open (my $file, '<', 'data.bin');
binmode $file;
my $binary_data = <$file>;
$binary_data =~ /(.)(.){$1}/; # how can I do something like that?
#or better yet
$binary_data =~ /(.)(.){(?{unpack 'H*', $1})}/; # ?
# or may be
/(.)(?{unpack 'H*', $1})(.){$^R}/; # ???

##</code><code>##

/(.)((??{'.' x $1}))/;

##</code><code>##

$_ = "3aaaa\nbbbb\nccccc\nddddd";
/(\d)((??{'.*?\n' x $1}))/;
print $2; # aaaa\nbbbb\nccccc\n
# how to assign a value aaaa\n of $3, bbbb\n -> $4 etc ?