A couple of other changes you might consider are using a hash to check if a line is one that should be kept, and outputting lines you want to keep immediately, rather than accumulating them all in memory:

my %validbufs = map { $_ => 1 } @validbufs;
while ($line = <BUFFER>) {
       $searchfield=(split /\'/,$line)[1];
       print $line if $validbufs{$searchfield}
}
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