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...

In reply to Re: Preventing duplicate info from being pushed into an array by apl
in thread Preventing duplicate info from being pushed into an array by neo1491

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