$re = '/\/?({[a-zA-Z_0-9]*})\/?/';
$str = '# Valid
/test3/{id}/{test}/{id}
# Valid
/admin/{slug}
# Not Valid
/test3{id}{test}
# Not Valid
/test/{id}/yyy/{dd}/dwdw/{wd}{d}
# Valid
/user/post/{id}
# Valid
/{tt}/{t}
# Valid
/test/{id}/yyy/{dd}////dwdw/{wd}/{d}
';
preg_match_all($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