Programming Perl, 4th Edition

Lexically Scoped Global Declarations: our

In the old days before use strict, Perl programs would simply access global variables directly. A better way to access globals nowadays is by the our declaration. This declaration is lexically scoped in that it applies only through the end of the current scope. However, unlike the lexically scoped my or the dynamically scoped local, our does not isolate anything to the current lexical or dynamic scope. Instead, it provides “permission” in the current lexical scope to access a variable of the declared name in the current package. Since it declares a lexical name, it hides any previous lexicals of the same name. In this respect, our variables act just like my variables.

If you place an our declaration outside any brace-delimited block, it lasts through the end of the current compilation unit. Often, though, people put it just inside the top of a subroutine definition to indicate that they’re accessing a global variable:

sub check_warehouse {
    our @Current_Inventory;
    my  $widget;
    foreach $widget (@Current_Inventory) {
        say "I have a $widget in stock today.";
    }
}

Since global variables are longer in life and broader in visibility than private variables, we like to use longer and flashier names for them than for temporary variables. This practice alone, if studiously followed, can do nearly as much as use strict can toward discouraging the overuse of global variables, especially in the less prestidigitatorial typists.

Repeated our declarations do not ...