oog! Looking at that split I have no idea what you're trying to extract. Well, not at first glance. All you want is to extract the digit-and-underscore component before the file extensions. How about the simpler:

my @sorted_list =
    map  {$_->[0]}
    sort { $b->[1] cmp $a->[1] }
    map  { /([\d_]+)\.csv\.xml$/ ? [$_,$1] : [$_, 0] }
         @file_list;
[download]

Also, you should avoid using

next if ( $file =~ /^\./ );

One of these days it will come back to haunt you. It is wiser to use the more prosaic form:

next if $file eq '.' or $file eq '..'

Even if it doesn't look as cool because it lacks regexps.