<$data> for 1 .. 1;

It reads one line from the file.  I suppose it may have originally been something like

<$data> for 1 .. 3;
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with the intention to skip a few lines at the beginning of the file, before starting to process the rest.  But then later it turned out that only one line was to be skipped, and the author left in the (in this case superfluous) for loop — possibly anticipating it might become useful again in the future...