my @Book = ();
my %MatchFound;

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

##</code><code>##

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