#!/usr/bin/perl

use warnings;
use strict;
use Getopt::Std;

my %opt;

usage() unless (getopts('rRcCaA', \%opt));
usage() unless @ARGV;

if($opt{'r'} || $opt{'R'}) {
    while(<>) {
        tr/a-zA-Z/n-za-mN-ZA-M/;
        print;
    }
} elsif($opt{'c'}) {
    while(<>) {
        tr/a-zA-Z/d-za-cD-ZA-C/;
        print;
    }
} elsif($opt{'C'}) {
    while(<>) {
        tr/d-za-cD-ZA-C/a-zA-Z/;
        print;
    }
} elsif($opt{'a'}) {
    while(my $line = <>) {
        @_ = split//, $line;
        map { print ord($_), " "; } @_;
        print "\n";
    }
} elsif($opt{'A'}) {
    while(my $line = <>) {
        @_ = split/ /, $line;
        map { print chr($_); } @_;
        print "\n";
    }
}

sub usage {
    print << "__END__";
    -c = encrypt with Caesar encryption
    -C = decrypt from Caesar encryption
    -r = encrypt with rot13
    -R = decrypt from rot13
    -a = encrypt to numerical equivalent
    -A = decrypt back to ASCII
    example using files:
    perl $0 -r plain.txt
    perl $0 -C encrypted.txt
    example using STDIN:
    perl $0 -r <ENTER, type text>
__END__
    exit 1;
}
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