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#! /usr/bin/env perl
use strict;
use warnings;
use feature 'say';
use feature 'signatures';
no warnings "experimental::signatures";
my $S = shift(@ARGV) // 'THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG';
die "Illegal characters" unless $S =~ /^[A-Z\s]+$/;
my $N = shift(@ARGV) // 3;
die "Illegal shift $N" if $N !~ /^\-?\d+$/ || $N < -25 || $N > 25;
say join("", map { caesar($_, $N) } split(//, $S));
sub caesar ($char, $shift)
{
return $char if $char eq " ";
my $code = ord($char);
$code -= $shift;
$code += 26 if $code < 65; # 'A'
$code -= 26 if $code > 90; # 'Z'
return chr($code);
}
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