use strict;
use vars qw($foo);
# ... code that uses $foo ...
1;

##</code><code>##

use strict;
use Library;
# You can now use $foo freely.

##</code><code>##

use vars qw($foo);
# Some code here.

package Bar;
# Now you can't use $foo, and won't accidentally access $main::foo.

##</code><code>##

package Foo;
use strict;
use Exporter qw(import);
our @EXPORT_OK = qw(foo);
# etc
1;

##</code><code>##

package Foo;
use strict;
use Exporter qw(import);
use vars qw(@EXPORT_OK);
@EXPORT_OK = qw(foo);
# etc
1;

##</code><code>##

package Foo;
use Exporter qw(import);
@EXPORT_OK = qw(foo);
use strict;
# etc
1;