sub main {
  print "Hello, world!\n";
}

unless (caller) {
  main;
}

##</code><code>##

#!/usr/bin/perl
# File: demo.pl

use strict;
use warnings;
$|=1; # turn off buffering

use Demo qw(example);

# test() is not exported by Demo.pl
# this the error produced...
# Undefined subroutine &main::test called at C:\Projects_Perl\testing\demo.pl line 7.
# my $x = test();


my $y = Demo::test();  #this is ok , Fully qualified name
print "test() returned $y\n";

__END__
Prints:
top level in Demo.pm
this is the test subroutine!
test() returned 1

##</code><code>##

#!/usr/bin/perl
# File: Demo.pm

use strict;
use warnings;
package Demo;
use vars qw(@ISA @EXPORT @EXPORT_OK %EXPORT_TAGS $VERSION);
use Exporter;
our $VERSION=1.01;
our @ISA = qw(Exporter);
our @EXPORT    = qw();
our @EXPORT_OK = qw(example);
     
our $DEBUG =0;
test() if !caller; # runs test() if run as a "main program"

sub test { print "this is the test subroutine!\n"; return 1;}

sub example {return "this is an example"};

print "top level in Demo.pm\n";


1;