[Regular expression] how can I match "match with a string end or end" such as mv&id=17328895840&scm=102 and mv&id=17328895840?

[Regular expression] ask how to "match the end or end of a string." For example, mv&id=17328895840&scm=102 and mv&id=17328895840 can all match
Example:

str = mv&id=17328895840&scm=102

Reg = "/&id= (./) &/u";

This should be able to fetch 17328895840.

But mv&id=17328895840, this is not going to match.

I tried the next reg = "/&id= (./) [&|$]/u";

Ask how to write a regular to match both of these situations

Thank you

------Solution--------------------
$reg = = "/&id= (. +) (?:&
------Solution--------------------
$)/U ";
------Solution--------------------
$reg = "/&id= (. +?) (&
------Solution--------------------
$)/";

