In your $outhandle assignments, use references to typeglobs as filehandles, as in:

perl -e 'my $foo = \*STDOUT; print $foo "Foo!$/"'
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Why don't you leave the files closed till you know which you need? Then you could pick the correct filename instead and open only that.

my %platfile = (
    NT => 'nt.html',
    UNIX => 'unix.html',
    MAIL => 'mail.html'
);
#...
{
    open my $out, '>>', "$filepath/$platfile{$classHash{$class}}"
      or die $!;
    # ...
}
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At that point, we run into another problem with your code. What is in %classHash? You iterate through all the keys twice - nested. Surely that's not what you should be doing.

After Compline,
Zaxo