What are all the false values in Perl ((conditional, boolean, whitespace, unprintable characters)

princepawn has asked for the wisdom of the Perl Monks concerning the following question:

The following simple subroutine:

sub log_msg {
  my $log_msg = shift;
  print "value $script::debug";
  if ($script::debug) {
      print sprintf "(%s) $log_msg \n", shell_date;
  }
}
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still prints log messages when the printed value of $script::debug is 0.

So this yields two questions, and I would like an answer to both:

What are all the false values in Perl? I know of the following:

How do one brute-force print every character in a string even if it is typically unprintable? That is, my guess is that things are being printed even when $script::debug appears to be zero when in fact there may be some hidden control char or something in the string.

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