# foo.pm
package foo;
use bar;
sub import { printf("%s loaded foo\n", scalar caller) }
1;

##</code><code>##

# bar.pm
package bar;
use foo;
sub import { printf("%s loaded bar\n", scalar caller) }
1;

##</code><code>##

# script.pl
use foo;

##</code><code>##

foo loaded bar
main loaded foo