# file foo.pl
use strict;
our $foo; # that's $main::foo

{
    package Foo;
    our $foo = "foo"; # package variable $Foo::foo created
    print __FILE__,' ',__LINE__,' ',__PACKAGE__,":: \$foo is '$foo'\n";

    package Bar;
    print __FILE__,' ',__LINE__,' ',__PACKAGE__,":: \$foo is '$foo'\n";
}
print __FILE__,' ',__LINE__,' ',__PACKAGE__,":: \$foo is '$foo'\n";
print __FILE__,' ',__LINE__,' ',__PACKAGE__,":: \$Foo::foo is '$Foo::foo'\n";

##</code><code>##

# file bar.pl
use strict;

{
    package Bar;
    our $foo; # package variable $Bar::foo created
    print __FILE__,' ',__LINE__,' ',__PACKAGE__,":: \$foo is '$foo'\n";
} # end of scope

package Foo;
our $foo; # package variable $Foo::foo initialized in 'foo.pl'
print __FILE__,' ',__LINE__,' ',__PACKAGE__,":: \$foo is '$foo'\n";

package Bar;
print __FILE__,' ',__LINE__,' ',__PACKAGE__,":: \$foo is '$foo'\n";

##</code><code>##

#!/usr/bin/perl

use strict;
our $foo = 'bar'; # package variale main::foo
require 'foo.pl';
require 'bar.pl';

print __FILE__,' ',__LINE__,' ',__PACKAGE__,":: \$foo is '$foo'\n";

##</code><code>##

foo.pl 8 Foo:: $foo is 'foo'
foo.pl 11 Bar:: $foo is 'foo'
foo.pl 13 main:: $foo is 'bar'
foo.pl 14 main:: $Foo::foo is 'foo'
bar.pl 7 Bar:: $foo is ''
bar.pl 12 Foo:: $foo is 'foo'
bar.pl 15 Bar:: $foo is 'foo'
main.pl 8 main:: $foo is 'bar'