File management sample codes?

Questions & Help Questions
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5 
defmodule sort_files_by_extension do
  def sort_files do
    File.ls!("./test")
    |> Enum.map(fn filename -> 
         extname = Path.extname(filename)  #=> ".jpg"
         basename = Path.basename(filename, extname)  #=> "IMG_XXXX"
         {basename, extname, filename}
       end)
    |> Enum.map(&make_extension_dir/1)
    |> Enum.map(&dedup/1)
    |> Enum.each(&move_extension_directory/1)

  defp make_extension_dir({_, "." <> extension, _} = arg) do
    File.mkdir_p!("./#{extension}")
    arg  # just return the argument for other `Enum.map`
  end

  defp dedup(arg, suffix \\ 0)

  defp dedup({basename, "." <> extension, filename} = arg, 0) do
    if File.exists?("#{extension}/#{filename}") do
      dedup(arg, 1)
    else
      arg
    end  
  end

  defp dedup({basename, "." <> extension = extname, filename} = arg, suffix) do
    if File.exists?("#{extension}/#{basename}_#{suffix}.#{extension}") do
      dedup(arg, suffix + 1)
    else
      {"#{basename}_#{suffix}", extname, filename}
    end 
  end

  defp move_to_extension_directory({basename, "." <> extension, filename}) do
    File.rename!("./test/#{filename}", "./#{extension}/#{basename}.#{extension}")
  end
end

A few suggestions:

  1. Enum.each is for pure side effects (e.g. pure file system operations). It’s not chainable. Use Enum.map instead.
  2. You can wrap all the information in a tuple, and pattern match on it in the function parameters.
  3. You can trust the file system to do the right thing (e.g. File.mkdir_p!)
  4. Hail recursion!