What I think you are trying to do is these steps:

• extract the key from the paragraph with a regex
• look up this key in your hash and respond to it

So, what this means in code:

while(<>) {
    if(/^PORNUM:\s*(\S+)/m) {
        if(exists $skip{$1}) {
            # It matches, and ought to be skipped
            next;
        }
    }
    print;
}
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That doesn't look too bad, does it? (And it can be reduced a lot more, at the cost of readability for beginners. But IMHO, it's worth it.)

All you still have to do, is initialize the %skip hash first, for example, like this:

my %skip = map { $_ => 1 } 
  qw(PP22x43@.5 PC12x120/25);
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Alternatively, you can read data from a string or from the DATA section (or even from an external file), and split on whitespace.

p.s. The reduced code that I talked about, can be something like this:

while(<>) {
    next if /^PORNUM:\s*(\S+)/m and exists $skip{$1};
    print;
}
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Update: Oh, now I see: you put in the format for an "exclude" file. well, you'll have to read that first.

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