#!/usr/bin/perl 
use lib ".";
use A;
use B; 
def();
######################################## 
A.pm 
package A;
require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(abc); 
use C;
######################################## 
B.pm 
package B;
require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(def);
use C; 

sub def{
    print "Inside sub def of package B -> calling sub abc from package C\n";
    abc();
}
######################################## 
C.pm 
package C;
require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(abc); 

sub abc{
    print "Inside sub abc of package A\n";
}