$re = '/(\d*)(.+?)(,)()/m';
$str = '1MASS,2BLOCKCOUNT,3SECTOR,4SYSTEM,
FIRST DISPLAY BLOCK REGEX COMMAND
[REPLACEALL](\\d*)(.*?)(,)()[WITH] $1 $2
$4';
$subst = " $1 $2\n$4";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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