#!/usr/bin/perl
use warnings;
use strict;

my @isbn = ();
my %hash = ();
for ( 0 .. 100) {
   $isbn[$_] = &gen_isbn_13; 
}
push @isbn, "9780523456789";
push @isbn, "9780523412345";

while(my $pattern = <DATA>) {
    chomp($pattern);
    print "Testing pattern = $pattern\n";
    $hash{$pattern} = &isbn_exists( $pattern, \@isbn );
    print "Matches found! ISBN = $_ \n" for ( @{$hash{$pattern}} );
}

sub isbn_exists {
    my $pattern = shift;
    my $isbn_arrayref = shift;
    my @answer = grep { /\Q$pattern\E$/ } @{ $isbn_arrayref };
    return \@answer;
}

sub gen_isbn_13 {
    my $num = "978";
    for ( 1 .. 10 ) {
        my $digit = int(rand(10));
        $num .= $digit;
    }
    return $num
}
__DATA__
12345
97833
97810
97805