shift is indeed modifying the array, but keep in mind this is the @_ array, not a globally used one. It does make a difference if you later in your subroutine would use @_, but that doesn't happen that often.

List assignment and shifting off from @_ are two very commonly used techniques to put the subroutine arguments into variables. And since @_ is not used further in the subroutine, the fact that @_ is or isn't modified is irrelevant.

Abigail