Do it with objects.

File1.pl:

use strict;
use warnings;
use File2;

my $file2obj = File2->new();
print "var: " . $file2obj->{var} . "\n"; #should print 1
$file2obj->{var} = 10 . "\n";
print "var: " . $file2obj->{var}; #should print 10
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File2.pm:

package File2;
use strict;
use warnings;
use fields qw(var); # to keep yourself from making stupid typos, like 
+calling $file2obj->{vaar};

sub new {
  my $package = shift;
  my $self = fields::new($package);
  $self->{var}=1; # initialize var;
  return $self;
}
1;
[download]

Now for a followup... how would you do that in perl6? ;)