$re = '/(?<=\"fileAssetId\":\")[a-fA-F0-9-]+?(?=\")|(?<=\"filename\":\").+?(?=\")/';
$str = '\'{"d":{"__type":"WikiFileNodeContent:http:\\/\\/samplesite.com.u\\/ns\\/business\\/wiki","author":null,"description":null,"fileAssetId":"034b9317-60d9-45c2-b6d6-0f24b59e1991","filename":"Reports.pdf"},"createdBy":1531,"createdByUsername":"John Cash","icon":"\\/Assets10.37.5.0\\/pix\\/16x16\\/page_white_acrobat.png","id":3041, "filename":"test", "inheritedPermissions":false,"name":"map","permissions":[23,87,35,49,65],"type":3,"viewLevel":2},{"__type":"WikiNode:http:\\/\\/samplesite.com.au\\/ns\\/business\\/wiki","children":[],"content"\'';
preg_match_all($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