if you want to extract all {token}s from a string:
<?php
$pattern = "/{[^}]*}/";
$subject = "{token1} foo {token2} bar";
preg_match_all($pattern, $subject, $matches);
print_r($matches);
?>
output:
Array
(
[0] => Array
(
[0] => {token1}
[1] => {token2}
)
)