another thing. if you do not need STDERR you can do a dirty trick! ;)

#!/usr/bin/perl -w

use strict;
use warnings;

if ( $^O =~ /^(MS)?Win/ ) {
    eval {
        #dirty hack to avoid the warning
        close STDERR;
        require Win32::DriveInfo;


        my $TotalNumberOfFreeBytes = (Win32::DriveInfo::DriveSpace('c:
+'))[6];
        my $TotalNumberOfBytes = (Win32::DriveInfo::DriveSpace('c:'))[
+5];

        print "This is $^O \n";
        print "Total Free: $TotalNumberOfFreeBytes\tTotal size: $Total
+NumberOfBytes\n";
    };
    print $@, "\ndone!";
}
elsif ( $^O =~ /^linux/ ) {
    print "This is Linux OS!!!\n";
}
[download]

HTH