"$_ is string\n" if (~$_ & $_) ne '0';


##</code><code>##

my $string = "0";
my $num    = 0;

# then we:

print "string: $string is a string.\n" if ((~$string & $string) ne '0');

print "num: $num is a string.\n" if ((~$num & $num) ne '0');