sub sys_true_rand {
   my ($num_char) = @_; # Число символов в качестве параметра.                       
   my $dev_line;
   my $rand_line = "";
   open(UR,"</dev/urandom") || die "Cam't open /dev/urandom"";
   do {
        read (UR, $dev_line, 4096);
        $dev_line =~ s/[^\w\d]//g;
        $rand_line .= $dev_line;
   } until (length($rand_line) >= $num_char);
   close(UR);
   return substr($rand_line,0, $num_char);
}