Hi,
something like

unless (-e $file) {
        open(FH,">", "$file") or die $!;
}
[download]

is almost always wrong as it's open to race conditions.

See Perl Training Australia File test operators, the garden path of race conditions and PerlMonks Avoiding race condition with sysopen for more details.

So you're better off avoiding file tests:

use Fcntl;
# Open $file for writing unless it already exists
sysopen(FH, $file, O_WRONLY|O_EXCL|O_CREAT) or die $!;
[download]

HTH,
Thomas