Challenge 45: Cyphers and Quines
Challenge 1
The square secret code mechanism first removes any space from the original message. Then it lays down the message in a row of 8 columns. The coded message is then obtained by reading down the columns going left to right.
For example, the message is “The quick brown fox jumps over the lazy dog”.
Then the message would be laid out as below:
thequick
brownfox
jumpsove
rthelazy
dog
The code message would be as below:
tbjrd hruto eomhg qwpe unsl ifoa covz kxey
Write a script that accepts a message from command line and prints the equivalent coded message.
So, to me, much of this involves things I’ve use and I think talked about here before, like using regexes and lc to remove the things you can’t use, substr to handle parts of a string, and @ARGV to take in input from the command line.
The key for me is to put the plaintext into an array, and instead of going [0][0],[0][1], go [0][0],[1][0]. I considered using substr or a regex to remove the first letter from every string, but making a two-dimensional array seemed better to me.
#!/usr/bin/env perl
use strict;
use warnings;
use feature qw{ say postderef signatures };
no warnings qw{ experimental::postderef experimental::signatures };
use JSON;
my $json = JSON->new;
my $string = 'The quick brown fox jumps over the lazy dog';
my $input = scalar @ARGV ? join ' ', @ARGV : $string;
my $code = encypher($input);
say $code;
sub encypher ( $plaintext ) {
$plaintext = lc $plaintext;
$plaintext =~ s/[^a-z]//gmx;
my @work;
while ( length $plaintext >= 8 ) {
my $eight = substr $plaintext, 0,8;
$plaintext =~ s/\w{8}//mix;
push @work, $eight;
}
push @work, $plaintext;
my @cyphertext;
for my $i ( 0 .. scalar @work - 1 ) {
my $word = $work[$i];
for my $j ( 0 .. length $word ) {
my $letter = substr $word, $j,1;
next unless scalar $letter;
$cyphertext[$j][$i] = $letter;
}
}
return join ' ', map { join '', $_->@* } @cyphertext;
}
Challenge 2
Write a script that dumps its own source code. For example, say, the script name is ch-2.pl then the following command should returns nothing.
$ perl ch-2.pl | diff - ch-2.pl
The term for such programs is a Quine. I’ve thought about them and discussed them, even suggesting a JS program hidden in a QR code that, when when run, creates the QR code that it is hidden in.
In this case, however, I decided that the thing to use is $0, which contains the program name.
#!/usr/bin/env perl
use strict;
use warnings;
use Cwd qw{abs_path};
my $file = abs_path($0);
if ( -f $file && open my $fh, '<', $file ) {
print join '', <$fh>;
}
But reading the Quine page in Wikipedia makes me think that I’m not working hard enough. I’ll submit this and supplement if I gain enlightenment before the end of the week.