use strict;
use Filesys::Df;

my $fobj = df("/");
print commify($fobj->{bavail} * 1024) . " bytes of "
        . commify($fobj->{blocks} * 1024) . " bytes free\n";

sub commify {
        my $text = reverse $_[0];
        $text =~ s/(\d{3})(?=\d)(?!\d*\.)/$1,/g;
        return scalar reverse $text;
}