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while(<>) {
    if(/^PORNUM:\s*(\S+)/m) {
...
    }
    print;
}

my %skip = map { $_ => 1 } 
  qw(PP22x43@.5 PC12x120/25);

while(<>) {
    next if /^PORNUM:\s*(\S+)/m and exists $skip{$1};
    print;
}

while(<EXCLUDE>) {
    if(/^PORNUM:\s*(\S+)/) {
        $skip{$1} = 1;
    }
}