#!/usr/bin/perl -l
$c .= 1 + int rand 6 for 1 .. 4;      # Build up the secret

while (<>) {
    /^\d{4}$|!/ || next;              # Check user entered 4 digits

    $_ .= $c;

    1 while s!(.)(.{4})\1!?$2*!s;       # Match in right position

    1 while s!(\d)(.*\n.*)\1!+$2!;      # Match somewhere

    print /[*+]/g;                      # Print matches

    /\*{4}|!/ && exit;
}