$re = '/(?<= |^)(-\S+)(?= |$)/m';
$str = '-Xaa=2000 -tbb:simple -Xcc-dds -g -c -DC_hh -Xii-ff-file -Xmm-nn -Xkk -o output/gg.o -ee1481 -Xll=0x1000 -I. -I./ss/tt/uu -I./ss/tt/ww /ff/gg/vv.c -I./EIS_CFG/gentool/make -I./testenv';
preg_match_all($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