use constant 
    {
        MY_CONSTANT1 => 1,
        MY_CONSTANT2 => 2,
        MY_CONSTANT3 => 3,
        MY_CONSTANT4 => 4
    };

sub useConstants
{
   #able to use constants fine in here...
   my $var = MY_CONSTANT4;
   print "$var\n"; #outputs '4'
}

1;

##</code><code>##

#!/usr/bin/perl

#use strict;  # If I uncomment this line it won't compile because it claims MY_CONSTANT3 is a bareword and not a constant.

require "constants.pl";

#if I call useConstants this sub can use them just fine.
useConstants();

#However if I try to use a constant that should've been defined in constants.pl here it won't work!
my $var = MY_CONSTANT3;
print "$var\n"; #outputs 'MY_CONSTANT3'  !!  Why won't it output '3'?

exit 1;

##</code><code>##

me@mybox:/test
>perl main.pl
4
MY_CONSTANT3
me@mybox:/test
>