cyclic_pattern.pl

#!/usr/bin/env perl

use strict;
use warnings;
use Getopt::Long;

sub gen_pattern {
    my ($size) = @_;
    my @sym1 = "A" .. "Z";
    my @sym2 = "a" .. "Z";
    my @sym3 = "0" .. "9";

    my $pattern = "";
    GEN:
    while (length($pattern) < $size) {
        for my $a (@sym1) {
            for my $b (@sym2) {
                for my $c (@sym3) {
                    $pattern .= $a if length($pattern) < $size;
                    $pattern .= $b if length($pattern) < $size;
                    $pattern .= $c if length($pattern) < $size;
                    last GEN if length($pattern) == $size;
                }
            }
        }
    }
    $pattern;
}


my ($size, $find);

my $input = "-";
my $output = "-";

GetOptions(
    "s|size=i"    => \$size,
    "f|find=s"    => \$find,
    "i|input=s"   => \$input,
    "o|output=s"  => \$output,
);

open(my $out, ">$output");
open(my $in, "<$input");

if (defined($size) && $size > 0) {
    print $out gen_pattern($size), "\n";
}

if (defined($find) && length($find) > 0) {
    my $pattern = join '', map { chomp; $_ } <$in>;
    my $chunk = join '', reverse map { chr hex } $find =~ /.{2}/g;
    my $offset = index($pattern, $chunk);
    die "Offset not found" if $offset < 0;
    print "Offset: $offset\n";
}