`Variable use immediately follows assignment`

      @files = grep { /^$key\./i } @all_files;
      foreach (@files) {
        unlink("$dir/$_") || &err("can't delete $_ : $!");
      }

      foreach (grep { /^$key\./i } @all_files) {
        unlink("$dir/$_") || &err("can't delete $_ : $!");
      }

There are two good reasons for retaining @files
One is the documentative value of the name
- Not much in this case
The other is to prevent the foreach line from getting too ugly
- I don't think this one is any worse than the line we got rid of