A couple of days ago I released a new version of Sort::Key supporting multikey sorting:

use Sort::Key::Maker sort_pic_names =>
   # define how to extract the keys
   sub { /^F(\d*)(\w*)/; $1, ($2||"\xff") },
   # and their types
   qw(number string);

my @arr = ... ;
# and just use the new sorter
my @sorted_arr = sort_pic_names @arr;
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update: I have notice that there is some bug in the module that causes the multikey functionality to corrupt memory in some systems... so don't use it yet!