$re = '/(\([^()]*\)[[:blank:]][[:blank:]]*)[^()]*\([^()]*\.([^()]*)\)/m';
$str = 'TREE(abc/x73/APPLE) DEST(MYFILE.FILE1A)
TREE(abc/x74/APPLE) DEST(MYFILE88.FILE1A)
TREE(abc/x100/APPLE) DEST(MYFILE100.FILE1B)
TREE(abc/x61/APPLE) DEST(MYFILE1000.FILE1A)';
$subst = "$1$2";
$result = preg_replace($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