Using Global Variables in Perl

[gzayzay]

Hi Monks, I am a Perl rookies that seek you wisdom. I am working on a project and I need to parse around some variables to separate modules I have created. Example:

use strict;
use var qw($readMode $writeMode $appendMode);

$readMode   = '';
$writeMode  = '>';
$appendmode = '>>';

sub openFile
{
my $mode = pop(@_)
open(FILENAME, $mode, EXPR);
}

I have multiply mudules that I will like to use the various file modes that I have define in this module say called "moduleA". In moduleB that is locate in a separate file, I use the following code;

use strict;

require "moduleA.pl";
openFile("someOtherStuff", $readMode);

Whenever I run the code, I see the following error "Global symbol "$readMode" requires explicit package name at ..." Could any Monk kindly fill me with wisdom? note, I don't want to $readMode by way of a subroutine. Thanks