Update: The golf dream team of Ton Hospel, Eugene van der Pijll, Mtv Europe and Keith C Ivey whittled 15 strokes from my initial offering:

#!perl -l
$_=$"x2**(pop||4);s'$'/\\',print,s/(?<=\\)../$&^aD^n8/egwhile+s\^ \\
[download]

Here are some other solutions (without default argument) they concocted during their fidgeting:

$_=$"x(1<<pop);print,s/(?<=\\)../$&^"\17|"/egwhile+s^\n?$^/\\\n^,s\^ \
+\
$_=$"x(1<<pop).$/;print,s/(?<=\\)../$&^"\17|"/egwhile+s^$^/\\^,s\^ \\
-lX $_=$"x2**pop;print,s/(?<=\\)../$&^"\17|"/egwhile+s*$*/\\**s+^ ++
-lX $_=$"x2**pop;print,s/(?<=\\)../$&^"\17|"/egwhile+s-^ (.*)-$+/\\-
-l $_=$"x2**pop;s'$'/\\',print,s/(?<=\\)../$&^"\17|"/egwhile+s\^ \\
-l $_=$"x2**pop;s'$'/\\',print,s/(?<=\\)../$&^aD^n8/egwhile+s\^ \\
[download]