5,2,5,ORDE,2
FITEM,5,14
FITEM,5,18
ASEL,S, , ,P51X
asum
*get,x_,area,0,cent,x
*get,y_
';
preg_match_all($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