I don't see how your code could work at all. Your regex won't match any of the lines you've shown, so $1 and $2 are going to be empty. You've got TWO format items in your printf(), but you're only supplying ONE item to that format list. And you've got a precedence problem with the ?: operator and addition. Try this:

while (<>) {
  if (/^(\w+)\s+(\d+)(.*)/) {
    printf "%s %d %s\n", $1, (exists $disk{$1} ? 0 : ($2+$partition)),
+ $3;
  }
  else { print }
}
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