PerlOnTheWay has asked for the wisdom of the Perl Monks concerning the following question: 

package A;
package B;
our $d = 1;
package C;
package D;
print $d;

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the above prints 1,but how does it work actually?

$d is not defined in package D, how can it be printed directly?

Replies are listed 'Best First'.
Re: Perl syntax
by stevieb (Canon) on Mar 27, 2012 at 01:58 UTC

    From 'perldoc -f our'

    An "our" declaration declares a global variable that will be visible a
+cross its entire lexical scope, even across package
boundaries.

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    So any variable initialized with my or our is in this case within file scope. Wrap the instantiation of $d within a block to make the scope smaller:

    package A;
package B;
{ our $d = 1; }
package C;
package D;
# now you have to use the package name to access the var
print $B::d;

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Re: Perl syntax
by chromatic (Archbishop) on Mar 27, 2012 at 01:46 UTC
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Re: Perl syntax
by kcott (Archbishop) on Mar 27, 2012 at 02:00 UTC

    See our for more details; including an example similar to yours. (Note: that's a different our link to what chromatic provides above.)

    -- Ken

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Re: Perl syntax
by JavaFan (Canon) on Mar 27, 2012 at 09:19 UTC
    our makes a lexically scoped alias to a package variable. So, 
    package B;
our $d = 1;

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    means that for the rest of the lexical scope (in your case, the current file (and of course not if it's hidden by a definition in an inner scope)), $d is an alias to $B::d. So, your code is equivalent to: 
    package A;
package B;
$B::d = 1;
package C;
package D;
print $B::d;

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    Don't worry if you find it confusing; many people do. Luckely, you don't have to use it. I find myself using it only for variables like @ISA and @EXPORT.
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