To slightly simplify what FunkyMonk said, if you're not concerned about preserving the order the matches were found:

my @Book = ();
my %MatchFound;

foreach (@Book) {
  $MatchFound{$_}++ if ( /\bPerl\b/i && /\bMonks\b/i && /\bRule\b/i );
}
[download]

or even

my @Book       = ();
my %MatchFound = map{ $MatchFound{$_}++ if ( /\bPerl\b/i && /\bMonks\b
+/i && /\bRule\b/i ) } @Book;
[download]

Both, alas, are untested...