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#!/usr/bin/perl -s
use v5.16;
use Test2::V0;
use experimental 'signatures';
our ($tests, $examples, $verbose, $offset);
run_tests() if $tests || $examples; # does not return
say(<<EOS), exit unless @ARGV;
usage: $0 [-examples] [-tests] [-verbose] [-offset=n] [text...]
-examples
run the examples from the challenge
-tests
run some tests
-verbose
show cipher
-offset=n
Use n as cipher offset. Default: 13
text...
words to be encoded
EOS
### Input and Output
say caesar($offset // 13)->(@ARGV);
### Implementation
# Generate a Caesar Cipher encoder with offset n. Use -n for a
# matching decoder.
sub caesar ($n) {
state $plain = join '', 'A' .. 'Z';
$n %= length $plain;
my $cipher = $n ?
# last $n chars + first chars except last $n chars.
substr($plain, -$n, $n) . substr($plain, 0, -$n) :
$plain;
say "Offset: $n\nPlain: $plain\nCipher: $cipher" if $verbose;
# Encode string(s) using Caesar Cipher. All characters outside plain
# capital latin letters and SPACE are silently discarded. The SPACE
# character will be passed unencoded. Does not rely on a contiguous
# character encoding of letters. (EBCDIC!)
sub (@s) {
local $_ = "@s";
# tr/// does not interpolate.
eval "tr/ $plain//cd";
eval "tr/ $plain/ $cipher/r";
}
}
### Examples and tests
sub run_tests {
SKIP: {
skip "examples" unless $examples;
is caesar(3)->('THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG'),
'QEB NRFZH YOLTK CLU GRJMP LSBO QEB IXWV ALD', 'example';
}
SKIP: {
skip "tests" unless $tests;
# Create a set of encoders.
my $clear= caesar(0);
my $enc6 = caesar(6);
my $dec6 = caesar(-6);
is $clear->('ABCD'), 'ABCD', 'cleartext';
is $enc6->('EFGH'), 'YZAB', 'wrap positive';
is $dec6->('STUV'), 'YZAB', 'wrap negative';
is $clear->('ABc dEF'), 'AB EF', 'discard illegal characters';
is $clear->(qw(A B C D)), 'A B C D', 'multiple args';
is $dec6->($enc6->('AB CD')), 'AB CD', 'encode/decode';
}
done_testing;
exit;
}
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