When dealing with lists and particularly intermediate lists in map/grep chains, it's sometimes difficult (or even impossible?) to know the number of list elements at runtime. This can be handled with yet another map expression:

c:\@Work\Perl\monks>perl -wMstrict -le
"print
   map  sprintf(q{`%s' }, $_),
   grep m{ \A [aeiou] }xms,
   qw(elements comprising this list unknown in advance)
   ;
"
`elements' `unknown' `in' `advance'
[download]

This could be handled with an explicit intermediate array, but it's arguably more awkward:

c:\@Work\Perl\monks>perl -wMstrict -le
"printf do {
   my @elems =
     grep m{ \A [aeiou] }xms,
     qw(elements within this list unknown in advance)
     ;
   qq/@{[ q{`%s' } x @elems ]}/, @elems;
   };
"
`elements' `unknown' `in' `advance'
[download]

(This doesn't reveal any new-found capability of sprintf, but that's life.)