$re = '/\\\\(?<=(0_ASW|10_BSW)\\\\)([A-Za-z0-9]+)/m';
$str = 'C:\\MyPath\\0_ASW\\Mod2000
C:\\MyPath\\0_ASW\\Mod2005\\SubDir
C:\\MyPath\\10_BSW\\ModA\\SubDir
C:\\MyPath\\10_BSW\\ModB
C:\\MyPath\\10_BSW\\ModC\\
';
preg_match_all($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