#Foo.pm
use strict;
use warnings;
package Foo;
use Foo_1.pm;
use Foo_2.pm;

# Foo_1.pm
use strict;
use warnings;
package Foo;

my $HELLO;
our $GOODBYE;
sub hello { return "Hi!"; }

# Foo_2.pm
use strict;
use warnings;
package Foo;          #note: also package Foo

#$HELLO='Bonjour'           #compiler complains - see below for why
$Foo::HELLO='Bonjour';       #this is OK - see below for why

#$GOODBYE='Au revoir'        #compiler complains - see below for why
$Foo::GOODBYE='Au revoir';   #this is OK - see below for why

# calling hello() without qualification is OK, so long
# as the package is Foo (which it is)

print hello() . ": Hello=$Foo::HELLO, Goodbye=$Foo::GOODBYE\n";