hmm.. just some brainstorming (maybe it will lead to something better):

printf( "A float: %12s$/", $root_beer ? sprintf(".4f",$root_beer) : $r
+oot_beer );

$root_beer = sprintf(".4f",$root_beer) if $root_beer;
printf( "A float: %12s$/", $root_beer );

sub fmt { $_[0] ? sprintf(".4f",$_[0]) : $_[0] }
printf( "A float: %12s$/", fmt($root_beer) );
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