Nice, but I have one nitpick:

my $thisout = substr($i, 0, index($i, ".")) . ".txt"
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What about names like "my.file.rpt" (pretty common style on *nix)?

Since we are already through with $i (let's call it $file from now on), we can do:

$file =~ s/\.rpt$/.txt/i; #case insensitive
open OUTPUT, ">$file";
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