Nice, but instead of compiling {number of collections} * {number of required items} regexps, swap your loops to only compile {number of required items} regexps. 

foreach my $item ( @required ) {
  foreach my $collection ( @collections ) {
    $collection .= " $item" unless $collection =~ /\b$item\b/;
  }
}

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In reply to Re^2: are they all there? by ikegami
in thread are they all there? by anadem

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