It's just tie()ing.

use Tie::PerFH;
tie $format, 'Tie::PerFH';

@date_info = qw( 12 3 1985 );
$format = '%02d-%02d-%04d';

open FH, ">some.file" or die "some.file error: $!";
select FH;
$format = '%02d/%02d/%04d';
printf $format, @date_info;
close FH;

select STDOUT;

printf $format, @date_info;
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Maybe it's less useful than we'd (I'd?) like, but it's here, and it's not going away. :)

$_="goto+F.print+chop;\n=yhpaj";F1:eval