...I'm thinking that there might be a little increase in speed here:

($key,$value) = split (/=/, $pair);
chomp ($value);
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Instead of a call to split() and another to chomp(), it might work just to use a regular expression to get the terms.

($key,$value) = ($pair =~ /^([^=]+)=(.*)$/);
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I don't know if it helps in a significant way, but it's something I would have instinctively tried. (Of course, if you spend half a day bulletproofing the regular expression, it probably wouldn't have been worth it.)

---v