I came up with the term anonymous filehandles on-the-fly as I didn't know what else it is called.

Is there a formal name for this feature?

Thanks.

Perl Cookbook just refers to it as "<>" and doesn't mention any name for it.

Regarding your other response, yes, perl is smart enough to automagically close any open files when the program exits, regardless of how/when they were opened. It may close files opened by <> sooner (e.g., when each of them hits EOF), but I haven't found anything which clearly states that one way or the other.

If you read perlop's description of <> (the "null filehandle" in its nomenclature) it expands out the construct to:

           unshift(@ARGV, '-') unless @ARGV;
           while ($ARGV = shift) {
               open(ARGV, $ARGV);
               while (<ARGV>) {
                   ...         # code for each line
               }
           }
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When you re-open any existing filehandle the underlying file is implicitly closed; so each time through the loop the prior file will be closed before the handle is reused.