Perl String - Substitute Characters without forming a new variable

Is it possible to replace parts of a string without having to create a whole new variable?

Right now I do it like this:

$someString = "how do you do this";
$someString = s/how do/this is how/;

What I am trying to do is keep the original string ($someString) and be able to substitute a few characters without modifying the original string. Im more familiar with Javascript and I can do it like this in your code without having to create/modify a variable.

someString.replace(/how do/, "this is how")

Any help is appreciated, thanks alot